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Title:
REDIRECTION MECHANISM TO SUPPORT NETWORK SHARING/SLICING WITH CU-DU SPLIT FOR RE-ESTABLISHMENT
Document Type and Number:
WIPO Patent Application WO/2020/100053
Kind Code:
A1
Abstract:
Systems and methods for connection reestablishment in a cellular communications system that utilizes Centralized Unit (CU) / Distributed Unit (DU) split are disclosed. In one embodiment, a method performed by a shared distributed unit for connection reestablishment for a User Equipment (UE) is disclosed. The shared distributed unit comprises distributed units of first and second target base stations associated with first and second Public Land Mobile Networks (PLMNs) or first and second network slices, respectively, wherein the first and second target base stations share resources. The method comprises receiving a connection reestablishment request comprising an identity of the UE in a source cell and an identity of the source cell and sending an message to a central unit of the first target base station comprising the identities of the UE and the source cell, and information regarding a cell served by the second target base station using the shared resources.

Inventors:
VESELY ALEXANDER (AT)
FIORANI MATTEO (SE)
MILDH GUNNAR (SE)
CENTONZA ANGELO (SE)
MULLER JULIEN (SE)
MASINI GINO LUCA (SE)
Application Number:
PCT/IB2019/059739
Publication Date:
May 22, 2020
Filing Date:
November 13, 2019
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
ERICSSON TELEFON AB L M (SE)
International Classes:
H04W76/19; H04W48/18
Other References:
ERICSSON ET AL: "RAN sharing with multiple Cell ID broadcast", vol. RAN WG3, no. Spokane, WA, U.S.; 20181112 - 20181116, 11 November 2018 (2018-11-11), XP051558612, Retrieved from the Internet [retrieved on 20181111]
ERICSSON: "Response paper to R3-185596 and R3-185739", vol. RAN WG3, no. Chengdu, P.R. China; 20181008 - 20181012, 4 October 2018 (2018-10-04), XP051529315, Retrieved from the Internet [retrieved on 20181004]
ERICSSON: "Response paper to R3-185845", vol. RAN WG3, no. Chengdu, P.R. China; 20181008 - 20181012, 4 October 2018 (2018-10-04), XP051529318, Retrieved from the Internet [retrieved on 20181004]
Attorney, Agent or Firm:
BEVINS, R. Chad (US)
Download PDF:
Claims:
Claims

What is claimed is:

1. A method performed for connection reestablishment of a User Equipment, UE, (600) in a cellular communications system, comprising:

• at a shared distributed unit (608) that comprises: (a) a distributed unit (610A) of a first target base station (600) associated with a first Public Land Mobile

Network, PLMN, or a first network slice and (b) a distributed unit (610B) of a second target base station (602) associated with a second PLMN or a second network slice, wherein the first target base station (600) and the second target base station (602) share resources:

o receiving (Fig. 5, step 1), from the UE (620) at the distributed unit (610A) of the first target base station (600), a connection reestablishment request comprising an identity of the UE (620) in a source cell to which the UE (620) was connected prior to sending the connection reestablishment request and an identity of the source cell; and

o sending (Fig. 5, step 2) an initial message to a central unit (612A) of the first target base station (600), the initial message comprising: (a) the identity of the UE (620) in the source cell, (b) the identity of the source cell, and (c) information regarding a second cell served by the second target base station (602) using the shared resources, wherein the shared resources comprise physical layer resources, Medium Access Control, MAC, layer resources, or both physical layer resources and MAC layer resources;

• at the central unit (612A) of the first target base station (600):

o receiving (Fig. 5, step 2) the initial message from the shared distributed unit (608) of the first target base station (602) and the second target base station (602); and

o sending (Fig. 5, step 3), to a central unit (618A) of a first source base

station associated with the first PLMN or the first network slice, a request to retrieve a UE context of the UE (620), the request comprising the identity of the UE (620) in the source cell, the identity of the source cell, and the information regarding the second cell served by the second target base station using the shared resources; • at the central unit (618A) of the first source base station (604), wherein the first source base station (604) shares resources with a second source base station (606) associated with a second PLMN or a second network slice and the resources shared by the first and second target base stations (600 and 602) comprise physical layer resources, MAC layer resources, or both physical layer resources and MAC layer resources:

o receiving (Fig. 5, step 3) the request to retrieve the UE context of the UE (620) from the central unit (612A) of the first target base station (600); o determining (Fig. 5, step 4) that the UE context of the UE (620) cannot be found by the central unit (618A) of the first source base station (604); and o upon determining that the UE context of the UE (620) cannot be found, sending (Fig. 5, step 5) a message to a shared distributed unit (614) of the first source base station (604) and the second source base station (606) that allocated the identity of the UE (620) in the source cell to initiate redirection of the request to retrieve the UE context of the UE (620) to a correct central unit (618B) of the second source base station (606);

• at the second shared distributed unit (614):

o receiving (Fig. 5, step 5), from the central unit (618A) of the first source base station (604), the message to initiate redirection of the request to retrieve the UE context of the UE (620) to a correct central unit; o identifying (Fig. 5, step 6) a correct central unit (618B) of the second

source base station (606) from which to retrieve the UE context of the UE (620) based on the message to initiate redirection of the request to retrieve the UE context of the UE (620); and

o sending (Fig. 5, step 7), to the correct central unit (618B) of the second source base station (606), a message that redirects the request to retrieve the UE context of the UE (620) to the correct central unit (618B) of the second source base station (606);

• at the correct central unit (618B) of the second source base station (606):

o receiving (Fig. 5, step 7), from the shared distributed unit (614) of the first source base station (604) and the second source base station (606), the message that redirects the request to retrieve the UE context of the UE (620) to the central unit (618B) of the second source base station (606); o upon receiving the message, retrieving the UE context of the UE (620); and

o sending (Fig. 5, step 8) the UE context of the UE (620) to a central unit (612B) of the second target base station (602), wherein the central unit (612B) of the second target base station (602) is associated with the shared distributed unit (608) of the first target base station (600) and the second target base station (602) at which the connection reestablishment request was received from the UE (620);

• at the central unit (612B) of the second target base station (606):

o receiving (Fig. 5, step 8) the UE context of the UE (620) from the correct central unit (618B) of the second source base station (606); and o sending (Fig. 5, step 10), to the shared distributed unit (608) of the first target base station (600) and the second target base station (602), a message that triggers transfer of the connection reestablishment request procedure from the distributed unit (610A) of the first target base station (600) to the distributed unit (610B) of the second target base station (600).

2. A method performed by a shared distributed unit (608) that comprises: (a) a distributed unit (610A) of a first target base station (600) associated with a first Public Land Mobile Network, PLMN, or a first network slice and (b) a distributed unit (610B) of a second target base station (602) associated with a second PLMN or a second network slice, for connection reestablishment for a User Equipment, UE, (600), wherein the first target base station (600) and the second target base station (602) share resources, the method comprising:

receiving (Fig. 5, step 1), from the UE (620) at the distributed unit (610A) of the first target base station (600), a connection reestablishment request comprising an identity of the UE (620) in a source cell to which the UE (620) was connected prior to sending the connection reestablishment request and an identity of the source cell; and sending (Fig. 5, step 2) an initial message to a central unit (612A) of the first target base station (600), the initial message comprising: (a) the identity of the UE (620) in the source cell, (b) the identity of the source cell, and (c) information regarding a second cell served by the second target base station (602) using the shared resources, wherein the shared resources comprise physical layer resources, Medium Access Control, MAC, layer resources, or both physical layer resources and MAC layer resources.

3. The method of claim 2 wherein the connection reestablishment request is a Radio Resource Control, RRC, Reestablishment Request.

4. The method of claim 2 or 3 wherein the information regarding the second cell served by the second target base station (602) using the shared physical layer and/or MAC layer resources comprises a Cell Group Identifier, CGI, of the second cell, a PLMN identity, ID, of the second PLMN associated with the second cell, or both a CGI of the second cell and the PLMN ID of the second PLMN associated with the second cell.

5. The method of any of claims 2 to 4 wherein the initial message comprises at least a portion of the connection reestablishment request.

6. The method of any of claims 2 to 5 further comprising:

receiving (Fig. 5, step 10), from a central unit (612B) of the second target base station (602), a message that transfers the connection reestablishment procedure for the UE (620) from the distributed unit (610A) of the first target base station (600) to the distributed unit (610B) of the second target base station (602); and

completing (Fig. 5, steps 11-13) the connection reestablishment procedure.

7. A shared distributed unit (608) that comprises: (a) a distributed unit (610A) of a first target base station (600) associated with a first Public Land Mobile Network, PLMN, or a first network slice and (b) a distributed unit (610B) of a second target base station (602) associated with a second PLMN or a second network slice, for connection reestablishment for a User Equipment (600), wherein the first target base station (600) and the second target base station (602) share resources, the shared distributed unit (608) adapted to: receive (Fig. 5, step 1), from the UE (620) at the distributed unit (610A) of the first target base station (600), a connection reestablishment request comprising an identity of the UE (620) in a source cell to which the UE (620) was connected prior to sending the connection reestablishment request and an identity of the source cell; and send (Fig. 5, step 2) an initial message to a central unit (612A) of the first target base station (600), the initial message comprising: (a) the identity of the UE (620) in the source cell, (b) the identity of the source cell, and (c) information regarding a second cell served by the second target base station (602) using the shared resources, wherein the shared resources comprise physical layer resources, Medium Access

Control, MAC, layer resources, or both physical layer resources and MAC layer resources.

8. A node implementing a shared distributed unit (608) that comprises: (a) a distributed unit (610A) of a first target base station (600) associated with a first Public Land Mobile Network, PLMN, or a first network slice and (b) a distributed unit (610B) of a second target base station (602) associated with a second PLMN or a second network slice, for connection reestablishment for a User Equipment (600), wherein the first target base station (600) and the second target base station (602) share resources, the node comprising:

a network interface; and

processing circuitry associated with the network interface, the processing circuitry configured to cause the node to:

receive (Fig. 5, step 1), from the UE (620) at the distributed unit (610A) of the first target base station (600), a connection reestablishment request comprising an identity of the UE (620) in a source cell to which the UE (620) was connected prior to sending the connection reestablishment request and an identity of the source cell; and

send (Fig. 5, step 2) an initial message to a central unit (612A) of the first target base station (600), the initial message comprising: (a) the identity of the UE (620) in the source cell, (b) the identity of the source cell, and (c) information regarding a second cell served by the second target base station (602) using the shared resources, wherein the shared resources comprise physical layer resources, Medium Access Control, MAC, layer resources, or both physical layer resources and MAC layer resources.

9. A method performed by a central unit (612A) of a first target base station (600) associated with a first Public Land Mobile Network, PLMN, or a first network slice for a connection reestablishment procedure for a User Equipment, UE, (600), wherein the first target base station (600) shares resources with a second target base station (602) associated with a second PLMN or a second network slice, the method comprising:

receiving (Fig. 5, step 2) an initial message from a shared distributed unit (608) of the first target base station (602) and the second target base station (602), the initial message comprising: (a) an identity of the UE (620) in a source cell to which the UE (620) was connected prior to sending a connection reestablishment request that triggered the initial message, (b) the identity of the source cell, and (c) information regarding a second cell served by the second target base station using the shared resources, wherein the shared resources comprise physical layer resources, Medium Access Control, MAC, layer resources, or both physical layer resources and MAC layer resources; and

sending (Fig. 5, step 3), to a central unit (618A) of a first source base station associated with the first PLMN or the first network slice, a request to retrieve a UE context of the UE (620), the request comprising the identity of the UE (620) in the source cell, the identity of the source cell, and the information regarding the second cell served by the second target base station using the shared resources.

10. The method of claim 9 wherein the connection reestablishment request is a Radio Resource Control, RRC, Reestablishment Request.

11. The method of claim 9 or 10 wherein the information regarding the second cell served by the second target base station (602) using the shared resources comprises a Cell Group Identifier, CGI, of the second cell, a PLMN identity, ID, of the second PLMN associated with the second cell, or both a CGI of the second cell and the PLMN ID of the second PLMN associated with the second cell.

12. The method of any of claims 9 to 11 wherein both the initial message and the request comprise at least a portion of the connection reestablishment request.

13. A central unit (612A) of a first target base station (600) associated with a first Public Land Mobile Network, PLMN, or a first network slice for a connection

reestablishment procedure for a User Equipment, UE, (600), wherein the first target base station (600) shares resources with a second target base station (602) associated with a second PLMN or a second network slice, the central unit (612A) adapted to:

receive (Fig. 5, step 2) an initial message from a shared distributed unit (608) of the first target base station (602) and the second target base station (602), the initial message comprising: (a) an identity of the UE (620) in a source cell to which the UE (620) was connected prior to sending a connection reestablishment request that triggered the initial message, (b) the identity of the source cell, and (c) information regarding a second cell served by the second target base station using the shared resources, wherein the shared resources comprise physical layer resources, Medium Access Control, MAC, layer resources, or both physical layer resources and MAC layer resources; and

send (Fig. 5, step 3), to a central unit (618A) of a first source base station associated with the first PLMN or the first network slice, a request to retrieve a UE context of the UE (620), the request comprising the identity of the UE (620) in the source cell, the identity of the source cell, and the information regarding the second cell served by the second target base station using the shared resources.

14. A node implementing a central unit (612A) of a first target base station (600) associated with a first Public Land Mobile Network, PLMN, or a first network slice for a connection reestablishment procedure for a User Equipment, UE, (600), wherein the first target base station (600) shares resources with a second target base station (602) associated with a second PLMN or a second network slice, the node comprising:

a network interface; and

processing circuitry associated with the network interface, the processing circuitry configured to cause the node to:

receive (Fig. 5, step 2) an initial message from a shared distributed unit

(608) of the first target base station (602) and the second target base station (602), the initial message comprising: (a) an identity of the UE (620) in a source cell to which the UE (620) was connected prior to sending a connection reestablishment request that triggered the initial message, (b) the identity of the source cell, and (c) information regarding a second cell served by the second target base station using the shared resources, wherein the shared resources comprise physical layer resources, Medium Access Control, MAC, layer resources, or both physical layer resources and MAC layer resources; and

send (Fig. 5, step 3), to a central unit (618A) of a first source base station associated with the first PLMN or the first network slice, a request to retrieve a UE context of the UE (620), the request comprising the identity of the UE (620) in the source cell, the identity of the source cell, and the information regarding the second cell served by the second target base station using the shared resources.

15. A method performed by a central unit (618A) of a first source base station (604) associated with a first Public Land Mobile Network, PLMN, or a first network slice for a connection reestablishment procedure for a User Equipment, UE, (600), wherein the first source base station (604) shares resources with a second source base station (606) associated with a second PLMN or a second network slice, the method comprising:

receiving (Fig. 5, step 3), from a central unit (612A) of a first target base station (600) associated with the first PLMN or the first network slice, a request to retrieve a UE context of the UE (620), the request comprising: (a) an identity of the UE (620) in a source cell to which the UE (620) was connected prior to connection reestablishment,

(b) the identity of the source cell, and (c) information regarding a second cell served by a second target base station (602) that shares resources with the first target base station (600), wherein the resources shared by the first and second source base stations (604 and 606) and the resources shared by the first and second target base stations (600 and 602) comprise physical layer resources, Medium Access Control, MAC, layer resources, or both physical layer resources and MAC layer resources;

determining (Fig. 5, step 4) that the UE context of the UE (620) cannot be found by the central unit (618A) of the first source base station (604); and

upon determining that the UE context of the UE (620) cannot be found, sending (Fig. 5, step 5) a message to a shared distributed unit (614) of the first source base station (604) and the second source base station (606) that allocated the identity of the UE (620) in the source cell to initiate redirection of the request to retrieve the UE context of the UE (620) to a correct central unit (618B) of the second source base station (606).

16. The method of claim 15 wherein the request to retrieve the UE context of the UE (620) further comprises at least a portion of a connection reestablishment request message sent by the UE (620) to initiate the connection reestablishment procedure.

17. The method of claim 15 or 16 wherein the message sent to the shared

distributed unit (614) of the first source base station (604) and the second source base station (606) that allocated the identity of the UE (620) in the source cell comprises: a. the identity of the UE (620) in the source cell;

b. at least a portion of a connection reestablishment request message sent by the UE (620) to initiate the connection reestablishment procedure; c. at least a portion of the request to retrieve the UE context of the UE (620); d. the information regarding the second cell served by the second target base station (602) using the shared resources; or

e. any combination of two or more of a-d.

18. The method of any of claims 15 to 17 wherein the information regarding the second cell served by the second target base station (602) using the shared resources comprises a Cell Group Identifier, CGI, of the second cell, a PLMN identity, ID, of the second PLMN associated with the second cell, or both the CGI of the second cell and the PLMN ID of the second PLMN associated with the second cell.

19. A central unit (618A) of a first source base station (604) associated with a first Public Land Mobile Network, PLMN, or a first network slice for a connection

reestablishment procedure for a User Equipment, UE, (600), wherein the first source base station (604) shares resources with a second source base station (606) associated with a second PLMN or a second network slice, the central unit (618A) adapted to: receive (Fig. 5, step 3), from a central unit (612A) of a first target base station (600) associated with the first PLMN or the first network slice, a request to retrieve a UE context of the UE (620), the request comprising: (a) an identity of the UE (620) in a source cell to which the UE (620) was connected prior to connection reestablishment,

(b) the identity of the source cell, and (c) information regarding a second cell served by a second target base station (602) that shares resources with the first target base station (600), wherein the resources shared by the first and second source base stations (604 and 606) and the resources shared by the first and second target base stations (600 and 602) comprise physical layer resources, Medium Access Control, MAC, layer resources, or both physical layer resources and MAC layer resources;

determine (Fig. 5, step 4) that the UE context of the UE (620) cannot be found by the central unit (618A) of the first source base station (604); and

upon determining that the UE context of the UE (620) cannot be found, send (Fig. 5, step 5) a message to a shared distributed unit (614) of the first source base station (604) and the second source base station (606) that allocated the identity of the UE (620) in the source cell to initiate redirection of the request to retrieve the UE context of the UE (620) to a correct central unit (618B) of the second source base station (606).

20. A node implementing a central unit (618A) of a first source base station (604) associated with a first Public Land Mobile Network, PLMN, or a first network slice for a connection reestablishment procedure for a User Equipment, UE, (600), wherein the first source base station (604) shares resources with a second source base station (606) associated with a second PLMN or a second network slice, the node comprising:

a network interface; and

processing circuitry associated with the network interface, the processing circuitry configured to cause the node to:

receive (Fig. 5, step 3), from a central unit (612A) of a first target base station (600) associated with the first PLMN or the first network slice, a request to retrieve a UE context of the UE (620), the request comprising: (a) an identity of the UE (620) in a source cell to which the UE (620) was connected prior to connection reestablishment, (b) the identity of the source cell, and (c)

information regarding a second cell served by a second target base station (602) that shares resources with the first target base station (600), wherein the resources shared by the first and second source base stations (604 and 606) and the resources shared by the first and second target base stations (600 and 602) comprise physical layer resources, Medium Access Control, MAC, layer resources, or both physical layer resources and MAC layer resources;

determine (Fig. 5, step 4) that the UE context of the UE (620) cannot be found by the central unit (618A) of the first source base station (604); and

upon determining that the UE context of the UE (620) cannot be found, send (Fig. 5, step 5) a message to a shared distributed unit (614) of the first source base station (604) and the second source base station (606) that allocated the identity of the UE (620) in the source cell to initiate redirection of the request to retrieve the UE context of the UE (620) to a correct central unit (618B) of the second source base station (606).

21. A method performed by a second shared distributed unit (614) of: (a) a first source base station (604) associated with a first PLMN or a first network slice and (b) a second source base station (606) associated with a second PLMN or a second network slice, for a connection reestablishment procedure for a User Equipment, UE, (600), wherein the first source base station (604) and the second source base station (606) share resources, the method comprising:

receiving (Fig. 5, step 5), from a central unit (618A) of the first source base station (604), a message to initiate redirection of a request to retrieve a UE context of the UE (620) to a correct central unit, the message comprising: (a) an identity of the UE (620) in a source cell to which the UE (620) was connected prior to connection reestablishment, (b) the identity of the source cell, and (c) information regarding a second cell served by a second target base station (602) associated with the second PLMN or the second network slice that shares resources with a first target base station (600) associated with the first PLMN or the first network slice, wherein the resources shared by the first and second source base stations (604 and 606) and the resources shared by the first and second target base stations (600 and 602) comprise physical layer resources, Medium Access Control, MAC, layer resources, or both physical layer resources and MAC layer resources;

identifying (Fig. 5, step 6) a correct central unit (618B) of the second source base station (606) from which to retrieve the UE context of the UE (620) based on the message to initiate redirection of the request to retrieve the UE context of the UE (620); and

sending (Fig. 5, step 7), to the correct central unit (618B) of the second source base station (606), a message that redirects the request to retrieve the UE context of the UE (620) to the correct central unit (618B) of the second source base station (606).

22. The method of claim 21 wherein the message to initiate redirection of the request to receive a UE context of the UE (620) comprises the identity of the UE (620) in the source cell and the information regarding the second cell served by the second target base station (602).

23. The method of claim 21 or 22 wherein the message to initiate redirection of the request to receive a UE context of the UE (620) comprises at least a portion of a connection reestablishment request transmitted by the UE (620) to initiate connection reestablishment.

24. The method of any of claims 21 to 23 wherein the message that redirects the request to retrieve the UE context of the UE (620) comprises the identity of the UE (620) in the source cell and the information regarding the second cell served by the second target base station (602) using the shared resources.

25. The method of any of claims 21 to 24 wherein the message that redirects the request to retrieve the UE context of the UE (620) comprises at least a portion of a connection reestablishment request transmitted by the UE (620) to initiate connection reestablishment.

26. The method of any of claims 21 to 25 wherein the information regarding the second cell served by the second target base station (602) using the shared resources comprises a Cell Group Identifier, CGI, of the second cell, a PLMN identity, ID, of the second PLMN associated with the second cell, or both the CGI of the second cell and the PLMN ID of the second PLMN associated with the second cell.

27. A second shared distributed unit (614) of: (a) a first source base station (604) associated with a first PLMN or a first network slice and (b) a second source base station (606) associated with a second PLMN or a second network slice, for a connection reestablishment procedure for a User Equipment, UE, (600), wherein the first source base station (604) and the second source base station (606) share resources, the second shared distributed unit (614) adapted to:

receive (Fig. 5, step 5), from a central unit (618A) of the first source base station (604), a message to initiate redirection of a request to retrieve a UE context of the UE (620) to a correct central unit, the message comprising: (a) an identity of the UE (620) in a source cell to which the UE (620) was connected prior to connection

reestablishment, (b) the identity of the source cell, and (c) information regarding a second cell served by a second target base station (602) associated with the second PLMN or the second network slice that shares resources with a first target base station (600) associated with the first PLMN or the first network slice, wherein the resources shared by the first and second source base stations (604 and 606) and the resources shared by the first and second target base stations (600 and 602) comprise physical layer resources, Medium Access Control, MAC, layer resources, or both physical layer resources and MAC layer resources;

identify (Fig. 5, step 6) a correct central unit (618B) of the second source base station (606) from which to retrieve the UE context of the UE (620) based on the message to initiate redirection of the request to retrieve the UE context of the UE (620); and

send (Fig. 5, step 7), to the correct central unit (618B) of the second source base station (606), a message that redirects the request to retrieve the UE context of the UE (620) to the correct central unit (618B) of the second source base station (606).

28. A node implementing a second shared distributed unit (614) of: (a) a first source base station (604) associated with a first PLMN or a first network slice and (b) a second source base station (606) associated with a second PLMN or a second network slice, for a connection reestablishment procedure for a User Equipment, UE, (600), wherein the first source base station (604) and the second source base station (606) share resources, the node comprising:

a network interface; and processing circuitry associated with the network interface, the processing circuitry configured to cause the node to:

receive (Fig. 5, step 5), from a central unit (618A) of the first source base station (604), a message to initiate redirection of a request to retrieve a UE context of the UE (620) to a correct central unit, the message comprising: (a) an identity of the UE (620) in a source cell to which the UE (620) was connected prior to connection reestablishment, (b) the identity of the source cell, and (c) information regarding a second cell served by a second target base station (602) associated with the second PLMN or the second network slice that shares resources with a first target base station (600) associated with the first PLMN or the first network slice, wherein the resources shared by the first and second source base stations (604 and 606) and the resources shared by the first and second target base stations (600 and 602) comprise physical layer resources, Medium Access Control, MAC, layer resources, or both physical layer resources and MAC layer resources;

identify (Fig. 5, step 6) a correct central unit (618B) of the second source base station (606) from which to retrieve the UE context of the UE (620) based on the message to initiate redirection of the request to retrieve the UE context of the UE (620); and

send (Fig. 5, step 7), to the correct central unit (618B) of the second source base station (606), a message that redirects the request to retrieve the UE context of the UE (620) to the correct central unit (618B) of the second source base station (606).

29. A method performed by a central unit (618B) of a second source base station (606) associated with a second PLMN or a second network slice for a connection reestablishment procedure for a UE (620), wherein the second source base station (606) shares resources with a first source base station (604) associated with a first PLMN or a first network slice, the method comprising:

receiving (Fig. 5, step 7), from a shared distributed unit (614) of the first source base station (604) and the second source base station (606), a message that redirects a request to retrieve a UE context of the UE (620) to the central unit (618 B) of the second source base station (606); upon receiving the message, retrieving the UE context of the UE (620); and sending (Fig. 5, step 8) the UE context of the UE (620) to a central unit (612B) of a second target base station (602) associated with the second PLMN or the second network slice that shares resources with a first target base station (600) associated with the first PLMN or the first network slice, wherein the central unit (612B) of the second target base station (602) is associated with a shared distributed unit (608) of the first target base station (600) and the second target base station (602) at which a respective connection reestablishment request was received from the UE (620).

30. The method of claim 29 wherein the message that redirects the request to retrieve the UE context of the UE (620) comprises the identity of the UE (620) in the source cell and the information regarding the second cell served by the second target base station (602) using the shared resources.

31. The method of claim 29 or 30 wherein the message that redirects the request to retrieve the UE context of the UE (620) comprises at least a portion of the connection reestablishment request from the UE (620).

32. The method of any of claims 29 to 31 wherein the information regarding the second cell served by the second target base station (602) using the shared resources comprises a Cell Group Identifier, CGI, of the second cell, a PLMN identity, ID, of the second PLMN associated with the second cell, or both the CGI of the second cell and the PLMN ID of the second PLMN associated with the second cell.

33. A central unit (618B) of a second source base station (606) associated with a second PLMN or a second network slice for a connection reestablishment procedure for a UE (620), wherein the second source base station (606) shares resources with a first source base station (604) associated with a first PLMN or a first network slice, the central unit (618B) adapted to:

receive (Fig. 5, step 7), from a shared distributed unit (614) of the first source base station (604) and the second source base station (606), a message that redirects a request to retrieve a UE context of the UE (620) to the central unit (618 B) of the second source base station (606); upon receiving the message, retrieve the UE context of the UE (620); and send (Fig. 5, step 8) the UE context of the UE (620) to a central unit (612B) of a second target base station (602) associated with the second PLMN or the second network slice that shares resources with a first target base station (600) associated with the first PLMN or the first network slice, wherein the central unit (612B) of the second target base station (602) is associated with a shared distributed unit (608) of the first target base station (600) and the second target base station (602) at which a respective connection reestablishment request was received from the UE (620).

34. A node implementing a central unit (618B) of a second source base station (606) associated with a second PLMN or a second network slice for a connection

reestablishment procedure for a UE (620), wherein the second source base station (606) shares resources with a first source base station (604) associated with a first PLMN or a first network slice, the node comprising:

a network interface; and

processing circuitry associated with the network interface, the processing circuitry configured to cause the node to:

receive (Fig. 5, step 7), from a shared distributed unit (614) of the first source base station (604) and the second source base station (606), a message that redirects a request to retrieve a UE context of the UE (620) to the central unit (618B) of the second source base station (606);

upon receiving the message, retrieve the UE context of the UE (620); and send (Fig. 5, step 8) the UE context of the UE (620) to a central unit (612B) of a second target base station (602) associated with the second PLMN or the second network slice that shares resources with a first target base station (600) associated with the first PLMN or the first network slice, wherein the central unit (612B) of the second target base station (602) is associated with a shared distributed unit (608) of the first target base station (600) and the second target base station (602) at which a respective connection reestablishment request was received from the UE (620).

35. A method performed by a central unit (612B) of a second target base station (606) associated with a second Public Land Mobile Network, PLMN, or a second network slice, for connection reestablishment for a User Equipment, UE, (600), wherein the second target base station (602) shares resources with a first target base station (600) associated with a first PLMN or a first network slice, the method comprising:

receiving (Fig. 5, step 8) a UE context of the UE (620) from a central unit (618B) of a second source base station (606) associated with the second PLMN or the second network slice, wherein the second source base station (606) shares resources with a first source base station (606) associated with the first PLMN or the first network slice and the resources shared by the first and second target base stations (600 and 602) and the resources shared by the first and second source base stations (604 and 606) comprise physical layer resources, Medium Access Control, MAC, layer resources, or both physical layer resources and MAC layer resources; and

sending (Fig. 5, step 10), to a shared distributed unit (608) of the first target base station (600) and the second target base station (602), a message that triggers transfer of the connection reestablishment request procedure from a distributed unit (610A) of the first target base station (600) to a distributed unit (610B) of the second target base station (600).

36. A central unit (612B) of a second target base station (606) associated with a second Public Land Mobile Network, PLMN, or a second network slice, for connection reestablishment for a User Equipment, UE, (600), wherein the second target base station (602) shares resources with a first target base station (600) associated with a first PLMN or a first network slice, the central unit (612 B) adapted to:

receive (Fig. 5, step 8) a UE context of the UE (620) from a central unit (618B) of a second source base station (606) associated with the second PLMN or the second network slice, wherein the second source base station (606) shares resources with a first source base station (606) associated with the first PLMN or the first network slice and the resources shared by the first and second target base stations (600 and 602) and the resources shared by the first and second source base stations (604 and 606) comprise physical layer resources, Medium Access Control, MAC, layer resources, or both physical layer resources and MAC layer resources; and

send (Fig. 5, step 10), to a shared distributed unit (608) of the first target base station (600) and the second target base station (602), a message that triggers transfer of the connection reestablishment request procedure from a distributed unit (610A) of the first target base station (600) to a distributed unit (610B) of the second target base station (600).

37. A node implementing a central unit (612B) of a second target base station (606) associated with a second Public Land Mobile Network, PLMN, or a second network slice, for connection reestablishment for a User Equipment (600), wherein the second target base station (602) shares resources with a first target base station (600) associated with a first PLMN or a first network slice, the node comprising:

a network interface; and

processing circuitry associated with the network interface, the processing circuitry configured to cause the node to:

receive (Fig. 5, step 8) a UE context of the UE (620) from a central unit (618B) of a second source base station (606) associated with the second PLMN or the second network slice, wherein the second source base station (606) shares resources with a first source base station (606) associated with the first PLMN or the first network slice and the resources shared by the first and second target base stations (600 and 602) and the resources shared by the first and second source base stations (604 and 606) comprise physical layer resources, Medium Access Control, MAC, layer resources, or both physical layer resources and MAC layer resources; and

send (Fig. 5, step 10), to a shared distributed unit (608) of the first target base station (600) and the second target base station (602), a message that triggers transfer of the connection reestablishment request procedure from a distributed unit (610A) of the first target base station (600) to a distributed unit (610B) of the second target base station (600).

Description:
REDIRECTION MECHANISM TO SUPPORT NETWORK SHARING/SLICING WITH CU-DU SPLIT FOR RE-ESTABLISHMENT

Related Applications

[0001] This application claims the benefit of provisional patent application serial number 62/760,658, filed November 13, 2018, the disclosure of which is hereby incorporated herein by reference in its entirety.

Technical Field

[0002] Systems and methods disclosed herein relate to network sharing or network slicing in a wireless network including base stations having a Centralized Unit (CU) / Distributed Unit (DU) split.

Background

[0003] Figure 1 depicts the current Fifth Generation (5G) Radio Access Network (RAN) architecture, as described in Third Generation Partnership Project (3GPP) Technical Specification (TS) 38.401 (see e.g., V15.3.0). The Next Generation (NG) architecture can be further described as follows. The NG-RAN consists of a set of NG Node Bs (gNBs) connected to a 5G Core Network (5GC) through an NG interface. A gNB can support Frequency Division Duplex (FDD) mode, Time Division Duplex (TDD) mode, or dual mode operation. gNBs can be interconnected through an Xn interface. A gNB may consist of a gNB Central Unit (gNB-CU) and gNB Distributed Units (gNB-DUs). A gNB-DU is connected to a gNB-CU via an FI logical interface. One gNB-DU is connected to only one gNB-CU.

[0004] NG, Xn, and FI are logical interfaces. For NG-RAN, the NG and Xn-C interfaces for a gNB consisting of a gNB-CU and gNB-DUs, terminate in the gNB-CU.

For Evolved Universal Terrestrial Radio Access Network (E-UTRAN) New Radio - Dual Connectivity (EN-DC), the Sl-U and X2-C interfaces for a gNB consisting of a gNB-CU and gNB-DUs, terminate in the gNB-CU. The gNB-CU and connected gNB-DUs are only visible to other gNBs and the 5GC as a gNB.

[0005] The NG-RAN is layered into a Radio Network Layer (RNL) and a Transport Network Layer (TNL). The NG-RAN architecture, e.g. the NG-RAN logical nodes and interfaces between them, is defined as part of the RNL. For each NG-RAN interface (NG, Xn, FI) the related TNL protocol and the functionality are specified. The TNL provides services for user plane transport and signaling transport. In NG-Flex configuration, each gNB is connected to all Access and Mobility Management Functions (AMFs) within an AMF Region. The AMF Region can be as defined in 3GPP TS 23.501 (see, e.g., V15.3.0).

[0006] The general principles for the specification of the FI interface are as follows:

• the FI interface is to be open;

• the FI interface supports the exchange of signaling information between the endpoints, in addition the interface shall support data transmission to the respective endpoints;

• from a logical standpoint, the FI is a point-to-point interface between the

endpoints (a point-to-point logical interface should be feasible even in the absence of a physical direct connection between the endpoints);

• the FI interface supports control plane and user plane separation;

• the FI interface separates RNL and TNL;

• the FI interface enable exchanges of User Equipment (UE) associated

information and non-UE associated information;

• the FI interface is defined to be future proof to fulfil different new requirements, support new services and new functions;

• one gNB-CU and set of gNB-DUs are visible to other logical nodes as a gNB. The gNB terminates X2, Xn, NG and Sl-U interfaces;

• the CU may be separated in Control Plane (CP) and User Plane (UP).

[0007] In regarding to network sharing, according to 3GPP TS 23.501 (see, e.g., V15.3.0) §5.18, 5G System (5GS) supports Multi Operator Core Network (MOCN) scenario, where several operators share RAN resources. As compared to MOCN defined for Third Generation (3G) and Fourth Generation (4G) (up to Release 13), there are two kinds of MOCN configurations:

1. single Cell Identity (ID) / Tracking Area Code (TAC) cell configuration, and

2. multiple Cell ID / TAC cell configuration.

[0008] Single Cell ID / TAC cell configuration refers to the "classical" MOCN configuration, which was defined up to Release 13 for 3G and 4G. Such configuration foresaw to share not only cell radio resources but also Cell IDs and TACs, i.e. the same value for a Cell ID / TAC was used by all operators, the cells and Tracking Areas (TAs) could be only distinguished globally, i.e. as Cell Group Identities (CGIs) or Tracking Area Identities (TAIs), with the Public Land Mobile Network (PLMN) ID prefix. This required operators to coordinate those IDs. Multiple Cell ID / TAC cell configuration is able to overcome those restrictions, and broadcast information associated with a single physical cell resource is able to indicate more than one Cell ID / TAC pair, each of which is associated with an operator's network.

[0009] The only deployment scenario for the single Cell ID / TAC cell configuration required and supported was the case where the RAN was owned by a single operator and offered to other operators. The resulting architecture was a single RAN connected to several core networks.

[0010] The multiple Cell ID / TAC cell configuration offers several possibilities, but the most common is one where several separate operator networks logically operate their own networks. This is very much in line with the intention of this configuration option. Operators have the benefit of configuring and operating their own network, independent from configuration and operating strategies of the networks of other operators. Actual sharing of physical cell resources would work as for the "classical" MOCN scenarios, where fixed or dynamic quotas would regulate the usage radio resources.

[0011] 3GPP is currently working on standardization of 5G CN and New Radio (NR) access. In this work there is a lot of focus to support network slicing. Below is a short description of network slicing.

[0012] The support for network slicing is an important part of the vision for the 5G System architecture. As stated by different fora, such as Next Generation Mobile Network (NGMN) Alliance, network slicing consists of deploying multiple end-to-end logical networks in support of independent business operations. In contrast to deploying an independent network infrastructure, each instance of a slice (blueprint) should be possible to realize as a logical network corresponding to a shared

infrastructure (including shared processing, storage, transport, radio spectrum, and hardware platforms), where it co-exists with other slices having potentially different characteristics. Figure 2 depicts an example of multiple slice instances deployed in the same network infrastructure. In this way, the infrastructure and assets utilization will be much more cost- and energy-efficient while the logical separation allows for a flexible and independent configuration and management of the slices without compromising stability and security. Enabling slice realization over a common physical infrastructure would of course not prevent the realization of a slice instance by means of dedicated resources and assets.

[0013] In 3GPP, the notion of network slicing has also been introduced as a way to address the needs for the different vertical industries, translated into a wide range of use cases for the Next Generation architecture. Network slicing is an end to end concept, where a given network slice could be made up of different dedicated or shared sub-network instances. For example, it is possible to deploy network supporting two slices using a shared RAN sub-network instance used by both slices and two dedicated core network sub-network instances for each slice. In this case the RAN would have a selection function connecting UEs of one slice to the correct core network instance.

[0014] Systems and methods for connection reestablishment in a cellular

communications system that utilizes Centralized Unit (CU) / Distributed Unit (DU) split and either network sharing or network slicing are disclosed. In one embodiment, a method performed by a shared distributed unit for connection reestablishment for a User Equipment (UE) is disclosed. The shared distributed unit comprises: (a) a distributed unit of a first target base station associated with a first Public Land Mobile Network (PLMN) or a first network slice and (b) a distributed unit of a second target base station associated with a second PLMN or a second network slice, wherein the first target base station and the second target base station share resources. The method comprises receiving, from the UE at the distributed unit of the first target base station, a connection reestablishment request comprising an identity of the UE in a source cell to which the UE was connected prior to sending the connection reestablishment request and an identity of the source cell. The method further comprises sending an initial message to a central unit of the first target base station, the initial message comprising: (a) the identity of the UE in the source cell, (b) the identity of the source cell, and (c) information regarding a second cell served by the second target base station using the shared resources, wherein the shared resources comprise physical layer resources, Medium Access Control (MAC) layer resources, or both physical layer resources and MAC layer resources. Using this information, UE context retrieval for the connection reestablishment procedure can be redirected to a correct central unit. [0015] In some embodiments, the connection reestablishment request is a Radio Resource Control (RRC) Reestablishment Request.

[0016] In some embodiments, the information regarding the second cell served by the second target base station using the shared physical layer and/or MAC layer resources comprises a Cell Group Identifier (CGI) of the second cell, a PLMN identity (ID) of the second PLMN associated with the second cell, or both a CGI of the second cell and the PLMN ID of the second PLMN associated with the second cell.

[0017] In some embodiments, the initial message comprises at least a portion of the connection reestablishment request.

[0018] In some embodiments, the method further comprises receiving, from a central unit of the second target base station, a message that transfers the connection reestablishment procedure for the UE from the distributed unit of the first target base station to the distributed unit of the second target base station, and completing the connection reestablishment procedure.

[0019] Embodiments of a shared distribution unit for connection reestablishment for a UE are also disclosed. In some embodiments, the shared distributed unit comprises: (a) a distributed unit of a first target base station associated with a first PLMN or a first network slice and (b) a distributed unit of a second target base station associated with a second PLMN or a second network slice, wherein the first target base station and the second target base station share resources. The shared distributed unit is adapted to receive, from the UE at the distributed unit of the first target base station, a connection reestablishment request comprising an identity of the UE in a source cell to which the UE was connected prior to sending the connection reestablishment request and an identity of the source cell. The shared distribution unit is further adapted to send an initial message to a central unit of the first target base station, the initial message comprising: (a) the identity of the UE in the source cell, (b) the identity of the source cell, and (c) information regarding a second cell served by the second target base station using the shared resources, wherein the shared resources comprise physical layer resources, MAC layer resources, or both physical layer resources and MAC layer resources.

[0020] Embodiments of a node implementing a shared distributed unit for connection reestablishment for a UE are also disclosed. In some embodiments, the shared distributed unit comprises: (a) a distributed unit of a first target base station associated with a first PLMN or a first network slice and (b) a distributed unit of a second target base station associated with a second PLMN or a second network slice, wherein the first target base station and the second target base station share resources. The node comprises a network interface and processing circuitry associated with the network interface. The processing circuitry is configured to cause the node to receive, from the UE at the distributed unit of the first target base station, a connection reestablishment request comprising an identity of the UE in a source cell to which the UE was connected prior to sending the connection reestablishment request and an identity of the source cell. The processing circuitry is further configured to cause the node to send an initial message to a central unit of the first target base station, the initial message comprising: (a) the identity of the UE in the source cell, (b) the identity of the source cell, and (c) information regarding a second cell served by the second target base station using the shared resources, wherein the shared resources comprise physical layer resources, MAC layer resources, or both physical layer resources and MAC layer resources.

[0021] Embodiments of a method performed by a central unit of a first target base station associated with a first PLMN or a first network slice for a connection

reestablishment procedure for a UE are also disclosed. The first target base station shares resources with a second target base station associated with a second PLMN or a second network slice. The method comprises receiving an initial message from a shared distributed unit of the first target base station and the second target base station. The initial message comprises: (a) an identity of the UE in a source cell to which the UE was connected prior to sending a connection reestablishment request that triggered the initial message, (b) the identity of the source cell, and (c) information regarding a second cell served by the second target base station using the shared resources, wherein the shared resources comprise physical layer resources, MAC layer resources, or both physical layer resources and MAC layer resources. The method further comprises sending, to a central unit of a first source base station associated with the first PLMN or the first network slice, a request to retrieve a UE context of the UE. The request comprises the identity of the UE in the source cell, the identity of the source cell, and the information regarding the second cell served by the second target base station using the shared resources. Using this information, UE context retrieval for the connection reestablishment procedure can be redirected to a correct central unit. [0022] In some embodiments, the connection reestablishment request is a RRC Reestablishment Request.

[0023] In some embodiments, the information regarding the second cell served by the second target base station using the shared resources comprises a CGI of the second cell, a PLMN ID of the second PLMN associated with the second cell, or both a CGI of the second cell and the PLMN ID of the second PLMN associated with the second cell.

[0024] In some embodiments, both the initial message and the request comprise at least a portion of the connection reestablishment request.

[0025] Embodiments of a central unit of a first target base station associated with a first PLMN or a first network slice for a connection reestablishment procedure for a UE are also disclosed. In some embodiments, the first target base station shares resources with a second target base station associated with a second PLMN or a second network slice, and the central unit is adapted to receive an initial message from a shared distributed unit of the first target base station and the second target base station. The initial message comprises: (a) an identity of the UE in a source cell to which the UE was connected prior to sending a connection reestablishment request that triggered the initial message, (b) the identity of the source cell, and (c) information regarding a second cell served by the second target base station using the shared resources, wherein the shared resources comprise physical layer resources, MAC layer resources, or both physical layer resources and MAC layer resources. The central unit is further adapted to send, to a central unit of a first source base station associated with the first PLMN or the first network slice, a request to retrieve a UE context of the UE. The request comprising the identity of the UE in the source cell, the identity of the source cell, and the information regarding the second cell served by the second target base station using the shared resources. Using this information, UE context retrieval for the connection reestablishment procedure can be redirected to a correct central unit.

[0026] Embodiments of a node implementing a central unit of a first target base station associated with a first PLMN or a first network slice for a connection

reestablishment procedure for a UE are also disclosed. In some embodiments, the first target base station shares resources with a second target base station associated with a second PLMN or a second network slice, and the node comprises a network interface and processing circuitry associated with the network interface. The processing circuitry is configured to cause the node to receive an initial message from a shared distributed unit of the first target base station and the second target base station. The initial message comprises: (a) an identity of the UE in a source cell to which the UE was connected prior to sending a connection reestablishment request that triggered the initial message, (b) the identity of the source cell, and (c) information regarding a second cell served by the second target base station using the shared resources, wherein the shared resources comprise physical layer resources, MAC layer resources, or both physical layer resources and MAC layer resources. The processing circuitry is further configured to cause the node to send, to a central unit of a first source base station associated with the first PLMN or the first network slice, a request to retrieve a UE context of the UE. The request comprises the identity of the UE in the source cell, the identity of the source cell, and the information regarding the second cell served by the second target base station using the shared resources.

[0027] Embodiments of a method performed by a central unit of a first source base station associated with a first PLMN or a first network slice for a connection

reestablishment procedure for a UE are also disclosed. In some embodiments, the first source base station shares resources with a second source base station associated with a second PLMN or a second network slice, and the method comprises receiving, from a central unit of a first target base station associated with the first PLMN or the first network slice, a request to retrieve a UE context of the UE. The request comprises: (a) an identity of the UE in a source cell to which the UE was connected prior to connection reestablishment, (b) the identity of the source cell, and (c) information regarding a second cell served by a second target base station that shares resources with the first target base station, wherein the resources shared by the first and second source base stations and the resources shared by the first and second target base stations comprise physical layer resources, MAC layer resources, or both physical layer resources and MAC layer resources. The method further comprises determining that the UE context of the UE cannot be found by the central unit of the first source base station. The method further comprises, upon determining that the UE context of the UE cannot be found, sending a message to a shared distributed unit of the first source base station and the second source base station that allocated the identity of the UE in the source cell to initiate redirection of the request to retrieve the UE context of the UE to a correct central unit of the second source base station. [0028] In some embodiments, the request to retrieve the UE context of the UE further comprises at least a portion of a connection reestablishment request message sent by the UE to initiate the connection reestablishment procedure.

[0029] In some embodiments, the message sent to the shared distributed unit of the first source base station and the second source base station that allocated the identity of the UE in the source cell comprises: (a) the identity of the UE in the source cell, (b) at least a portion of a connection reestablishment request message sent by the UE to initiate the connection reestablishment procedure, (c) at least a portion of the request to retrieve the UE context of the UE, (d) the information regarding the second cell served by the second target base station using the shared resources, or (e) any combination of two or more of (a) - (d).

[0030] In some embodiments, the information regarding the second cell served by the second target base station using the shared resources comprises a CGI of the second cell, a PLMN ID of the second PLMN associated with the second cell, or both the CGI of the second cell and the PLMN ID of the second PLMN associated with the second cell.

[0031] Embodiments of a central unit of a first source base station associated with a first PLMN or a first network slice for a connection reestablishment procedure for a UE are also disclosed. In some embodiments, the first source base station shares resources with a second source base station associated with a second PLMN or a second network slice, and the central unit is adapted to receive, from a central unit of a first target base station associated with the first PLMN or the first network slice, a request to retrieve a UE context of the UE. The request comprises: (a) an identity of the UE in a source cell to which the UE was connected prior to connection reestablishment, (b) the identity of the source cell, and (c) information regarding a second cell served by a second target base station that shares resources with the first target base station, wherein the resources shared by the first and second source base stations and the resources shared by the first and second target base stations comprise physical layer resources, MAC layer resources, or both physical layer resources and MAC layer resources. The central unit is further adapted to determine that the UE context of the UE cannot be found by the central unit of the first source base station and, upon determining that the UE context of the UE cannot be found, send a message to a shared distributed unit of the first source base station and the second source base station that allocated the identity of the UE in the source cell to initiate redirection of the request to retrieve the UE context of the UE to a correct central unit of the second source base station.

[0032] Embodiments of a node implementing a central unit of a first source base station associated with a first PLMN or a first network slice for a connection

reestablishment procedure for a UE are also disclosed. In some embodiments, the first source base station shares resources with a second source base station associated with a second PLMN or a second network slice, and the node comprises a network interface and processing circuitry associated with the network interface. The processing circuitry is configured to cause the node to receive, from a central unit of a first target base station associated with the first PLMN or the first network slice, a request to retrieve a UE context of the UE. The request comprises: (a) an identity of the UE in a source cell to which the UE was connected prior to connection reestablishment, (b) the identity of the source cell, and (c) information regarding a second cell served by a second target base station that shares resources with the first target base station, wherein the resources shared by the first and second source base stations and the resources shared by the first and second target base stations comprise physical layer resources, MAC layer resources, or both physical layer resources and MAC layer resources. The processing circuitry is further configured to cause the node to determine that the UE context of the UE cannot be found by the central unit of the first source base station and, upon determining that the UE context of the UE cannot be found, send a message to a shared distributed unit of the first source base station and the second source base station that allocated the identity of the UE in the source cell to initiate redirection of the request to retrieve the UE context of the UE to a correct central unit of the second source base station.

[0033] Embodiments of a method performed by a second shared distributed unit of: (a) a first source base station associated with a first PLMN or a first network slice, (b) the identity of the source cell, and (c) a second source base station associated with a second PLMN or a second network slice, for a connection reestablishment procedure for a UE are disclosed. In some embodiments, the first source base station and the second source base station share resources, and the method comprises receiving, from a central unit of the first source base station, a message to initiate redirection of a request to retrieve a UE context of the UE to a correct central unit. The message comprises: (a) an identity of the UE in a source cell to which the UE was connected prior to connection reestablishment and (b) information regarding a second cell served by a second target base station associated with the second PLMN or the second network slice that shares resources with a first target base station associated with the first PLMN or the first network slice, wherein the resources shared by the first and second source base stations and the resources shared by the first and second target base stations comprise physical layer resources, MAC layer resources, or both physical layer resources and MAC layer resources. The method further comprises identifying a correct central unit of the second source base station from which to retrieve the UE context of the UE based on the message to initiate redirection of the request to retrieve the UE context of the UE, and sending, to the correct central unit of the second source base station, a message that redirects the request to retrieve the UE context of the UE to the correct central unit of the second source base station.

[0034] In some embodiments, the message to initiate redirection of the request to receive a UE context of the UE comprises the identity of the UE in the source cell and the information regarding the second cell served by the second target base station.

[0035] In some embodiments, the message to initiate redirection of the request to receive a UE context of the UE comprises at least a portion of a connection

reestablishment request transmitted by the UE to initiate connection reestablishment.

[0036] In some embodiments, the message that redirects the request to retrieve the UE context of the UE comprises the identity of the UE in the source cell and the information regarding the second cell served by the second target base station using the shared resources.

[0037] In some embodiments, the message that redirects the request to retrieve the UE context of the UE comprises at least a portion of a connection reestablishment request transmitted by the UE to initiate connection reestablishment.

[0038] In some embodiments, the information regarding the second cell served by the second target base station using the shared resources comprises a CGI of the second cell, a PLMN ID of the second PLMN associated with the second cell, or both the CGI of the second cell and the PLMN ID of the second PLMN associated with the second cell.

[0039] Embodiments of a second shared distributed unit of: (a) a first source base station associated with a first PLMN or a first network slice and (b) a second source base station associated with a second PLMN or a second network slice, for a connection reestablishment procedure for a UE are also disclosed. In some embodiments, the first source base station and the second source base station share resources, and the second shared distributed unit is adapted to receive, from a central unit of the first source base station, a message to initiate redirection of a request to retrieve a UE context of the UE to a correct central unit. The message comprises: (a) an identity of the UE in a source cell to which the UE was connected prior to connection

reestablishment, (b) the identity of the source cell, and (c) information regarding a second cell served by a second target base station associated with the second PLMN or the second network slice that shares resources with a first target base station

associated with the first PLMN or the first network slice, wherein the resources shared by the first and second source base stations and the resources shared by the first and second target base stations comprise physical layer resources, MAC layer resources, or both physical layer resources and MAC layer resources. The second shared distributed unit is further adapted to identify a correct central unit of the second source base station from which to retrieve the UE context of the UE based on the message to initiate redirection of the request to retrieve the UE context of the UE, and send, to the correct central unit of the second source base station, a message that redirects the request to retrieve the UE context of the UE to the correct central unit of the second source base station.

[0040] Embodiments of a node implementing a second shared distributed unit of: (a) a first source base station associated with a first PLMN or a first network slice and (b) a second source base station associated with a second PLMN or a second network slice, for a connection reestablishment procedure for a UE are also disclosed. In some embodiments, the first source base station and the second source base station share resources, and the node comprises a network interface and processing circuitry associated with the network interface. The processing circuitry configured to cause the node to receive, from a central unit of the first source base station, a message to initiate redirection of a request to retrieve a UE context of the UE to a correct central unit. The message comprises: (a) an identity of the UE in a source cell to which the UE was connected prior to connection reestablishment, (b) the identity of the source cell, and (c) information regarding a second cell served by a second target base station associated with the second PLMN or the second network slice that shares resources with a first target base station associated with the first PLMN or the first network slice, wherein the resources shared by the first and second source base stations and the resources shared by the first and second target base stations comprise physical layer resources, MAC layer resources, or both physical layer resources and MAC layer resources. The processing circuitry is further configured to cause the node to identify a correct central unit of the second source base station from which to retrieve the UE context of the UE based on the message to initiate redirection of the request to retrieve the UE context of the UE, and send, to the correct central unit of the second source base station, a message that redirects the request to retrieve the UE context of the UE to the correct central unit of the second source base station.

[0041] Embodiments of a method performed by a central unit of a second source base station associated with a second PLMN or a second network slice for a connection reestablishment procedure for a UE are also disclosed. In some embodiments, the second source base station shares resources with a first source base station associated with a first PLMN or a first network slice, and the method comprises receiving, from a shared distributed unit of the first source base station and the second source base station, a message that redirects a request to retrieve a UE context of the UE to the central unit of the second source base station. The method further comprises, upon receiving the message, retrieving the UE context of the UE, and sending the UE context of the UE to a central unit of a second target base station associated with the second PLMN or the second network slice that shares resources with a first target base station associated with the first PLMN or the first network slice, wherein the central unit of the second target base station is associated with a shared distributed unit of the first target base station and the second target base station at which a respective connection reestablishment request was received from the UE.

[0042] In some embodiments, the message that redirects the request to retrieve the UE context of the UE comprises the identity of the UE in the source cell and the information regarding the second cell served by the second target base station using the shared resources.

[0043] In some embodiments, the message that redirects the request to retrieve the UE context of the UE comprises at least a portion of the connection reestablishment request from the UE. [0044] In some embodiments, the information regarding the second cell served by the second target base station using the shared resources comprises a CGI of the second cell, a PLMN ID of the second PLMN associated with the second cell, or both the CGI of the second cell and the PLMN ID of the second PLMN associated with the second cell.

[0045] Embodiments of a central unit of a second source base station associated with a second PLMN or a second network slice for a connection reestablishment procedure for a UE are also disclosed. In some embodiments, the second source base station shares resources with a first source base station associated with a first PLMN or a first network slice, and the central unit is adapted to receive, from a shared

distributed unit of the first source base station and the second source base station, a message that redirects a request to retrieve a UE context of the UE to the central unit of the second source base station. The central unit is further adapted to, upon receiving the message, retrieve the UE context of the UE, and send the UE context of the UE to a central unit of a second target base station associated with the second PLMN or the second network slice that shares resources with a first target base station associated with the first PLMN or the first network slice, wherein the central unit of the second target base station is associated with a shared distributed unit of the first target base station and the second target base station at which a respective connection

reestablishment request was received from the UE.

[0046] Embodiments of a node implementing a central unit of a second source base station associated with a second PLMN or a second network slice for a connection reestablishment procedure for a UE are also disclosed. In some embodiments, the second source base station shares resources with a first source base station associated with a first PLMN or a first network slice, and the node comprises a network interface and processing circuitry associated with the network interface. The processing circuitry is configured to cause the node to receive, from a shared distributed unit of the first source base station and the second source base station, a message that redirects a request to retrieve a UE context of the UE to the central unit of the second source base station. The processing circuitry is further configured to cause the node to, upon receiving the message, retrieve the UE context of the UE, and send the UE context of the UE to a central unit of a second target base station associated with the second PLMN or the second network slice that shares resources with a first target base station associated with the first PLMN or the first network slice, wherein the central unit of the second target base station is associated with a shared distributed unit of the first target base station and the second target base station at which a respective connection reestablishment request was received from the UE.

[0047] Embodiments of a method performed by a central unit of a second target base station associated with a second PLMN or a second network slice, for connection reestablishment for a UE are also disclosed. In some embodiments, the second target base station shares resources with a first target base station associated with a first PLMN or a first network slice, and the method comprises receiving a UE context of the UE from a central unit of a second source base station associated with the second PLMN or the second network slice. The second source base station shares resources with a first source base station associated with the first PLMN or the first network slice and the resources shared by the first and second target base stations, and the resources shared by the first and second source base stations comprise physical layer resources, MAC layer resources, or both physical layer resources and MAC layer resources. The method further comprises sending, to a shared distributed unit of the first target base station and the second target base station, a message that triggers transfer of the connection reestablishment request procedure from a distributed unit of the first target base station to a distributed unit of the second target base station.

[0048] Embodiments of a central unit of a second target base station associated with a second PLMN or a second network slice, for connection reestablishment for a UE are also disclosed. In some embodiments, the second target base station shares resources with a first target base station associated with a first PLMN or a first network slice, and the central unit is adapted to receive a UE context of the UE from a central unit of a second source base station associated with the second PLMN or the second network slice, wherein the second source base station shares resources with a first source base station associated with the first PLMN or the first network slice and the resources shared by the first and second target base stations and the resources shared by the first and second source base stations comprise physical layer resources, MAC layer resources, or both physical layer resources and MAC layer resources. The central unit is further adapted to send, to a shared distributed unit of the first target base station and the second target base station, a message that triggers transfer of the connection reestablishment request procedure from a distributed unit of the first target base station to a distributed unit of the second target base station.

[0049] Embodiments of a node implementing a central unit of a second target base station associated with a second PLMN or a second network slice, for connection reestablishment for a UE, are also disclosed. In some embodiments, the second target base station shares resources with a first target base station associated with a first PLMN or a first network slice, and the node comprises a network interface and processing circuitry associated with the network interface. The processing circuitry is configured to cause the node to receive a UE context of the UE from a central unit of a second source base station associated with the second PLMN or the second network slice, wherein the second source base station shares resources with a first source base station associated with the first PLMN or the first network slice and the resources shared by the first and second target base stations and the resources shared by the first and second source base stations comprise physical layer resources, MAC layer resources, or both physical layer resources and MAC layer resources. The processing circuitry is further configured to cause the node to send, to a shared distributed unit of the first target base station and the second target base station, a message that triggers transfer of the connection reestablishment request procedure from a distributed unit of the first target base station to a distributed unit of the second target base station.

[0050] Embodiments of a method performed for connection reestablishment of a UE in a cellular communications system are also disclosed. In some embodiments, the method comprises, at a shared distributed unit that comprises: (a) a distributed unit of a first target base station associated with a first PLMN or a first network slice and (b) a distributed unit of a second target base station associated with a second PLMN or a second network slice, wherein the first target base station and the second target base station share resources, receiving, from the UE at the distributed unit of the first target base station, a connection reestablishment request comprising an identity of the UE in a source cell to which the UE was connected prior to sending the connection

reestablishment request and an identity of the source cell. The method further comprises, at the shared distributed unit, sending an initial message to a central unit of the first target base station, the initial message comprising: (a) the identity of the UE in the source cell, (b) the identity of the source cell, and (c) information regarding a second cell served by the second target base station using the shared resources, wherein the shared resources comprise physical layer resources, MAC layer resources, or both physical layer resources and MAC layer resources. The method further comprises, at the central unit of the first target base station, receiving the initial message from the shared distributed unit of the first target base station and the second target base station and sending, to a central unit of a first source base station associated with the first PLMN or the first network slice, a request to retrieve a UE context of the UE. The request comprises the identity of the UE in the source cell, the identity of the source cell, and the information regarding the second cell served by the second target base station using the shared resources. The method further comprises, at the central unit of the first source base station, wherein the first source base station shares resources with a second source base station associated with a second PLMN or a second network slice and the resources shared by the first and second target base stations comprise physical layer resources, MAC layer resources, or both physical layer resources and MAC layer resources, receiving the request to retrieve the UE context of the UE from the central unit of the first target base station. The method further comprises, at the central unit of the first source base station, determining that the UE context of the UE cannot be found by the central unit of the first source base station and, upon determining that the UE context of the UE cannot be found, sending a message to a shared distributed unit of the first source base station and the second source base station that allocated the identity of the UE in the source cell to initiate redirection of the request to retrieve the UE context of the UE to a correct central unit of the second source base station. The method further comprises, at the second shared distributed unit, receiving, from the central unit of the first source base station, the message to initiate redirection of the request to retrieve the UE context of the UE to a correct central unit. The method further comprises, at the second shared distributed unit, identifying a correct central unit of the second source base station from which to retrieve the UE context of the UE based on the message to initiate redirection of the request to retrieve the UE context of the UE, and sending, to the correct central unit of the second source base station, a message that redirects the request to retrieve the UE context of the UE to the correct central unit of the second source base station. The method further comprises, at the correct central unit of the second source base station, receiving, from the shared distributed unit of the first source base station and the second source base station, the message that redirects the request to retrieve the UE context of the UE to the central unit of the second source base station. The method further comprises, at the correct central unit of the second source base station, upon receiving the message, retrieving the UE context of the UE, and sending the UE context of the UE to a central unit of the second target base station, wherein the central unit of the second target base station is associated with the shared distributed unit of the first target base station and the second target base station at which the connection reestablishment request was received from the UE. The method further comprises, at the central unit of the second target base station, receiving the UE context of the UE from the correct central unit of the second source base station, and sending, to the shared distributed unit of the first target base station and the second target base station, a message that triggers transfer of the connection reestablishment request procedure from the distributed unit of the first target base station to the distributed unit of the second target base station.

Brief Description of the Drawings

[0051] The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the

description serve to explain the principles of the disclosure.

[0052] Figure 1 depicts the current Fifth Generation (5G) Radio Access Network (RAN) architecture, as described in Third Generation Partnership Project (3GPP)

Technical Specification (TS) 38.401 (see e.g., V15.3.0);

[0053] Figure 2 depicts an example of multiple slice instances deployed in the same network infrastructure;

[0054] Figure 3 illustrates an example split Centralized Unit (CU) / Distributed Unit (DU) deployment that uses networking sharing;

[0055] Figure 4 illustrates an example split CU/DU deployment that uses network slices;

[0056] Figure 5 shows one example of a Radio Resource Control (RRC)

Reestablishment procedure using a split CU/DU architecture with network sharing, in accordance with some embodiments of the present disclosure;

[0057] Figure 6 illustrates the split CU/DU architecture used by the RRC

Reestablishment procedure of Figure 5; [0058] Figure 7 illustrates an example of a system in which embodiments of the present disclosure may be implemented;

[0059] Figure 8 illustrates one embodiment of a UE in accordance with various aspects described herein; and

[0060] Figure 9 is a schematic block diagram illustrating a virtualization environment in which functions implemented by some embodiments may be virtualized.

[0061] The embodiments set forth below represent information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure.

[0062] There currently exist certain challenges with respect to network sharing in the current Next Generation (NG) Radio Access Network (RAN) (i.e., NG-RAN) architecture. It could be beneficial to combine network sharing scenarios using multiple Cell Identity (ID) / Tracking Area Code (TAC) cell configuration with NG Node B (gNB) Centralized Unit (CU) / Distributed Unit (DU) split deployments. In this case, deployments may keep the possibility of separating CUs (also referred to herein as gNB-CUs)

geographically from each other. Thus, it cannot be always assumed that CUs that operate in network sharing would be able to exchange data easily due to their geographical separation, not to speak of security issues in doing so. Flowever, it can be assumed that a single physical DU (also referred to herein as gNB-DU) will be deployed in such scenarios, such that at least the Physical (PFIY) layer and Medium Access Control (MAC) layer would need to be a common resource, with implementation specific means to follow quotas negotiated among sharing partners.

[0063] Figure 3 shows such a deployment. It is assumed that the logical Public Land Mobile Network (PLMN) specific gNB-DUs and the common PHY/MAC box, schematically shown, are in one physical entity, whereas gNB-CUs are separate from each other. It is also shown that one PLMN specific gNB-CU and gNB-DU and the PHY/MAC entity form one logical gNB. In other words, in the example of Figure 3, there are three PLMNs, which are denoted as PLM NA, PLM NB, and PLMNc. PLMNA, PLMNB, and PLMNc have respective logical gNBs, which are denoted as gNB A , gNB e , and gNB c , connected to respective Fifth Generation Core Networks (5GCs), which are denoted as 5GCA, 5GCB, and 5GCc. As illustrated, the three logical gNBs have respective TACs, denoted as TAC a , TACB, and TACc, and respective cell IDs, denoted as CellID A , CellID B , and CelllDc. The three logical gNBs include separate gNB-CUs, which are denoted as CU A , CU B , and CUc, having respective FI interfaces to respective gNB-DUs, which are denoted as DUA, DUB, and DUc. The gNB-DUs share common cell resources and schedulers (e.g., common PFIY and MAC). Note that the physical implementation of the entity that includes the gNB-DUs and the shared PFIY and MAC layer resources is sometimes referred to herein as a "shared gNB-DU" (e.g., shared gNB-DU A / B /c)· So, the shared gNB-DU having the PFIY and MAC layer resources provides the gNB-DU A , the gNB-DU B , and the gNB-DUc with necessary data for sending it via FI to the respective gNB-CUs (i.e., gNB-CU A , gNB- CU B , and gNB-CU c ). The gNB-DU A , the gNB-DU e , and the gNB-DU c are "pure" FI protocol termination points, where the shared gNB-DU is the actual actuator when it comes to communicating with the UE. In general, it can also be assumed that the PLMN specific CUs are not inter-connected, nor are the 5GC nodes.

[0064] In the deployment scenario in Figure 3, each gNB-CU serves a specific PLMN (or a subset of PLMNs). This deployment scenario is not fully supported by the current Third Generation Partnership Project (3GPP) specifications. Specifically, there is no proper support for the following procedures:

• RRC Reestablishment: At Radio Resource Control (RRC) Reestablishment, the User Equipment (UE) sends an RRC Reestablishment Request message to the gNB-DU. The gNB-DU is then supposed to select the correct gNB-CU for the UE i.e., a gNB-CU that serves the PLMN selected by the UE. However, the RRC Reestablishment Request message does not include a PLMN ID. Therefore, the gNB-DU may send the RRC Reestablishment Request message to the wrong gNB- CU i.e., a gNB-CU that does not serve the PLMN selected by the UE. The wrong gNB-CU will then try to retrieve the UE context, but it will inevitably fail. The wrong gNB-CU will then try to send an RRC Setup message to the UE i.e., it will fail the RRC Re-establishment procedure and revert to an Initial Attach

procedure. [0065] The problem above is also valid in other cases where the operator wants to support multiple gNB-CUs, e.g. in deployments using network slices where different core network instances are deployed for different end to end slices and there is a desire to deploy different gNB-CU instances for each slice possible co-located with the core network instance. In this case, the network slices can utilize the same physical

(hardware (HW) / software (SW)) resources. An example of such scenario is depicted in Figure 4. In other words, in the example of Figure 4, there are three slices, which are denoted as slice A, slice B, and slice C, and corresponding logical gNBs, which are denoted as gNB A , gNB e , and gNBc, connected to respective 5GC instances, which are denoted as 5GC A , 5GC B , and 5GCc. As illustrated, the three logical gNBs include separate gNB-CUs, which are denoted as CU A , CUB, and CUc, having respective FI interfaces to respective gNB-DUs, which are denoted as DU A , DUB, and DUc. The gNB- DUs share common cell resources and scheduler (e.g., common PFIY and MAC). In this case, instead of PLMN ID, the UE would use a slice ID or a slice selection assistance information (Single Network Slice Selection Assistance Information (S-NSSAI)) as described below:

• RRC Reestablishment: At RRC Reestablishment, the UE sends an RRC

Reestablishment Request message to the gNB-DU. The gNB-DU is then supposed to select the correct gNB-CU for the UE i.e., a gNB-CU that serves the slice selected by the UE. Flowever, the RRC Reestablishment Request message does not include a Slice ID. Therefore, the gNB-DU may send the RRC

Reestablishment Request message to the wrong gNB-CU i.e., a gNB-CU that does not serve the Slice selected by the UE. The wrong gNB-CU will then try to retrieve the UE context, but it will inevitably fail. The wrong gNB-CU will then try to send an RRC Setup message to the UE i.e., it will fail the RRC Re ¬ establishment procedure and revert to an Initial Attach procedure.

[0066] Certain aspects of the present disclosure and their embodiments may provide solutions to these or other challenges. Embodiments of a solution to the

aforementioned problem(s) with the RRC Reestablishment procedure are disclosed herein. One example embodiment is as follows. If the UE was served by shared radio resources in an old cell (which is also referred to herein as the source cell or the cell to which the UE was connected prior to RRC reestablishment) and a wrong old RAN node (e.g., a wrong old gNB-CU, which is also referred to herein as a wrong source gNB-CU) is chosen at RRC reestablishment, this wrong old RAN node / old gNB-CU contacts the shared radio equipment that allocated the Cell Radio Network Temporary Identifier (C- RNTI) (e.g., the (correct) old gNB-DU, which is also referred to herein as the (correct) source gNB-DU) to redirect a context retrieval message to the correct old gNB-CU. Note that the correct old gNB-CU is the gNB-CU that served the UE before re-establishment.

A context retrieval result is then provided to a (correct) new RAN node (e.g., a (correct) new gNB-CU, which is also referred to herein as a (correct) target gNB-CU for RRC re ¬ establishment). The new RAN node communicates with a (correct) new gNB-DU for the RRC re-establishment and the UE, as if the new RAN node had received the

RRCReestablishmentRequest message from the new gNB-DU. Alternatively, instead of redirecting the UE context retrieval via the old gNB-DU, the first UE context retrieval could fail with an indication of the proper PLMN ID that the UE was served by before re ¬ establishment. A similar process may be used for RRC reestablishment with network slices.

[0067] Embodiments of the present disclosure provide a deterministic solution, which is not based on trial-and-error, for the case where the old cell (i.e., the source cell to which the UE was connected prior to RRC reestablishment) and the new cell (i.e., the target cell to which the UE is attempting to connect to via the RRC reestablishment) are shared by the same sharing operator(s). An example of this deterministic solution is as follows. The UE provides its old C-RNTI / Physical Cell Identity (PCI) to a new shared gNB-DU when requesting RRC reestablishment. The old shared gNB-DU may have stored a mapping between the old C-RNTI / PCI of the UE and a corresponding PLMN- specific old gNB-CU. The old shared gNB-DU would then be able to identify, in a deterministic way, the correct old gNB-CU, without the need of a trial/error procedure. The UE context can be retrieved from the correct old gNB-CU.

[0068] In some embodiments, a new solution for re-establishment is provided that supports network sharing and/or network slicing with CU-DU split, where different logical CUs and DUs share the same physical radio resources.

[0069] Certain embodiments may provide one or more of the following technical advantage(s). The proposed mechanism supports network sharing and/or network slicing with CU-DU split, where different logical CUs and DUs share the same physical radio resources. [0070] Figure 5 shows one example of a RRC Reestablishment procedure in accordance with some embodiments of the present disclosure. Note that this example is for an architecture such as that illustrated in Figure 3 that supports network sharing with CU-DU split, where different logical gNB-CUs and gNB-DUs share the same physical radio resources and where the different logical gNB-CUs and gNB-DUs are associated with different PLMN IDs. A similar process can be used for the architecture of Figure 4 that supports network slicing with CU-DU split, where different logical gNB-CUs and gNB-DUs share the same physical radio resources and where the different logical gNB- CUs and gNB-DUs are associated with different network slices.

[0071] Before describing the process of Figure 5 in detail, Figure 6 illustrates the architecture used in the process of Figure 5. As illustrated in Figure 6, in general, the RRC Reestablishment procedure of Figure 5 involves a new (i.e., target) gNB A 600, a new (i.e., target) gNB e 602, an old (i.e., source) gNB A 604, and an old (i.e., source) gNB e 606. The new gNB A 600 and the new gNB e 602 share PFIY and MAC layer resources as described above. As such, the new gNB A 600 and the new gNB e 602 include a new (i.e., target) shared gNB-DU A / B 604 that includes a new (i.e., target) gNB- DU A 610A, a new (i.e., target) gNB-DU B 610B, and shared PFIY and MAC layer

resources. The new gNB A 600 also includes a new (i.e., target) gNB-CU A 612A that, e.g., communicates with the new gNB-DU A 610A via an FI interface. Likewise, the new gNB e 602 also includes a new (i.e., target) gNB-CU B 612B that, e.g., communicates with the new gNB-DU B 610B via an FI interface. The old gNB A 604 and the old gNB B 606 also share PHY and MAC layer resources as described above. As such, the old gNB A 604 and the old gNB e 606 include an old (i.e., source) shared gNB-DU A / B 614 that includes an old (i.e., source) gNB-DU A 616A, an old (i.e., source) gNB-DU B 616B, and shared PHY and MAC layer resources. The old gNB A 604 also includes an old (i.e., source) gNB-CU A 618A that, e.g., communicates with the old gNB-DU A 616A via an FI interface. Likewise, the old gNB e 602 also includes an old (i.e., source) gNB-CU e 618B that, e.g., communicates with the old gNB-DU B 616B via an FI interface. Figure 5 illustrates a RRC reestablishment procedure in which a UE 620 sends an

RRCReestabHshmentRequest that is received by the new gNB-DU 610A within the new shared gNB-DU A / B 608.

[0072] Returning to Figure 5, as illustrated in Figure 5, the RRC Reestablishment procedure includes the following steps: • Step 1: The UE 620 sends an RRCReestabHshmentRequest to the new shared gNB-DU A / B 608. Within the new shared gNB-DU A / B 608, the

RRCReestabHshmentRequest \s more specifically received by the new shared gNB-DU A / B 608 and processed by the new shared gNB-DU A / B 608 -either in association with the new gNB-DU A 610A, which is a part of the new gNB A 600 that is associated with a first PLMN ID (PLM NA), or in association with the new gNB-DU B 610B, which is part of the new gNB e 602 that is associated with a second PLMN ID (PLM NB) . In this example, the RRCReestabHshmentRequest \s received by the new shared gNB-DU A / B 608 and processed by the new shared gNB-DU A / B 608 in association with the new gNB-DU A 610A, which is part of the new gNB A 600. Further, in this example, the RRCReestabHshmentRequest includes the following information:

o Information that identifies the UE 620, which is referred to as a "UE

Identity". In this example, the UE-Identity is a C-RNTI of the UE 620 for a cell to which the UE 620 was connected prior to RRC reestablishment.

This cell is referred to herein as a "source cell" or "old cell" of the UE 620. o A source PCI of the source cell of the UE 620.

o A short Message Authentication Code for Integrity (MAC-I) for security algorithms.

o A reestablishmentCause that indicates a cause of the RRC reestablishment request. Some example causes are reconfiguration failure, handover failure, or some other failure.

• Step 2: The new shared gNB-DU A / B 608 (and in particular the new gNB-DU A 610A within the new shared gNB-DU A / B 608) sends an initial uplink RRC message to a (wrong) new gNB-CU A 612A, which is a gNB-CU that is part of the logical new gNB A 600 associated with PLMN A , over the FI interface between the new gNB-DU A 610A and the new gNB-CU A 612A. The initial uplink RRC message includes new information (referred to herein as "shared new cell information") that provides information regarding which cell IDs are broadcast for other shared RANs. In other words, the initial uplink RRC message includes "shared new cell information", which is information regarding other cells for other PLMNs that share the same physical resources (i.e., information regarding cells for other shared RANs). This shared new cell information includes, in this example, the NG CGIs and/or PLMN IDs of the other cells that share the same physical resources. This shared new cell information is desirable in order to enable a (correct) new gNB-CU B 612B (see step 10 discussed below) to behave as if it had received the initial uplink RRC message in step 2 with NR CGIB from the new shared gNB- DUA/B 608. As illustrated, the initial uplink RRC message also includes, in this example, the C-RNTI of the UE 620 in the source cell and an RRC container comprising at least a portion of (but potentially all of) the

RRCReestabHshmentRequest fro m step 1.

• Step 3: The (wrong) new gNB-CU A 612A sends a request to a (wrong) old gNB- CUA 618A for a UE context of the UE 620. This request includes information that identifies the UE 620 (C-RNTI in this example) as well as an RRC container comprising at least a portion of (but potentially all of) the

RRCReestabHshmentRequest rom step 1 and the shared new cell information. This information included in the request is desirable to prepare for a possible redirection of the request for the UE context of the UE 620 to the correct old gNB-CU (which in this example is old gNB-CU B 618B).

• Step 4: The (wrong) old gNB-CU A 618A is unable to retrieve the UE context of the UE 620.

• Step 5: Since the old gNB-CU A 618A was unable to retrieve the UE context of the UE 620, the old gNB-CU A 618A initiates a redirection of the UE context request to the appropriate old gNB-CU (which in this example is the old gNB-CU B 618B) by sending a redirect indication message to an old shared gNB-DU A / B 614 that allocated the C-RNTI of the UE 620 in the old cell. In this example, within the old gNB-DU A / B 614, the redirect indication message is received and processed by the old gNB-DU B . This indication message of step 5 includes at least a portion of (but potentially all of) the RRCReestabHshmentRequest fro m step 1, at least a portion of (but potentially all of) the UE context request message from step 3, and the shared new cell information.

• Step 6: The old gNB-DU A / B 614 identifies the correct old gNB-CU that holds the UE context of the UE 620 associated with the C-RNTI of the UE 620 in the old cell, e.g., based on a stored mapping between the C-RNTI and the correct old gNB-CU. Again, in this example, the correct old gNB-CU is the old gNB-CU B 618B. • Step 7: The old shared gNB-DU A / B 614 sends a redirect indication message to the correct old gNB-CU B 618B. This indication message of step 7 includes at least a portion of (but potentially all of) the RRCReestabHshmentRequest fro m step 1, at least a portion of (but potentially all of) the UE context request message from step 3, and the shared new cell information.

• Step 8: The correct old gNB-CU B 618B retrieves the UE context of the UE 620 and sends a redirection indication message including the UE context to the correct new gNB-CU B 612B. In addition to the UE context, the indication message of step 8 includes at least a portion of (but potentially all of) the UE context request message from step 3, and the shared new cell information.

• Step 9: This step is only illustrated to indicate that, at this point, the redirection has ended up at the correct gNB-CU B 612B, as if the message of step 2 would have been sent to the correct gNB-CU B 612B.

• Step 10: The correct new gNB-CU B 612B sends a RRC message transfer to the new gNB-DU A / B 608. This message includes the C-RNTI of the UE 620 as a context reference. Note that indication that the UE context has been found can also be added to inform the new gNB-DU A / B 608 that a re-establishment procedure is being performed. In other words, the RRC message transfer triggers transfer of the RRC reestablishment procedure from the new gNB-DU A 610A to the new gNB-DU B 610B.

• Steps 11-13: The RRC reestablishment procedure is completed.

Importantly, while the example of Figure 5 is discussed above as being applied for network sharing, the same procedure can be used for network slicing.

[0073] Apart from network sharing and network slicing, the proposed solution for redirection in CU-DU split can be also applied to a scenario where the same operator decides to configure multiple gNB-CUs and/or multiple gNB-DUs that share the same physical resource for any other reason. The same approach is also applicable for other Radio Access Technologies (RATs) using the same or a similar architecture or functions (i.e., the embodiments described herein are not limited to 3GPP New Radio (NR)).

[0074] Although the subject matter described herein may be implemented in any appropriate type of system using any suitable components, the embodiments disclosed herein are described in relation to a wireless network, such as the example wireless network illustrated in Figure 7. For simplicity, the wireless network of Figure 7 only depicts a network 706, network nodes 760 and 760B, and Wireless Devices (WDs) 710, 710B, and 710C. In practice, a wireless network may further include any additional elements suitable to support communication between wireless devices or between a wireless device and another communication device, such as a landline telephone, a service provider, or any other network node or end device. Of the illustrated

components, the network node 760 and the WD 710 are depicted with additional detail. The wireless network may provide communication and other types of services to one or more wireless devices to facilitate the wireless devices' access to and/or use of the services provided by, or via, the wireless network.

[0075] The wireless network may comprise and/or interface with any type of communication, telecommunication, data, cellular, and/or radio network or other similar type of system. In some embodiments, the wireless network may be configured to operate according to specific standards or other types of predefined rules or

procedures. Thus, particular embodiments of the wireless network may implement communication standards, such as Global System for Mobile Communications (GSM), Universal Mobile Telecommunications System (UMTS), Long Term Evolution (LTE), and/or other suitable Second, Third, Fourth, or Fifth Generation (2G, 3G, 4G, or 5G) standards; Wireless Local Area Network (WLAN) standards, such as the IEEE 802.11 standards; and/or any other appropriate wireless communication standard, such as the Worldwide Interoperability for Microwave Access (WiMax), Bluetooth, Z-Wave, and/or ZigBee standards.

[0076] The network 706 may comprise one or more backhaul networks, core networks, Internet Protocol (IP) networks, Public Switched Telephone Networks

(PSTNs), packet data networks, optical networks, Wide Area Networks (WANs), Local Area Networks (LANs), WLANs, wired networks, wireless networks, metropolitan area networks, and other networks to enable communication between devices.

[0077] The network node 760 and the WD 710 comprise various components described in more detail below. These components work together in order to provide network node and/or wireless device functionality, such as providing wireless

connections in a wireless network. In different embodiments, the wireless network may comprise any number of wired or wireless networks, network nodes, base stations, controllers, wireless devices, relay stations, and/or any other components or systems that may facilitate or participate in the communication of data and/or signals whether via wired or wireless connections.

[0078] As used herein, network node refers to equipment capable, configured, arranged, and/or operable to communicate directly or indirectly with a wireless device and/or with other network nodes or equipment in the wireless network to enable and/or provide wireless access to the wireless device and/or to perform other functions (e.g., administration) in the wireless network. Examples of network nodes include, but are not limited to, Access Points (APs) (e.g., radio APs), Base Stations (BSs) (e.g., radio base stations, Node Bs, enhanced or evolved Node Bs (eNBs), and gNBs). Base stations may be categorized based on the amount of coverage they provide (or, stated differently, their transmit power level) and may then also be referred to as femto base stations, pico base stations, micro base stations, or macro base stations. A base station may be a relay node or a relay donor node controlling a relay. A network node may also include one or more (or all) parts of a distributed radio base station such as centralized digital units and/or Remote Radio Units (RRUs), sometimes referred to as Remote Radio Heads (RRHs). Such RRUs may or may not be integrated with an antenna as an antenna integrated radio. Parts of a distributed radio base station may also be referred to as nodes in a Distributed Antenna System (DAS). Yet further examples of network nodes include Multi-Standard Radio (MSR) equipment such as MSR BSs, network controllers such as Radio Network Controllers (RNCs) or BS Controllers (BSCs), Base Transceiver Stations (BTSs), transmission points, transmission nodes, Multi-Cell/Multicast Coordination Entities (MCEs), core network nodes (e.g., Mobile Switching Centers (MSCs), Mobility Management Entities (MMEs)), Operation and Maintenance (O&M) nodes, Operations Support System (OSS) nodes, Self-Organizing Network (SON) nodes, positioning nodes (e.g., Evolved Serving Mobile Location Center (E-SMLCs)), and/or Minimization of Drive Tests (MDTs). As another example, a network node may be a virtual network node as described in more detail below. More generally, however, network nodes may represent any suitable device (or group of devices) capable, configured, arranged, and/or operable to enable and/or provide a wireless device with access to the wireless network or to provide some service to a wireless device that has accessed the wireless network.

[0079] In Figure 7, the network node 760 includes processing circuitry 770, a device readable medium 780, an interface 790, auxiliary equipment 784, a power source 786, power circuitry 787, and an antenna 762. Although the network node 760 illustrated in the example wireless network of Figure 7 may represent a device that includes the illustrated combination of hardware components, other embodiments may comprise network nodes with different combinations of components. It is to be understood that a network node comprises any suitable combination of hardware and/or software needed to perform the tasks, features, functions, and methods disclosed herein. Moreover, while the components of the network node 760 are depicted as single boxes located within a larger box, or nested within multiple boxes, in practice, a network node may comprise multiple different physical components that make up a single illustrated component (e.g., the device readable medium 780 may comprise multiple separate hard drives as well as multiple Random Access Memory (RAM) modules).

[0080] Similarly, the network node 760 may be composed of multiple physically separate components (e.g., a Node B component and a RNC component, or a BTS component and a BSC component, etc.), which may each have their own respective components. In certain scenarios in which the network node 760 comprises multiple separate components (e.g., BTS and BSC components), one or more of the separate components may be shared among several network nodes. For example, a single RNC may control multiple Node Bs. In such a scenario, each unique Node B and RNC pair may in some instances be considered a single separate network node. In some embodiments, the network node 760 may be configured to support multiple RATs. In such embodiments, some components may be duplicated (e.g., a separate device readable medium 780 for the different RATs) and some components may be reused (e.g., the same antenna 762 may be shared by the RATs). The network node 760 may also include multiple sets of the various illustrated components for different wireless technologies integrated into the network node 760, such as, for example, GSM,

Wideband Code Division Multiple Access (WCDMA), LTE, NR, WiFi, or Bluetooth wireless technologies. These wireless technologies may be integrated into the same or a different chip or set of chips and other components within the network node 760.

[0081] The processing circuitry 770 is configured to perform any determining, calculating, or similar operations (e.g., certain obtaining operations) described herein as being provided by a network node. These operations performed by the processing circuitry 770 may include processing information obtained by the processing circuitry 770 by, for example, converting the obtained information into other information, comparing the obtained information or converted information to information stored in the network node, and/or performing one or more operations based on the obtained information or converted information, and as a result of said processing making a determination.

[0082] The processing circuitry 770 may comprise a combination of one or more of a microprocessor, a controller, a microcontroller, a Central Processing Unit (CPU), a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field

Programmable Gate Array (FPGA), or any other suitable computing device, resource, or combination of hardware, software, and/or encoded logic operable to provide, either alone or in conjunction with other network node 760 components, such as the device readable medium 780, network node 760 functionality. For example, the processing circuitry 770 may execute instructions stored in the device readable medium 780 or in memory within the processing circuitry 770. Such functionality may include providing any of the various wireless features, functions, or benefits discussed herein. In some embodiments, the processing circuitry 770 may include a System on a Chip (SOC).

[0083] In some embodiments, the processing circuitry 770 may include one or more of Radio Frequency (RF) transceiver circuitry 772 and baseband processing circuitry 774. In some embodiments, the RF transceiver circuitry 772 and the baseband processing circuitry 774 may be on separate chips (or sets of chips), boards, or units, such as radio units and digital units. In alternative embodiments, part or all of the RF transceiver circuitry 772 and the baseband processing circuitry 774 may be on the same chip or set of chips, boards, or units.

[0084] In certain embodiments, some or all of the functionality described herein as being provided by a network node, base station, eNB, or other such network device may be performed by the processing circuitry 770 executing instructions stored on the device readable medium 780 or memory within the processing circuitry 770. In alternative embodiments, some or all of the functionality may be provided by the processing circuitry 770 without executing instructions stored on a separate or discrete device readable medium, such as in a hard-wired manner. In any of those embodiments, whether executing instructions stored on a device readable storage medium or not, the processing circuitry 770 can be configured to perform the described functionality. The benefits provided by such functionality are not limited to the processing circuitry 770 alone or to other components of the network node 760, but are enjoyed by the network node 760 as a whole, and/or by end users and the wireless network generally.

[0085] The device readable medium 780 may comprise any form of volatile or non ¬ volatile computer readable memory including, without limitation, persistent storage, solid state memory, remotely mounted memory, magnetic media, optical media, RAM, Read Only Memory (ROM), mass storage media (for example, a hard disk), removable storage media (for example, a flash drive, a Compact Disk (CD) or a Digital Video Disk (DVD)), and/or any other volatile or non-volatile, non-transitory device readable and/or computer-executable memory devices that store information, data, and/or instructions that may be used by the processing circuitry 770. The device readable medium 780 may store any suitable instructions; data or information, including a computer program; software; an application including one or more of logic, rules, code, tables, etc.; and/or other instructions capable of being executed by the processing circuitry 770 and utilized by the network node 760. The device readable medium 780 may be used to store any calculations made by the processing circuitry 770 and/or any data received via the interface 790. In some embodiments, the processing circuitry 770 and the device readable medium 780 may be considered to be integrated.

[0086] The interface 790 is used in the wired or wireless communication of signaling and/or data between the network node 760, a network 706, and/or WDs 710. As illustrated, the interface 790 comprises port(s)/terminal(s) 794 to send and receive data, for example to and from the network 706 over a wired connection. The interface 790 also includes radio front end circuitry 792 that may be coupled to, or in certain embodiments a part of, the antenna 762. The radio front end circuitry 792 comprises filters 798 and amplifiers 796. The radio front end circuitry 792 may be connected to the antenna 762 and the processing circuitry 770. The radio front end circuitry 792 may be configured to condition signals communicated between the antenna 762 and the processing circuitry 770. The radio front end circuitry 792 may receive digital data that is to be sent out to other network nodes or WDs via a wireless connection. The radio front end circuitry 792 may convert the digital data into a radio signal having the appropriate channel and bandwidth parameters using a combination of the filters 798 and/or the amplifiers 796. The radio signal may then be transmitted via the antenna 762. Similarly, when receiving data, the antenna 762 may collect radio signals which are then converted into digital data by the radio front end circuitry 792. The digital data may be passed to the processing circuitry 770. In other embodiments, the interface 790 may comprise different components and/or different combinations of components.

[0087] In certain alternative embodiments, the network node 760 may not include separate radio front end circuitry 792; instead, the processing circuitry 770 may comprise radio front end circuitry and may be connected to the antenna 762 without separate radio front end circuitry 792. Similarly, in some embodiments, all or some of the RF transceiver circuitry 772 may be considered a part of the interface 790. In still other embodiments, the interface 790 may include the one or more ports or terminals 794, the radio front end circuitry 792, and the RF transceiver circuitry 772 as part of a radio unit (not shown), and the interface 790 may communicate with the baseband processing circuitry 774, which is part of a digital unit (not shown).

[0088] The antenna 762 may include one or more antennas, or antenna arrays, configured to send and/or receive wireless signals. The antenna 762 may be coupled to the radio front end circuitry 792 and may be any type of antenna capable of

transmitting and receiving data and/or signals wirelessly. In some embodiments, the antenna 762 may comprise one or more omni-directional, sector, or panel antennas operable to transmit/receive radio signals between, for example, 2 gigahertz (GFIz) and 66 GFIz. An omni-directional antenna may be used to transmit/receive radio signals in any direction, a sector antenna may be used to transmit receive radio signals from devices within a particular area, and a panel antenna may be a line of sight antenna used to transmit/receive radio signals in a relatively straight line. In some instances, the use of more than one antenna may be referred to as Multiple Input Multiple Output (MIMO). In certain embodiments, the antenna 762 may be separate from the network node 760 and may be connectable to the network node 760 through an interface or port.

[0089] The antenna 762, the interface 790, and/or the processing circuitry 770 may be configured to perform any receiving operations and/or certain obtaining operations described herein as being performed by a network node. Any information, data, and/or signals may be received from a WD, another network node, and/or any other network equipment. Similarly, the antenna 762, the interface 790, and/or the processing circuitry 770 may be configured to perform any transmitting operations described herein as being performed by a network node. Any information, data, and/or signals may be transmitted to a WD, another network node, and/or any other network equipment.

[0090] The power circuitry 787 may comprise, or be coupled to, power management circuitry and is configured to supply the components of the network node 760 with power for performing the functionality described herein. The power circuitry 787 may receive power from the power source 786. The power source 786 and/or the power circuitry 787 may be configured to provide power to the various components of the network node 760 in a form suitable for the respective components (e.g., at a voltage and current level needed for each respective component). The power source 786 may either be included in, or be external to, the power circuitry 787 and/or the network node 760. For example, the network node 760 may be connectable to an external power source (e.g., an electricity outlet) via an input circuitry or interface such as an electrical cable, whereby the external power source supplies power to the power circuitry 787. As a further example, the power source 786 may comprise a source of power in the form of a battery or battery pack which is connected to, or integrated in, the power circuitry 787. The battery may provide backup power should the external power source fail. Other types of power sources, such as photovoltaic devices, may also be used.

[0091] Alternative embodiments of the network node 760 may include additional components beyond those shown in Figure 7 that may be responsible for providing certain aspects of the network node's functionality, including any of the functionality described herein and/or any functionality necessary to support the subject matter described herein. For example, the network node 760 may include user interface equipment to allow input of information into the network node 760 and to allow output of information from the network node 760. This may allow a user to perform

diagnostic, maintenance, repair, and other administrative functions for the network node 760.

[0092] As used herein, WD refers to a device capable, configured, arranged, and/or operable to communicate wirelessly with network nodes and/or other WDs. Unless otherwise noted, the term WD may be used interchangeably herein with UE.

Communicating wirelessly may involve transmitting and/or receiving wireless signals using electromagnetic waves, radio waves, infrared waves, and/or other types of signals suitable for conveying information through air. In some embodiments, a WD may be configured to transmit and/or receive information without direct human interaction. For instance, a WD may be designed to transmit information to a network on a

predetermined schedule, when triggered by an internal or external event, or in response to requests from the network. Examples of a WD include, but are not limited to, a smart phone, a mobile phone, a cell phone, a Voice over IP (VoIP) phone, a wireless local loop phone, a desktop computer, a Personal Digital Assistant (PDA), a wireless camera, a gaming console or device, a music storage device, a playback appliance, a wearable terminal device, a wireless endpoint, a mobile station, a tablet, a laptop, Laptop Embedded Equipment (LEE), Laptop Mounted Equipment (LME), a smart device, a wireless Customer Premise Equipment (CPE), a vehicle mounted wireless terminal device, etc.. A WD may support Device-to-Device (D2D) communication, for example by implementing a 3GPP standard for sidelink communication, Vehicle-to-Vehicle (V2V), Vehicle-to-Infrastructure (V2I), Vehicle-to-Everything (V2X), and may in this case be referred to as a D2D communication device. As yet another specific example, in an Internet of Things (IoT) scenario, a WD may represent a machine or other device that performs monitoring and/or measurements, and transmits the results of such

monitoring and/or measurements to another WD and/or a network node. The WD may in this case be a Machine-to-Machine (M2M) device, which may in a 3GPP context be referred to as a Machine-Type Communication (MTC) device. As one particular example, the WD may be a UE implementing the 3GPP Narrowband IoT (NB-IoT) standard. Particular examples of such machines or devices are sensors, metering devices such as power meters, industrial machinery, home or personal appliances (e.g., refrigerators, televisions, etc.), or personal wearables (e.g., watches, fitness trackers, etc.). In other scenarios, a WD may represent a vehicle or other equipment that is capable of monitoring and/or reporting on its operational status or other functions associated with its operation. A WD as described above may represent the endpoint of a wireless connection, in which case the device may be referred to as a wireless terminal. Furthermore, a WD as described above may be mobile, in which case it may also be referred to as a mobile device or a mobile terminal.

[0093] As illustrated in Figure 7, a WD 710 includes an antenna 711, an interface 714, processing circuitry 720, a device readable medium 730, user interface equipment 732, auxiliary equipment 734, a power source 736, and power circuitry 737. The WD 710 may include multiple sets of one or more of the illustrated components for different wireless technologies supported by the WD 710, such as, for example, GSM, WCDMA, LTE, NR, WiFi, WiMAX, or Bluetooth wireless technologies, just to mention a few. These wireless technologies may be integrated into the same or different chips or set of chips as other components within the WD 710.

[0094] The antenna 711 may include one or more antennas or antenna arrays configured to send and/or receive wireless signals and is connected to the interface 714. In certain alternative embodiments, the antenna 711 may be separate from the WD 710 and be connectable to the WD 710 through an interface or port. The antenna 711, the interface 714, and/or the processing circuitry 720 may be configured to perform any receiving or transmitting operations described herein as being performed by a WD. Any information, data, and/or signals may be received from a network node and/or another WD. In some embodiments, radio front end circuitry and/or the antenna 711 may be considered an interface.

[0095] As illustrated, the interface 714 comprises radio front end circuitry 712 and the antenna 711. The radio front end circuitry 712 comprises one or more filters 718 and amplifiers 716. The radio front end circuitry 712 is connected to the antenna 711 and the processing circuitry 720 and is configured to condition signals communicated between the antenna 711 and the processing circuitry 720. The radio front end circuitry 712 may be coupled to or be a part of the antenna 711. In some embodiments, the WD 710 may not include separate radio front end circuitry 712; rather, the processing circuitry 720 may comprise radio front end circuitry and may be connected to the antenna 711. Similarly, in some embodiments, some or all of RF transceiver circuitry 722 may be considered a part of the interface 714. The radio front end circuitry 712 may receive digital data that is to be sent out to other network nodes or WDs via a wireless connection. The radio front end circuitry 712 may convert the digital data into a radio signal having the appropriate channel and bandwidth parameters using a combination of the filters 718 and/or the amplifiers 716. The radio signal may then be transmitted via the antenna 711. Similarly, when receiving data, the antenna 711 may collect radio signals which are then converted into digital data by the radio front end circuitry 712. The digital data may be passed to the processing circuitry 720. In other embodiments, the interface 714 may comprise different components and/or different combinations of components. [0096] The processing circuitry 720 may comprise a combination of one or more of a microprocessor, a controller, a microcontroller, a CPU, a DSP, an ASIC, a FPGA, or any other suitable computing device, resource, or combination of hardware, software, and/or encoded logic operable to provide, either alone or in conjunction with other WD 710 components, such as the device readable medium 730, WD 710 functionality. Such functionality may include providing any of the various wireless features or benefits discussed herein. For example, the processing circuitry 720 may execute instructions stored in the device readable medium 730 or in memory within the processing circuitry 720 to provide the functionality disclosed herein.

[0097] As illustrated, the processing circuitry 720 includes one or more of the RF transceiver circuitry 722, baseband processing circuitry 724, and application processing circuitry 726. In other embodiments, the processing circuitry 720 may comprise different components and/or different combinations of components. In certain embodiments, the processing circuitry 720 of the WD 710 may comprise a SOC. In some embodiments, the RF transceiver circuitry 722, the baseband processing circuitry 724, and the application processing circuitry 726 may be on separate chips or sets of chips. In alternative embodiments, part or all of the baseband processing circuitry 724 and the application processing circuitry 726 may be combined into one chip or set of chips, and the RF transceiver circuitry 722 may be on a separate chip or set of chips. In still alternative embodiments, part or all of the RF transceiver circuitry 722 and the baseband processing circuitry 724 may be on the same chip or set of chips, and the application processing circuitry 726 may be on a separate chip or set of chips. In yet other alternative embodiments, part or all of the RF transceiver circuitry 722, the baseband processing circuitry 724, and the application processing circuitry 726 may be combined in the same chip or set of chips. In some embodiments, the RF transceiver circuitry 722 may be a part of the interface 714. The RF transceiver circuitry 722 may condition RF signals for the processing circuitry 720.

[0098] In certain embodiments, some or all of the functionality described herein as being performed by a WD may be provided by the processing circuitry 720 executing instructions stored on the device readable medium 730, which in certain embodiments may be a computer-readable storage medium. In alternative embodiments, some or all of the functionality may be provided by the processing circuitry 720 without executing instructions stored on a separate or discrete device readable storage medium, such as in a hard-wired manner. In any of those particular embodiments, whether executing instructions stored on a device readable storage medium or not, the processing circuitry 720 can be configured to perform the described functionality. The benefits provided by such functionality are not limited to the processing circuitry 720 alone or to other components of the WD 710, but are enjoyed by the WD 710 as a whole, and/or by end users and the wireless network generally.

[0099] The processing circuitry 720 may be configured to perform any determining, calculating, or similar operations (e.g., certain obtaining operations) described herein as being performed by a WD. These operations, as performed by the processing circuitry 720, may include processing information obtained by the processing circuitry 720 by, for example, converting the obtained information into other information, comparing the obtained information or converted information to information stored by the WD 710, and/or performing one or more operations based on the obtained information or converted information, and as a result of said processing making a determination.

[0100] The device readable medium 730 may be operable to store a computer program; software; an application including one or more of logic, rules, code, tables, etc.; and/or other instructions capable of being executed by the processing circuitry 720. The device readable medium 730 may include computer memory (e.g., RAM or ROM), mass storage media (e.g., a hard disk), removable storage media (e.g., a CD or a DVD), and/or any other volatile or non-volatile, non-transitory device readable and/or computer executable memory devices that store information, data, and/or instructions that may be used by the processing circuitry 720. In some embodiments, the

processing circuitry 720 and the device readable medium 730 may be considered to be integrated.

[0101] The user interface equipment 732 may provide components that allow for a human user to interact with the WD 710. Such interaction may be of many forms, such as visual, audial, tactile, etc. The user interface equipment 732 may be operable to produce output to the user and to allow the user to provide input to the WD 710. The type of interaction may vary depending on the type of user interface equipment 732 installed in the WD 710. For example, if the WD 710 is a smart phone, the interaction may be via a touch screen; if the WD 710 is a smart meter, the interaction may be through a screen that provides usage (e.g., the number of gallons used) or a speaker that provides an audible alert (e.g., if smoke is detected). The user interface equipment 732 may include input interfaces, devices and circuits, and output interfaces, devices and circuits. The user interface equipment 732 is configured to allow input of information into the WD 710, and is connected to the processing circuitry 720 to allow the processing circuitry 720 to process the input information. The user interface equipment 732 may include, for example, a microphone, a proximity or other sensor, keys/buttons, a touch display, one or more cameras, a Universal Serial Bus (USB) port, or other input circuitry. The user interface equipment 732 is also configured to allow output of information from the WD 710 and to allow the processing circuitry 720 to output information from the WD 710. The user interface equipment 732 may include, for example, a speaker, a display, vibrating circuitry, a USB port, a headphone interface, or other output circuitry. Using one or more input and output interfaces, devices, and circuits of the user interface equipment 732, the WD 710 may communicate with end users and/or the wireless network, and allow them to benefit from the functionality described herein.

[0102] The auxiliary equipment 734 is operable to provide more specific functionality which may not be generally performed by WDs. This may comprise specialized sensors for doing measurements for various purposes, interfaces for additional types of communication such as wired communications, etc. The inclusion and type of components of the auxiliary equipment 734 may vary depending on the embodiment and/or scenario.

[0103] The power source 736 may, in some embodiments, be in the form of a battery or battery pack. Other types of power sources, such as an external power source (e.g., an electricity outlet), photovoltaic devices, or power cells may also be used. The WD 710 may further comprise the power circuitry 737 for delivering power from the power source 736 to the various parts of the WD 710 which need power from the power source 736 to carry out any functionality described or indicated herein. The power circuitry 737 may in certain embodiments comprise power management circuitry. The power circuitry 737 may additionally or alternatively be operable to receive power from an external power source, in which case the WD 710 may be connectable to the external power source (such as an electricity outlet) via input circuitry or an interface such as an electrical power cable. The power circuitry 737 may also in certain embodiments be operable to deliver power from an external power source to the power source 736. This may be, for example, for the charging of the power source 736. The power circuitry 737 may perform any formatting, converting, or other modification to the power from the power source 736 to make the power suitable for the respective components of the WD 710 to which power is supplied.

[0104] Figure 8 illustrates one embodiment of a UE in accordance with various aspects described herein. As used herein, a user equipment or UE may not necessarily have a user in the sense of a human user who owns and/or operates the relevant device. Instead, a UE may represent a device that is intended for sale to, or operation by, a human user but which may not, or which may not initially, be associated with a specific human user (e.g., a smart sprinkler controller). Alternatively, a UE may represent a device that is not intended for sale to, or operation by, an end user but which may be associated with or operated for the benefit of a user (e.g., a smart power meter). A UE 800 may be any UE identified by 3GPP, including a NB-IoT UE, a MTC UE, and/or an enhanced MTC (eMTC) UE. The UE 800, as illustrated in Figure 8, is one example of a WD configured for communication in accordance with one or more communication standards promulgated by 3GPP, such as 3GPP's GSM, UMTS, LTE, and/or 5G standards. As mentioned previously, the term WD and UE may be used interchangeable. Accordingly, although Figure 8 is a UE, the components discussed herein are equally applicable to a WD, and vice-versa.

[0105] In Figure 8, the UE 800 includes processing circuitry 801 that is operatively coupled to an input/output interface 805, an RF interface 809, a network connection interface 811, memory 815 including RAM 817, ROM 819, and a storage medium 821 or the like, a communication subsystem 831, a power source 813, and/or any other component, or any combination thereof. The storage medium 821 includes an operating system 823, an application program 825, and data 827. In other

embodiments, the storage medium 821 may include other similar types of information. Certain UEs may utilize all of the components shown in Figure 8, or only a subset of the components. The level of integration between the components may vary from one UE to another UE. Further, certain UEs may contain multiple instances of a component, such as multiple processors, memories, transceivers, transmitters, receivers, etc.

[0106] In Figure 8, the processing circuitry 801 may be configured to process computer instructions and data. The processing circuitry 801 may be configured to implement any sequential state machine operative to execute machine instructions stored as machine-readable computer programs in the memory, such as one or more hardware-implemented state machines (e.g., in discrete logic, FPGA, ASIC, etc.);

programmable logic together with appropriate firmware; one or more stored programs, general purpose processors, such as a microprocessor or DSP, together with appropriate software; or any combination of the above. For example, the processing circuitry 801 may include two CPUs. Data may be information in a form suitable for use by a computer.

[0107] In the depicted embodiment, the input/output interface 805 may be configured to provide a communication interface to an input device, output device, or input and output device. The UE 800 may be configured to use an output device via the input/output interface 805. An output device may use the same type of interface port as an input device. For example, a USB port may be used to provide input to and output from the UE 800. The output device may be a speaker, a sound card, a video card, a display, a monitor, a printer, an actuator, an emitter, a smartcard, another output device, or any combination thereof. The UE 800 may be configured to use an input device via the input/output interface 805 to allow a user to capture information into the UE 800. The input device may include a touch-sensitive or presence-sensitive display, a camera (e.g., a digital camera, a digital video camera, a web camera, etc.), a microphone, a sensor, a mouse, a trackball, a directional pad, a trackpad, a scroll wheel, a smartcard, and the like. The presence-sensitive display may include a capacitive or resistive touch sensor to sense input from a user. A sensor may be, for instance, an accelerometer, a gyroscope, a tilt sensor, a force sensor, a magnetometer, an optical sensor, a proximity sensor, another like sensor, or any combination thereof. For example, the input device may be an accelerometer, a magnetometer, a digital camera, a microphone, and an optical sensor.

[0108] In Figure 8, the RF interface 809 may be configured to provide a

communication interface to RF components such as a transmitter, a receiver, and an antenna. The network connection interface 811 may be configured to provide a communication interface to a network 843A. The network 843A may encompass wired and/or wireless networks such as a LAN, a WAN, a computer network, a wireless network, a telecommunications network, another like network or any combination thereof. For example, the network 843A may comprise a WiFi network. The network connection interface 811 may be configured to include a receiver and a transmitter interface used to communicate with one or more other devices over a communication network according to one or more communication protocols, such as Ethernet,

Transmission Control Protocol (TCP) / IP, Synchronous Optical Networking (SONET), Asynchronous Transfer Mode (ATM), or the like. The network connection interface 811 may implement receiver and transmitter functionality appropriate to the communication network links (e.g., optical, electrical, and the like). The transmitter and receiver functions may share circuit components, software, or firmware, or alternatively may be implemented separately.

[0109] The RAM 817 may be configured to interface via a bus 802 to the processing circuitry 801 to provide storage or caching of data or computer instructions during the execution of software programs such as the operating system, application programs, and device drivers. The ROM 819 may be configured to provide computer instructions or data to the processing circuitry 801. For example, the ROM 819 may be configured to store invariant low-level system code or data for basic system functions such as basic Input and Output (I/O), startup, or reception of keystrokes from a keyboard that are stored in a non-volatile memory. The Storage medium 821 may be configured to include memory such as RAM, ROM, Programmable ROM (PROM), Erasable PROM (EPROM), Electrically EPROM (EEPROM), magnetic disks, optical disks, floppy disks, hard disks, removable cartridges, or flash drives. In one example, the storage medium 821 may be configured to include the operating system 823, the application program 825 such as a web browser application, a widget or gadget engine, or another application, and the data file 827. The storage medium 821 may store, for use by the UE 800, any of a variety of various operating systems or combinations of operating systems.

[0110] The storage medium 821 may be configured to include a number of physical drive units, such as a Redundant Array of Independent Disks (RAID), a floppy disk drive, flash memory, a USB flash drive, an external hard disk drive, a thumb drive, a pen drive, a key drive, a High-Density Digital Versatile Disc (HD-DVD) optical disc drive, an internal hard disk drive, a Blu-Ray optical disc drive, a Holographic Digital Data Storage (HDDS) optical disc drive, an external mini-Dual In-Line Memory Module (DIMM), Synchronous Dynamic RAM (SDRAM), external micro-DIMM SDRAM, smartcard memory such as a Subscriber Identity Module (SIM) or a Removable User Identity (RUIM) module, other memory, or any combination thereof. The storage medium 821 may allow the UE 800 to access computer-executable instructions, application programs, or the like, stored on transitory or non-transitory memory media, to off-load data or to upload data. An article of manufacture, such as one utilizing a communication system, may be tangibly embodied in the storage medium 821, which may comprise a device readable medium.

[0111] In Figure 8, the processing circuitry 801 may be configured to communicate with a network 843B using the communication subsystem 831. The network 843A and the network 843B may be the same network or networks or different network or networks. The communication subsystem 831 may be configured to include one or more transceivers used to communicate with the network 843B. For example, the communication subsystem 831 may be configured to include one or more transceivers used to communicate with one or more remote transceivers of another device capable of wireless communication such as another WD, UE, or base station of a RAN according to one or more communication protocols, such as IEEE 802.7, Code Division Multiple Access (CDMA), WCDMA, GSM, LTE, Universal Terrestrial RAN (UTRAN), WiMax, or the like. Each transceiver may include a transmitter 833 and/or a receiver 835 to implement transmitter or receiver functionality, respectively, appropriate to the RAN links (e.g., frequency allocations and the like). Further, the transmitter 833 and the receiver 835 of each transceiver may share circuit components, software, or firmware, or alternatively may be implemented separately.

[0112] In the illustrated embodiment, the communication functions of the

communication subsystem 831 may include data communication, voice communication, multimedia communication, short-range communications such as Bluetooth, near-field communication, location-based communication such as the use of the Global Positioning System (GPS) to determine a location, another like communication function, or any combination thereof. For example, the communication subsystem 831 may include cellular communication, WiFi communication, Bluetooth communication, and GPS communication. The network 843B may encompass wired and/or wireless networks such as a LAN, a WAN, a computer network, a wireless network, a telecommunications network, another like network, or any combination thereof. For example, the network 843B may be a cellular network, a WiFi network, and/or a near-field network. A power source 813 may be configured to provide Alternating Current (AC) or Direct Current (DC) power to components of the UE 800.

[0113] The features, benefits, and/or functions described herein may be

implemented in one of the components of the UE 800 or partitioned across multiple components of the UE 800. Further, the features, benefits, and/or functions described herein may be implemented in any combination of hardware, software, or firmware. In one example, the communication subsystem 831 may be configured to include any of the components described herein. Further, the processing circuitry 801 may be configured to communicate with any of such components over the bus 802. In another example, any of such components may be represented by program instructions stored in memory that, when executed by the processing circuitry 801, perform the

corresponding functions described herein. In another example, the functionality of any of such components may be partitioned between the processing circuitry 801 and the communication subsystem 831. In another example, the non-computationally intensive functions of any of such components may be implemented in software or firmware and the computationally intensive functions may be implemented in hardware.

[0114] Figure 9 is a schematic block diagram illustrating a virtualization environment 900 in which functions implemented by some embodiments may be virtualized. In the present context, virtualizing means creating virtual versions of apparatuses or devices which may include virtualizing hardware platforms, storage devices, and networking resources. As used herein, virtualization can be applied to a node (e.g., a virtualized base station or a virtualized radio access node) or to a device (e.g., a UE, a WD, or any other type of communication device) or components thereof and relates to an implementation in which at least a portion of the functionality is implemented as one or more virtual components (e.g., via one or more applications, components, functions, virtual machines, or containers executing on one or more physical processing nodes in one or more networks).

[0115] In some embodiments, some or all of the functions described herein may be implemented as virtual components executed by one or more virtual machines implemented in one or more virtual environments 900 hosted by one or more of hardware nodes 930. Further, in embodiments in which the virtual node is not a radio access node or does not require radio connectivity (e.g., a core network node), then the network node may be entirely virtualized.

[0116] The functions may be implemented by one or more applications 920 (which may alternatively be called software instances, virtual appliances, network functions, virtual nodes, virtual network functions, etc.) operative to implement some of the features, functions, and/or benefits of some of the embodiments disclosed herein. The applications 920 are run in the virtualization environment 900 which provides hardware 930 comprising processing circuitry 960 and memory 990. The memory 990 contains instructions 995 executable by the processing circuitry 960 whereby the application 920 is operative to provide one or more of the features, benefits, and/or functions disclosed herein.

[0117] The virtualization environment 900 comprises general-purpose or special- purpose network hardware devices 930 comprising a set of one or more processors or processing circuitry 960, which may be Commercial Off-the-Shelf (COTS) processors, dedicated ASICs, or any other type of processing circuitry including digital or analog hardware components or special purpose processors. Each hardware device 930 may comprise memory 990-1 which may be non-persistent memory for temporarily storing instructions 995 or software executed by the processing circuitry 960. Each hardware device 930 may comprise one or more Network Interface Controllers (NICs) 970, also known as network interface cards, which include a physical network interface 980. Each hardware device 930 may also include non-transitory, persistent, machine-readable storage media 990-2 having stored therein software 995 and/or instructions executable by the processing circuitry 960. The software 995 may include any type of software including software for instantiating one or more virtualization layers 950 (also referred to as hypervisors), software to execute virtual machines 940, as well as software allowing it to execute functions, features, and/or benefits described in relation with some embodiments described herein.

[0118] The virtual machines 940, comprise virtual processing, virtual memory, virtual networking or interface, and virtual storage, and may be run by a corresponding virtualization layer 950 or hypervisor. Different embodiments of the instance of virtual appliance 920 may be implemented on one or more of the virtual machines 940, and the implementations may be made in different ways.

[0119] During operation, the processing circuitry 960 executes the software 995 to instantiate the hypervisor or virtualization layer 950, which may sometimes be referred to as a Virtual Machine Monitor (VMM). The virtualization layer 950 may present a virtual operating platform that appears like networking hardware to the virtual machine 940.

[0120] As shown in Figure 9, the hardware 930 may be a standalone network node with generic or specific components. The hardware 930 may comprise an antenna 9225 and may implement some functions via virtualization. Alternatively, the hardware 930 may be part of a larger cluster of hardware (e.g., such as in a data center or CPE) where many hardware nodes work together and are managed via a Management and Orchestration (MANO) 9100, which, among others, oversees lifecycle management of the applications 920.

[0121] Virtualization of the hardware is in some contexts referred to as Network Function Virtualization (NFV). NFV may be used to consolidate many network equipment types onto industry standard high volume server hardware, physical switches, and physical storage, which can be located in data centers and CPE.

[0122] In the context of NFV, the virtual machine 940 may be a software

implementation of a physical machine that runs programs as if they were executing on a physical, non-virtualized machine. Each of the virtual machines 940, and that part of the hardware 930 that executes that virtual machine 940, be it hardware dedicated to that virtual machine 940 and/or hardware shared by that virtual machine 940 with others of the virtual machines 940, forms a separate Virtual Network Element (VNE).

[0123] Still in the context of NFV, Virtual Network Function (VNF) is responsible for handling specific network functions that run in one or more virtual machines 940 on top of the hardware networking infrastructure 930 and corresponds to the application 920 in Figure 9.

[0124] In some embodiments, one or more radio units 9200 that each include one or more transmitters 9220 and one or more receivers 9210 may be coupled to the one or more antennas 9225. The radio units 9200 may communicate directly with the hardware nodes 930 via one or more appropriate network interfaces and may be used in combination with the virtual components to provide a virtual node with radio capabilities, such as a radio access node or a base station.

[0125] In some embodiments, some signaling can be effected with the use of a control system 9230, which may alternatively be used for communication between the hardware nodes 930 and the radio unit 9200.

[0126] Any appropriate steps, methods, features, functions, or benefits disclosed herein may be performed through one or more functional units or modules of one or more virtual apparatuses. Each virtual apparatus may comprise a number of these functional units. These functional units may be implemented via processing circuitry, which may include one or more microprocessor or microcontrollers, as well as other digital hardware, which may include DSPs, special-purpose digital logic, and the like.

The processing circuitry may be configured to execute program code stored in memory, which may include one or several types of memory such as ROM, RAM, cache memory, flash memory devices, optical storage devices, etc. Program code stored in memory includes program instructions for executing one or more telecommunications and/or data communications protocols as well as instructions for carrying out one or more of the techniques described herein. In some implementations, the processing circuitry may be used to cause the respective functional unit to perform corresponding functions according one or more embodiments of the present disclosure.

[0127] The term unit may have conventional meaning in the field of electronics, electrical devices, and/or electronic devices and may include, for example, electrical and/or electronic circuitry, devices, modules, processors, memories, logic solid state and/or discrete devices, computer programs or instructions for carrying out respective tasks, procedures, computations, outputs, and/or displaying functions, and so on, as such as those that are described herein.

[0128] Some example embodiments of the present disclosure are as follows.

[0129] Embodiment 1 : A method performed by a first distributed unit (gNB-DU A / E s) of a first base station (gNB A ) associated with a first PLMN (PLMN A ) or a first network slice (Slice A ) wherein the first base station (gNB A ) shares physical layer and/or MAC layer resources with a second base station (gNB fi ) associated with a second PLMN (PLMNB) or a second network slice (Slice B ), the method comprising: receiving (Fig. 5, step 1), from a UE, a connection reestablishment request comprising an identity of the UE in a source cell to which the UE was connected prior to sending the connection reestablishment request and an identity of the source cell; and sending (Fig. 5, step 2) an initial message to a first central unit (new gNB-CU A ) of the first base station (gNB A ), the initial message comprising information regarding a second cell served by the second base station (gNB e ) using the shared physical layer and/or MAC layer resources.

[0130] Embodiment 2: The method of embodiment 1 wherein the connection reestablishment request is a RRC Reestablishment Request.

[0131] Embodiment 3: The method of embodiment 2 wherein the information regarding the second cell served by the second base station (gNB e ) using the shared physical layer and/or MAC layer resources comprises a Cell Group Identifier, CGI, of the second cell and/or a PLMN ID of the second PLMN (PLMNB) associated with the second cell.

[0132] Embodiment 4: A method performed by a first central unit (old gNB-CU A ) of a first base station (gNB A ) associated with a first PLMN (PLMN A ) or a first network slice (Slice A ) for a connection reestablishment procedure for a UE, wherein the first base station (gNB A ) shares physical layer and/or MAC layer resources with a second base station ¾NBB) associated with a second PLMN (PLMNB) or a second network slice (Slices), the method comprising: receiving (Fig. 5, step 3), from a second central unit (new gNB-CU A ), a request to retrieve a UE context of the UE, the request comprising an identity of the UE in a source cell to which the UE was connected prior to connection reestablishment; determining (Fig. 5, step 4) that the UE context of the UE cannot be found by the first central unit (old gNB-CU A ) of the first base station (gNB A ); and upon determining that the UE context of the UE cannot be found, sending (Fig. 5, step 5) a message to a distributed unit (old gNB-DU A / B ) that allocated the identity of the UE in the source cell to initiate redirection of the request to retrieve the UE context of the UE to a correct central unit.

[0133] Embodiment 5: The method of embodiment 4 wherein the request to retrieve the UE context of the UE further comprises: at least a portion of a connection

reestablishment request message sent by the UE to initiate the connection

reestablishment procedure; and/or shared cell information.

[0134] Embodiment 6: The method of embodiment 4 or 5 wherein the message sent to the distributed unit (old gNB-DU A / B ) comprises: the identity of the UE in the source cell; at least a portion of a connection reestablishment request message sent by the UE to initiate the connection reestablishment procedure; at least a portion of the request to retrieve the UE context of the UE; and/or shared cell information.

[0135] Embodiment 7: The method of embodiment 5 or 6 wherein the shared cell information comprises a Cell Group Identifier, CGI, of another cell and/or a PLMN ID of the second PLMN associated with the other cell.

[0136] Embodiment 8: A method performed by a first distributed unit (old gNB- DU A / B ) of a first base station (gNB e ) associated with a first PLMN (PLMNB) or a first network slice (Slice B ) for a connection reestablishment procedure for a UE, wherein the first base station (gNB e ) shares physical layer and/or MAC layer resources with a second base station (gNB A ) associated with a second PLMN (PLMN A ) or a second network slice (SliceA), the method comprising: receiving (Fig. 5, step 5), from a central unit (old gNB- CU A ) of the second base station (gNB A ), a message to initiate redirection of a request to retrieve a UE context of the UE to a correct central unit, the message comprising an identity of the UE in a source cell to which the UE was connected prior to connection reestablishment; identifying (Fig. 5, step 6) a correct central unit (old gNB-CU E s) of the first base station (gNB B ) from which to retrieve the UE context of the UE based on the identity of the UE in the source cell; and sending (Fig. 5, step 7), to the correct central unit (old gNB-CU B ) of the first base station (gNB B ), a message that redirects the request to retrieve the UE context of the UE to the correct central unit (old gNB-CU B ) of the first base station (gNB B ).

[0137] Embodiment 9: A method performed by a first central unit (old gNB-CU B ) of a first base station (gNB B ) associated with a first PLMN (PLMN B ) or a first network slice (Slice B ) for a connection reestablishment procedure for a UE, wherein the first base station (gNB B ) shares physical layer and/or MAC layer resources with a second base station (gNB A ) associated with a second PLMN (PLMN A ) or a second network slice (Slice A ), the method comprising: receiving (Fig. 5, step 7), from a distributed unit (old gNB-DU A / B ) of the first base station (gNB B ), a message that redirects a request to retrieve a UE context of the UE to the first central unit (old gNB-CU B ) of the first base station (gNB B ); upon receiving the message, retrieving the UE context of the UE; and sending (Fig. 5, step 8) the UE context of the UE to a central unit (new gNB-CU B ) associated with a correct distributed unit (new gNB-DU A / B ) for connection

reestablishment for the UE.

[0138] Embodiment 10: A method performed by a distributed unit (new gNB-DU A / B ) of a first base station (gNB B ) associated with a first PLMN (PLMN B ) or a first network slice (Slice B ) for a connection reestablishment procedure for a UE, wherein the first base station (gNB B ) shares physical layer and/or MAC layer resources with a second base station (gNB A ) associated with a second PLMN (PLMN A ) or a second network slice (Slice A ), the method comprising: receiving (Fig. 5, step 10), from a central unit (new gNB-CU B ) of the first base station (gNB B ), a message that transfers the connection reestablishment procedure for the UE to the distributed unit (new gNB-DU A / B ) of the first base station (gNB B ); and completing (Fig. 5, steps 11-13) the connection

reestablishment procedure. [0139] Embodiment 11: A node implementing a central unit or a distributed unit of a base station, the node comprising: a network interface; and processing circuitry associated with the network interface, the processing circuitry configured to cause the node to perform the method of any one of embodiments 1 to 10.

[0140] At least some of the following abbreviations may be used in this disclosure. If there is an inconsistency between abbreviations, preference should be given to how it is used above. If listed multiple times below, the first listing should be preferred over any subsequent listing(s).

• 2G Second Generation

• 3G Third Generation

• 3GPP Third Generation Partnership Project

• 4G Fourth Generation

• 5G Fifth Generation

• 5GC Fifth Generation Core Network

• 5GS Fifth Generation System

• AC Alternating Current

• AMF Access and Mobility Management Function

• AP Access Point

• ASIC Application Specific Integrated Circuit

• ATM Asynchronous Transfer Mode

• BS Base Station

• BSC Base Station Controller

• BTS Base Transceiver Station

• CD Compact Disk

• CDMA Code Division Multiple Access

• CGI Cell Global Identity

• COTS Commercial Off-the-Shelf

• CP Control Plane

• CPE Customer Premise Equipment

• CPU Central Processing Unit

• C-RNTI Cell Radio Network Temporary Identifier

• CU Centralized Unit

• D2D Device-to-Device • DAS Distributed Antenna System

• DC Direct Current

• DIMM Dual In-Line Memory Module

• DSP Digital Signal Processor

• DU Distributed Unit

• DVD Digital Video Disk

• EEPROM Electrically Erasable Programmable Read Only Memory

• eMTC Enhanced Machine Type Communication

• eNB Enhanced or Evolved Node B

• EN-DC Evolved Universal Terrestrial Radio Access Network New

Radio - Dual Connectivity

• EPROM Erasable Programmable Read Only Memory

• E-SMLC Evolved Serving Mobile Location Center

• E-UTRAN Evolved Universal Terrestrial Radio Access Network

• FDD Frequency Division Duplex

• FPGA Field Programmable Gate Array

• GFIz Gigahertz

• gNB Next Generation Node B

• gNB-CU Next Generation Node B Central Unit

• gNB-DU Next Generation Node B Distributed Unit

• GPS Global Positioning System

• GSM Global System for Mobile Communications

• HDDS Holographic Digital Data Storage

• HD-DVD High-Density Digital Versatile Disc

• HW Hardware

• ID Identity

• I/O Input and Output

• IoT Internet of Things

• IP Internet Protocol

• LAN Local Area Network

• LEE Laptop Embedded Equipment

• LME Laptop Mounted Equipment

• LTE Long Term Evolution • M2M Machine-to-Machine

• MAC Medium Access Control

• MAC-I Message Authentication Code for Integrity

• MANO Management and Orchestration

• MCE Multi-Cell/Multicast Coordination Entity

• MDT Minimization of Drive Tests

• MIMO Multiple Input Multiple Output

• MME Mobility Management Entity

• MOCN Multi Operator Core Network

• MSC Mobile Switching Center

• MSR Multi-Standard Radio

• MTC Machine Type Communication

• NB-IoT Narrowband Internet of Things

• NFV Network Function Virtualization

• NG Next Generation

• NGMN Next Generation Mobile Network

• NIC Network Interface Controller

• NR New Radio

• O&M Operation and Maintenance

• OSS Operations Support System

• PCI Physical Cell Identity

• PDA Personal Digital Assistant

• PHY Physical

• PLMN Public Land Mobile Network

• PROM Programmable Read Only Memory

• PSTN Public Switched Telephone Networks

• RAID Redundant Array of Independent Disks

• RAM Random Access Memory

• RAN Radio Access Network

• RAT Radio Access Technology

• RF Radio Frequency

• RNC Radio Network Controller

• RNL Radio Network Layer • ROM Read Only Memory

• RRC Radio Resource Control

• RRH Remote Radio Head

• RRU Remote Radio Unit

• RUIM Removable User Identity

• SDRAM Synchronous Dynamic Random Access Memory

• SIM Subscriber Identity Module

• S-NSSAI Single Network Slice Selection Assistance Information

• SOC System on a Chip

• SON Self-Organizing Network

• SONET Synchronous Optical Networking

• SW Software

• TA Tracking Area

• TAC Tracking Area Code

• TAI Tracking Area Identity

• TCP Transmission Control Protocol

• TDD Time Division Duplex

• TNL Transport Network Layer

• TS Technical Specification

• UE User Equipment

• UMTS Universal Mobile Telecommunications System

• UP User Plane

• USB Universal Serial Bus

• UTRAN Universal Terrestrial Radio Access Network

• V2I Vehicle-to-Infrastructure

• V2V Vehicle-to-Vehicle

• V2X Vehicle-to-Everything

• VMM Virtual Machine Monitor

• VNE Virtual Network Element

• VNF Virtual Network Function

• VoIP Voice over Internet Protocol

• WAN Wide Area Network

• WCDMA Wideband Code Division Multiple Access • WD Wireless Device

• WiMax Worldwide Interoperability for Microwave Access

• WLAN Wireless Local Area Network

[0141] Those skilled in the art will recognize improvements and modifications to the embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein.