Field

The present disclosure relates to methods, apparatuses and computer program products for controlling broadcasting in a communication system.

Background

Data can be communicated between communication devices such as user or terminal devices, base stations/access points and/or other nodes. Communication may be provided, for example, by means of a communication network and one or more compatible communication devices. A communication device at a network side provides an access point to the system and is provided with an appropriate signal receiving and transmitting apparatus for enabling communications, for example enabling other devices to access the communication system. Communication may comprise, for example, communication of data for carrying communications such as voice, video, electronic mail (email), text message, multimedia and/or content data and so on. Non-limiting examples of services provided comprise two-way or multiway calls, data communication, multimedia services and access to a data network system, such as the Internet. It is also possible to multicast/broadcast data to communication devices.

In a mobile or wireless communication system at least a part of data communication between at least two devices occurs over a wireless or radio link. Examples of wireless systems comprise public land mobile networks (PLMN), satellite-based communication systems and different wireless local networks, for example wireless local area networks (WLAN). The wider communication system can be accessed by means of an appropriate communication device or terminal. Such a device is often referred to as user equipment (UE). A communication device is provided with an appropriate signal receiving and transmitting apparatus for enabling communications, for example enabling access to a communication network or communications directly with other users. A communication device of a user may receive signalling by a station at a radio access network, for example a base station, and transmit and/or receive communications accordingly. The communication system and associated devices typically operate in accordance with a given standard or specification which sets out what the various entities associated with the system are permitted to do and how that should be achieved. Communication protocols and/or parameters which shall be used for the connection are also typically defined. One example of a communications system is UTRAN (3G radio). Other examples of communication systems are the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radioaccess technology and so-called fifth generation (5G) or New Radio (NR) networks. 5G is being standardized by the 3rd Generation Partnership Project (3GPP).

Data can be broadcast to user devices. Broadcast refers to the ability to deliver content to multiple users in a broadcast area. An example of broadcast services is Multicast Broadcast Service (MBS) which provides a point-to-multipoint communication scheme where unlike in unicast services data can be transmitted simultaneously from a single source to multiple destinations/devices.

Summary

In accordance with an aspect there is provided a method for controlling a broadcast session by stations in a session service area, the method comprising receiving a message related to the broadcast session from a session management function, generating an updated information record regarding stations associated with the broadcast session, determining whether there is a change between the updated information record and an earlier information record regarding stations associated with the broadcast session, and sending a session control message accordingly to at least one station.

According to another aspect there is provided an apparatus comprising at least one processor and at least one memory including a computer program code, the at least one memory and computer program code configured to, with the at least one processor, cause the apparatus at least to receive a message related to the broadcast session from a session management function, generate an updated information record regarding stations associated with the broadcast session, determine whether there is a change between the updated information record and an earlier information record regarding stations associated with the broadcast session, and send a session control message accordingly to at least one station. According to a further aspect a method for controlling a broadcast session by stations in a session service area is provided, the method comprising sending from a session management function to an access and mobility management function a message related to the broadcast session, and including in the message an update indication that the message contains updated information relating to the broadcast session for controlling sending of session update messages by the access and mobility management function to at least one station.

An apparatus for a session management function comprising at least one processor and at least one memory including a computer program code may also be provided, the at least one memory and computer program code configured to, with the at least one processor, cause the apparatus at least to send to an access and mobility management function a message related to the broadcast session, and include in the message an update indication that the message contains updated information relating to the broadcast session to control sending of session update messages by the access and mobility management function to at least one station.

According to an yet further aspect there is provided apparatus for a station comprising at least one processor and at least one memory including a computer program code, the at least one memory and computer program code configured to, with the at least one processor, cause the apparatus to perform at least one of including in a session update response an indication that the station is no longer within a broadcasting area of a broadcasting session when the cells served by the station are no longer a part of the broadcast area of the session, an/or including in a session update response an indication that the station remains within the broadcasting area of the broadcasting session when there are still cells served by the station that are a part of the broadcast area of the session.

A method for the operation at the station may also be provided.

In accordance with a more specific aspect the session control message comprises one of a session release message, a session setup message or a session update message.

Generating an updated information record may comprise determining information for the updated record from the message and/or generating the earlier information record comprises determining information for the earlier information record from an earlier message from the session management function. A change in at least one cell or tracking area provided by the at least one station may be determined. A change relating to a station may be determined by identifying, in response to the message received from the session management function including a broadcast area encoded as a list of tracking areas and list of cells, that information of the cells or tracking areas of the station involved in the broadcast area has changed in comparison of the broadcast area received earlier when generating the earlier information record.

Generating an updated information record may comprise identifying, in response to the message received from the session management function including a broadcast area encoded as a list of tracking areas and list of cells, stations associated with the tracking areas, and identifying additional stations by taking the most significant bits of the received identities of the cells on the list.

Generating an updated information record may comprise determining, in response to a message received from a session management function including a list of tracking areas comprising a broadcast area, stations present in an earlier information record which can be associated with at least one tracking area of the received list of tracking areas, sending a session update message to the determined stations, receiving responses from the determined stations indicating the relevance of the responding station being in the information record, and generating the updated information record regarding stations associated with the broadcast session based on the responses.

Generating an updated information record may also comprise determining new stations associated with at least one tracking area of a received list of tracking areas that are not in an earlier information record, and sending a session setup message to the determined new stations.

Generating an updated information record may also comprise determining stations present in an earlier information record which cannot be associated with any tracking area of a received list of tracking areas, and sending a session release message to these stations.

Stations associated with a tracking area may be derived from earlier messages received from the stations, wherein the earlier messages comprise mapping information between the stations and tracking areas. It can be determined from responses from stations which of the stations in a tracking area are within a broadcasting area of a broadcasting session, and including only stations determined to be in the broadcasting area in an updated information record.

It can be determined that a station appears in an earlier information record and an updated information record. In response either a session update message is sent to the station in response to determining at least a change relating to the station, or it is refrained from sending a session update message to the station when no change is determined.

An update indicator may be sent by and received from a session management function for indicating that a message from the session management function contains updated information relating to the broadcast session. Sending of session control messages can be controlled accordingly. The indicator may comprise an indicator of a broadcast service information update and/or an indicator of a broadcast area change. The controlling may comprise determining whether a session update message shall be sent to at least one station based on the indicator. The indicator of a broadcast area change maty be provided per tracking area for each tracking area in a list of tracking areas. A session update message may be sent to a station when a change of broadcast area is indicated for at least one tracking area to which the station belongs or when a change of broadcast service information is indicated in the message received from the session management function. It can be refrained from sending a session update message to the station when no change relating to the station is determined.

An indicator of a multicast broadcast service information update and/or indicator of a broadcast area change may be used to indicate to an access and mobility management function that it is to determine whether a session update message shall be sent to at least one station.

The earlier message may comprise a session start message or a session update message. The received message may comprise a session update message.

A session management function may comprise a multicast/broadcast session management function. A station may comprise radio access network base station. Messages from the multicast/broadcast session management function may be received and the session control message to at least one station sent by an access and mobility management function.

A station can receive a session setup message including a broadcast area comprising a list of tracking areas and/or cells, and respond thereto by a session setup failure message when the station is not involved in any cell and tracking area of the broadcast area.

Means for implementing the herein disclosed operations and functions can also be provided. The means can comprise appropriately configured hardware and software.

A computer software product embodying at least a part of the herein described functions may also be provided. In accordance with an aspect a computer program comprises instructions for performing at least one of the methods described herein.

Brief description of Drawings

Some aspects will now be described in further detail, by way of example only, with reference to the following examples and accompanying drawings, in which:

Figure 1 illustrates an example of a system where the invention can be practiced;

Figure 2 shows an example of a control apparatus;

Figure 3 shows cells provided by a station;

Figures 4 to 8 are flowcharts according to certain examples;

Figure 9 shows an example for an information element;

Figures 10A - 10D show examples for exchange of messages between a mobility management function and a station; and

Figure 1 1 is a flowchart illustrating a functionality of a station.

Detailed description of examples

The following description gives an exemplifying description of some possibilities to practise the invention. Although the specification may refer to “an”, “one”, or “some” examples or embodiment(s) in several locations of the text, this does not necessarily mean that each reference is made to the same example of embodiment(s), or that a particular feature only applies to a single example or embodiment. Single features of different examples and embodiments may also be combined to provide other embodiments.

Wireless communication systems provide wireless communications to devices connected therein. Typically, an access point such as a base station is provided for enabling the communications. In the following, different scenarios will be described using, as an example of an access architecture, a 3GPP 5G radio architecture. However, embodiments are not necessarily limited to such an architecture. Some examples of options for suitable systems are the universal mobile telecommunications system (UMTS) radio access network (UTRAN or E- UTRAN), long term evolution (LTE), LTE-A (LTE advanced), wireless local area network (WLAN or Wi-Fi), worldwide interoperability for microwave access (WiMAX), Bluetooth®, personal communications services (PCS), ZigBee®, wideband code division multiple access (WCDMA), systems using ultra-wideband (UWB) technology, sensor networks, mobile ad-hoc networks (MANETs), cellular internet of things (loT) RAN and Internet Protocol multimedia subsystems (IMS) or any combination and further development thereof.

Figure 1 shows a schematic example of a communication system 1 comprising a radio access system or radio access network (RAN) 2. A radio access network can comprise one or a plurality of access points, or base stations 1 1 , 12 and 13. A base station may provide one or more cells 14. An access point can comprise any node that can transmit/receive radio signals (e.g., a TRP, a 3GPP 5G base station such as gNB, eNB, a user device and so forth). A large number of radio access networks can be provided in a communication system. A radio access network can comprise a number of base stations. Communication devices 15 can be located in the service area of the radio access network 2. For simplicity, only a few devices are shown. Devices 15 in cells 14 can listen to the access points 1 1 -13.

Figure 1 shows also a session management function 20. This can comprise, e.g., a Multicast/Broadcast Session Management Function (MB-SMF). A control function 10 is provide between the session management function 20 and the access nodes 1 1 , 12 and 13. This function may be provided, e.g., by an Access and Mobility Management Function (AMF). The configuration, operation and signalling of these functions will be described later in more detail, arrow 1 1 downlink signalling according to certain examples. It is noted that the wider communication system is only shown as cloud 1 and can comprise a number of other elements which are not shown for clarity. For example, various operations and functions in accordance with a 5G based system may be comprised in a terminal or user equipment (UE), a 5G radio access network (5GRAN) or next generation radio access network (NG-RAN), a 5G core network (5GC), one or more application functions (AF) and one or more data networks (DN). The 5G-RAN may comprise one or more gNodeB (gNB) or one or more gNodeB distributed unit functions connected to one or more gNodeB centralized unit functions. The 5GC may also comprise entities such as Network Slice Selection Function (NSSF); Network Exposure Function; Network Repository Function (NRF); Policy Control Function (PCF); Unified Data Management (UDM); Application Function (AF); Authentication Server Function (AUSF); an Access and Mobility Management Function (AMF); various Session Management Functions (SMF) and so on.

The communication devices 15 may be any suitable devices adapted for wireless communications. Non-limiting examples comprise a mobile station (MS) (e.g., a mobile device such as a mobile phone or what is known as a ’smart phone’), a computer provided with a wireless interface card or other wireless interface facility (e.g., USB dongle), personal data assistant (PDA) or a tablet provided with wireless communication capabilities, machine-type communications (MTC) devices, Internet of Things (loT) type communications devices, a Cellular Internet of things (CloT) device or any combinations of these or the like. The device may be provided as part of another device. The device may receive signals over an air or radio interface via appropriate apparatus for receiving and may transmit signals via appropriate apparatus for transmitting radio signals. The communications can occur via multiple paths. To enable MIMO type communications devices may be provided with multiantenna elements.

Communications device such as access points or stations, terminal devices and network functions are provided with data processing apparatus comprising at least one processor and at least one memory. Figure 2 shows an example of a data processing apparatus 50 comprising processor(s) 52, 53 and memory or memories 51 . Figure 2 further shows connections between the elements of the apparatus and an interface for connecting the data processing apparatus to other components of the device. The at least one memory may comprise at least one ROM and/or at least one RAM. The communications device may comprise other possible components for use in software and hardware aided execution of tasks it is designed to perform, including implementing the herein described features in relation to multicast/broadcast (MBS) services. The at least one processor can be coupled to the at least one memory. The at least one processor may be configured to execute an appropriate software code to implement one or more of the following aspects. The software code may be stored in the at least one memory, for example in the at least one ROM.

The following describes certain aspects, configurations and signaling for broadcast related operations using 5G terminology. 5G Multicast Broadcast Service (MBS) is a point-to-multipoint communication scheme where data can be transmitted simultaneously from a single source to multiple destinations/devices. Broadcast refers to the ability to deliver content to all users. The broadcast content may be transmitted over a broadcast area. A broadcast area is a collection of one or more network access nodes, e.g., base stations, and/or cells of base stations that are capable of delivering the same content.

A brief explanation of some aspects of broadcast session update management operations is considered next. This illustrative description is given with reference to Figure 1 where a session management function 20 can comprise a broadcast session management function, and according to a more specific example a 5G Multicast/Broadcast Session Management Function (MB-SMF). Stations 1 1 , 12, 13 broadcasting to user devises 15 can comprise radio access network base stations, for example gNBs. Messages 21 , 22 from the session management function 20 are received by an intermediate control function. Session control messages 16 are sent to at least one gNB by the intermediate control function 10. The intermediate control function can be provided by an Access and Mobility Management Function (AMF).

A general principle of broadcast services is that a Multicast/Broadcast Session (MBS) flow information is built by the Multicast/Broadcast Session Management Function (MB-SMF) and remains transparent to the Access and Mobility Management Function (AMF). The AMF manages broadcast areas and Registration Area (RA) nodes (stations such as e.g., gNBs in the 5G) which receive the broadcast at a given point in time. Section 7.3.3 of 3GPP TS 23.247 version 17.0.0 currently states that an AMF shall, when informed about a change in the broadcast area, inform the respective gNBs serving broadcast session accordingly.

A broadcast session can be updated for various reasons. The following examples relate to scenarios where an update relates to one or more broadcast areas. Information on the update is sent from the Multicast/Broadcast Session Management Function (MB-SMF) to the Access and Mobility Management Function (AMF), and further from the AMF to the Registration Area (RA) nodes, e.g., a gNB. A gNB serving the broadcast session is a gNB in which the wireless delivery function of the broadcast session is operated in at least one cell. The information depends on whether the gNB is outside of the updated broadcast area or whether the gNB is inside the updated broadcast area. Depending on the location a session release message can be sent to some gNBs and a session setup message can be sent to some others. As show in Figures 1 and 3 a gNB may comprise multiple cells 14. The broadcast areas are defined on cell level, i.e., the record of broadcast areas for a session is provided in the accuracy of cells rather than stations providing the cells. An update of the broadcast area may affect all cells of a gNB or only some cells of a gNB. For example, in Figure 3 a broadcasting area of station 1 1 may cover only cells 30, 31 and 32 but not cells 33, 34 and 35.

To address the various possible scenarios the AMF can be configured to send three different messages. A session release message can be sent if all cells of the gNB in question are outside of the updated broadcast area. A session setup message can be sent if cells of a new gNB are new to the updated broadcast area. A session update message can be sent if the changes are on the cell level of one gNB in the updated broadcast area. However, some further issues may need to be resolved to implement selection and sending of the different control messages.

To illustrate some possible issues specific example scenarios are considered next. An AMF knows only the mapping between a tracking area (TA) and gNBs while has no awareness of cell level in general. A tracking area comprises a list of cells. A broadcast area may comprise one or more tracking areas and/or one or more cells. A TA can have its own identity (TAI). More precisely, a broadcast area is made of a list of full TAs and cells of other TAs. The cells of other TAs define “partial TAs”. The MBS Information containing, e.g., the MBS quality of service (QoS) flows can be encoded within a transparent container sent by the Multicast/Broadcast Session Management Function (MB-SMF) to gNBs in a transparent way to the AMF. A change of MBS broadcast service area may result in an MBS Broadcast Session Resource Setup to some NG-RAN (Next-Generation Radio Access Network) nodes and an MBS Broadcast Session Resource Release in other NG-RAN nodes. However, the AMF behaviour how to handle an MBS broadcast session Update message (or more generally, a request to modify an MBS Broadcast context) from the MB-SMF and what information is required by the AMF to be able to handle the request is not defined. The AMF does not know whether to send NG broadcast session setup or NG broadcast session update to the involved gNBs because the AMF is currently aware only of the mapping between TAs and gNBs.

For example, as shown in Figure 1 , a TA may comprise three gNBs: gNB 11 , gNB 12 and gNB 13. If the first broadcast area contains only cells of gNB 1 1 and gNB 12 and the updated second broadcast area contains only cells of gNB 12 and gNB 13 then the AMF 10 would need to send NG broadcast session release to gNB 1 1 , NG broadcast session update to gNB 12 and NG broadcast session setup to gNB 13. If instead the first broadcast area contains cells of gNB 11 , gNB 12 and gNB 13 and the updated second broadcast area would contain different cells of same gNB 1 1 , gNB 12 and gNB 13 then the AMF should send NG broadcast session update to all gNB 11 , gNB 12, gNB 13. AMF shall be configured to differentiate between these cases.

It is noted that in the example above the AMF may receive an updated list of TAs in the broadcast session update message which is the same list of TAs as were involved in the broadcast session start message despite the broadcast area having changed. This is so because the change is at the cell I gNB internal level which is not necessarily visible to the AMF.

Another issue may occur because of the need of the AMF occasionally to translate the Broadcast session update received from a MB-SMF into an NG broadcast Session setup. The MB-SMF however should include in the broadcast session update message signalled on the control plane session management interface between the AMF and the NG-RAN (gNB), known as the N2 SM interface, a container including at least the MBS information. When the AMF receives the broadcast session update containing a list of TAs and the N2 SM container, the AMF cannot detect whether the broadcast area has been updated, the MBS Information within the N2 SM container has changed, or both.

Furthermore, if only MBS information (e.g., MBS QoS flows) has been updated, then the AMF just needs to generate NG broadcast session update messages but if the broadcast area has also changed then the AMF should generate also NG broadcast session setup or NG broadcast session release messages. The AMF cannot necessarily differentiate these two cases because the MB SMF broadcast session update request received by AMF (i.e., a request to modify an MBS Broadcast context, e.g., from the MB-SMF) may contain the same TA list even after the change.

Yet another example of an update is the opposite case where only the broadcast area is updated while the MBS Session information (e.g., MBS QoS Flows) remains the same. In that case there may be no need to include the MBS Information of the N2 SM container in the NG broadcast session update message towards gNBs which were already involved in the broadcast area before the update because they already know the MBS information. The inclusion of the container with MBS information would unnecessarily force these gNBs to check the content to detect if there is any change.

The following describes procedures how to alleviate one or more of these broadcast session update related issues. In the specific examples an AMF and gNBs can be configured to operate in efficient manner in case of MB-SMF broadcast session updates.

The flowchart of Figure 4 illustrates an example of the general principle for controlling a broadcast session in an area. In the method a message related to the broadcast session is received at 100 from a session management function. An updated information record regarding stations associated with the broadcast session is then generated at 102. In Figure 1 processor 25 can generate record 24 in memory 26, e.g., based on message 22 from the session management function or messages 17 from the stations 1 1 , 12 and 13. It is then determined at 104 whether there is a change between the updated information record 23 and an earlier information record regarding stations associated with the broadcast session. A session control message is then sent at 106 accordingly to at least one station. The updated information record generation may be performed in various manners. A possibility is to determine information by the access and mobility management function 10 for the updated record from messages 21 and 22 from the session management function 20. Another example is generation based on exchange of messages 16 and 17 with the stations. More detailed examples of this will be given below.

The session control message may comprise one of a session release message, a session setup message or a session update message.

Handling of a MBS broadcast session update message by an AMF can be provided in various manners, depending on whether the AMF receives and handles a record of cells (referred below as a list of cells) in the broadcast area or not. In accordance with an example an AMF can be configured to obtain information of the broadcasting area, including cell level information, for the information record. The AMF may then behave accordingly, e.g., selecting which control messages and to which broadcasting stations to send the messages. In another example the AMF is not provided with cell level knowledge but sends MBS related control messages that are then processed at the receiving stations. If the AMF has sent incorrect control message to any of the stations it can figure this out from the subsequently received replies from the broadcasting stations (which can analyse the broadcast area themselves) and the AMF can then update its records based on the replies.

According to a more detailed example for broadcast session update an AMF is configured to maintain an up-to-date list of gNBs serving a broadcast session at any point in time.

Figure 5 shows a flowchart for an example where messages from a MB-SMF to the AMF received can include information necessary for the AMF to be able to generate a list of all gNBs that are involved in a broadcast session. When the AMF receives a session start message a first list is generated. Whenever a session update message is received, a new or updated list is created. The previous list and the new list are compared, changes detected and the respective gNBs are informed accordingly.

An exact broadcast area containing full TAs and a list of cells can be received by the AMF in MBS broadcast session start messages and MBS broadcast session update messages from the MB-SMF. The exact broadcast area can be made visible to the AMF based on the messages and the list of cells included in this received broadcast area and can be used by the AMF in further messaging.

A MB-SMF can send a broadcast session start message to an AMF including a broadcast area and a N2 SM container. The N2 SM container can include at least MBS information (e.g., the MBS QoS flows). When the AMF receives the MB-SMF broadcast session start message the AMF can first determine the first list of involved gNBs by taking the list of gNBs which maps to the full TAs using a NG Setup request message received earlier which contains this mapping and adding the list of gNBs mapping the most significant bits of the cell IDs (Eg., Cell Global Identities; CGIs). The starting stage can more generally be where the MB-SMF requests broadcast MBS session context creation.

The AMF can then send the NG broadcast session setup to all gNBs identified as being involved gNBs. If the setup is successful, the gNB can reply with a NG broadcast session setup response. If the setup is unsuccessful the gNB can reply with a NG broadcast session setup failure. The final list of serving gNBs then includes all those involved gNBs which replied with success.

The broadcast session can then start by broadcast MBS session context creation. The AMF can keep in its memory the generated final list of current serving gNBs for the broadcast session. There are different options for a gNB to receive the broadcast area. An AMF may propagate it in the NG broadcast session setup at message level. Another option is for the broadcast area be included within the N2 SM container generated by the MB-SMF.

Similar handling can be repeated by the AMF to identify an updated list of serving gNBs after receiving an MB SMF broadcast session update message.

According to an aspect the operation can be further optimized regarding those gNBs that were on the previous list and are also on the new list, i.e., gNBs that were in the previous broadcast area and are also still in the updated broadcast area. In such case a session update message can be sent selectively such that the session update is only sent when something actually changes for that respective gNB. The change may be on cell level, i.e., when cells of that gNB are either included or excluded from the broadcast area (as this is known by the AMF with the above described procedure). But even if there are no changes on the cell level for a gNB (i.e., no changes in the broadcast area), there may still be changes in the broadcast session, i.e. changes not in the broadcast area, but in the general “MBS information” (like MBS QoS flows).

This “MBS information” is sent from MB-SMF to the gNB in a container (e.g., a N2 SM container) that is transparent to the AMF, and thus the AMF may not be able to see if the “MBS information” has been changed. The MB-SMF can address this by including a “MBS Info Update indicator” into the message which can then be detected and understood by the AMF. Based on this indicator the AMF can determine whether the “session update” message needs to be sent. In other words, when there is no change in the cell level broadcast area of a gNB (known through the procedure) and no change in the “MBS information” (known through the indicator) the AMF can refrain from sending the “session update” message.

In accordance with a more specific example, when a MB SMF sends a broadcast session update message, or more generally, the MB-SMF requests broadcast MBS session context update, the MB SMF can include the broadcast area, the N2 SM container (e.g., including at least the MBS QoS flows) and an MBS Info Update indicator in the message. The indicator parameter can be used to indicate whether the MBS information within the N2 SM Container (which as such is transparent to the AMF) has changed.

The AMF analyses the new received broadcast area and can similarly build the new updated list of involved gNBs in the broadcast session update operation using the same method as for the broadcast session start operation.

The AMF can use the new list of involved gNBs in the broadcast session update message and the list of currently serving gNBs to send NG broadcast session setup including N2 SM container to gNBs newly involved (i.e., gNBs not present in the list of currently serving gNBs), if any. The AMF can also send NG broadcast session release to gNBs no longer involved (i.e., gNBs in the list of currently serving gNBs but not present in the new list of involved gNBs in the broadcast session update), if any. A NG broadcast session update can be sent to gNBs which were already serving the session only if at least one of the two following conditions are met: the broadcast area has changed for this gNB and /or the MBS Info update indicator indicates a change of the MBS information. If none of the condition is valid, the AMF can skip sending the NG broadcast session update message to this gNB. When sent, the AMF can selectively include in the NG broadcast session update message the N2 SM container only if the MBS Info Update indicator indicates a change of MBS information and it may also include the broadcast area only if it has changed.

When the respective gNB receives the NG broadcast session update message which includes the broadcast area but not the N2 SM container, the gNB can start the broadcast session in cells newly involved using the existing MBS information and/or stop the broadcast session in serving cells no longer involved.

When the respective gNB receives the NG broadcast session update message which includes only the N2 SM container, the gNB can update the MBS broadcast delivery according to the new MBS information in currently serving cells.

When the respective gNB receives the NG broadcast session update message which includes both the broadcast area and the N2 SM container, the gNB can start MBS broadcast delivery in cells newly involved using the MBS information contained in the N2 SM container, and/or stop MBS broadcast delivery in serving cells no longer involved, and/or update the MBS broadcast delivery according to the new MBS information in serving cells which are still involved.

In another scenario illustrated in Figure 6 an AMF can have some information of mappings between TAs and gNBs but cannot interpret the full broadcast area from messages 21 and 22 of Figure 1 . The AMF only receives in a broadcast session start or a broadcast session update a list of TAs which comprise the broadcast area, i.e., a kind of superset of the broadcast area. When a broadcast session start or an update occurs in a broadcast session, the AMF can contact all gNBs from the respective TAs. The contacted gNBs can check if the broadcast area is relevant to them and reply correspondingly to the AMF. The AMF can then build a list of involved gNBs based on the responses. However, any cell info is not necessarily by the AMF. In other words, during broadcast session start all gNBs of the respective TAs are contacted, and those gNBs indicate in their reply whether they are involved or not in the broadcast area. When a session is updated, all gNBs that are not (yet) on the “confirmed involved=serving” list, but that are in the new TAs are contacted. Again, they would indicate if they are involved in the broadcast area or not. The AMF then can build a new list of involved gNBs. Involved gNBs are those identified by the received list of TAs and serving gNBs are those in the information record. The AMF can then send “release session” messages to all gNBs not anymore on the list, and potentially “update session” messages to all gNBs that were on the previous list and that still are on the new list.

A MB-SMF can send a broadcast session start message, or more generally, broadcast MBS session context create operation is invoked to the AMF including the list of involved TAs and an N2 SM container. The list can comprise full and partial TAs but the AMF does not know whether a TA is full or partial. The N2 SM container which is transparent to the AMF includes at least the broadcast area and the MBS Information. The broadcast area comprises the list of full TAs and the list of cells in partial Tas. The TA identity of these partial TA may not be included. The MBS Information comprises at least MBS QoS flows information. The AMF identifies at the list of involved gNBs as the list of all gNBs belonging to one of the involved TAs. Then the AMF sends the NG broadcast session setup message (including the N2 SM container) to all involved gNBs. Responses are then received. If a gNB is involved in the broadcast area the gNB replies with NG broadcast session setup response. If a gNB is not involved by the broadcast area the gNB reponds with NG broadcast session setup failure. The AMF can then build a final list of serving gNBs by including all those involved gNBs which have replied with success. After this the broadcast session can start, and the AMF can keep in memory this list of serving gNBs for the broadcast session.

The operation can be optimized by use of a MBS Info Update indicator as above. An “Area Change indicator” can also be introduced that can be provided on TA level in response to a change in the broadcast area on the TA level. An example of this is shown in Figure 7.

Figure 8 show yet another implementation example. In a session update operation the MB SMF sends a broadcast session update message to AMF including the new list of involved TAs and the N2 SM container. The AMF sends an NG broadcast session setup including the N2 SM container to all gNBs belonging to the new list of involved TAs which are not in the current list of serving gNBs. The AMF receives response from gNB which may be one of the following: NG broadcast session setup response whereafter the AMF adds the gNB to the list of serving gNBs or NG broadcast session setup failure whereafter the AMF does not add the gNB to the list of serving gNBs. The AMF sends an NG broadcast session release to all gNBs which are in the current list of serving gNBs and do not belong to the new list of involved TAs. The AMF sends an NG broadcast session update including N2 SM container to all gNBs which belong to the new list of involved TAs and which are also in the current list of serving gNBs.

The AMF receives response from gNB. The response may be a NG broadcast session update response including a new Remove Indicator. This is the case when all cells served by this gNB were removed from the broadcast area. The AMF removes the gNB from the list of serving gNBs. The response may also be a NG broadcast session update response which does not include a new Remove Indicator or including a new Keep indicator. In response the AMF keeps the gNB in the list of serving gNBs.

In accordance with an aspect the operation can be optimized by adding at least one specific indicator to the broadcast session update message sent by a MB SMF to an AMF. For example, an MBS Info Update indicator can be added at message level. The indicator tells the AMF whether the MBS information within the N2 SM Container (transparent to the AMF) has changed, i.e., MBS QoS flows information has changed (an MBS QoS flow is added/removed, QoS parameters changed). Another possibility is to add an area Change indicator at the TA level, i.e., which may be present associated to one or more of the TAs in the new list of involved TAs. This indicator is set by the MB SMF when the broadcast area covered by this one or more TA(s) has changed.

The behaviour of the AMF when receiving the broadcast session update message from the MB-SMF is optimized with regards to the current serving gNBs which are also in the new list of involved Tas. If the involved TA to which this gNB belongs has the Area Change indicator indicating no change and the MBS Info Update indicator also indicates no MBS information change, the AMF can avoid sending the NG broadcast session update message to that gNB.

The AMF may also forward the Area Change indicator and/or the MBS Info Update indicator, when received, to the gNB in the NG broadcast session update message for optimized handling of these messages also in the gNB.

Figure 9 shows an example of an information element including information of the MBS service area cell list. In this example cells are identified based on the NR CGI. An AMF can identify the gNBs involved by the NG CGI taking the most significant bits of the NR CGIs. For example, if cell ID is 32 bits, the 20 most significant bits of these 32 bits indicate the gNB ID to which these cells belong, and value “size=20” can be configured in the AMF so that it is able to derive itself the gNB IDs involved in a list of cells. The AMF can identify the gNBs involved by TAIs from the gNB reported TAI(s) at NG setup Request. The gNB can reply with broadcast response when at least one cell was successful in the delivery and include in the N2 container back the list of successful cells per TA together with list of successful QoS flows. The gNB replies with broadcast failure when no cell was successful.

The AMF can receive a new broadcast area in an update message. In this case the MB-SMF can include in the session update a container with the MBS information, similarly to session start. MB SMF can also include a flag whether the MBS information has changed. AMF receives the new list of TAs and new list of cells and computes the updated list of gNBs:

- For gNBs which were not delivered before, the AMF sends NG session start with broadcast area and the N2 container.

- For gNBs which were already involved, the AMF sends NG session update with broadcast area and the N2 container and the flag. gNB will start the service in new involved cells, stop in cells no longer involved. For cells already involved, gNB looks at the flag to see if update is needed.

- For gNBs which are no longer involved, AMF sends an NG Release.

Figures 10A - 10D shows examples for the messaging indicated by arrows 16 and 17 in Figure 1 and explained above. The AMF can use information from the gNB responses in generating the lists of cells, as explained above.

In Figure 10A the broadcast (BC) session setup procedure is successful. The AMF initiates the procedure by sending an broadcast session setup request message to the gNB. If the gNB accepts the broadcast session setup request, the gNB responds with the broadcast session setup response message. Figure 10B shows unsuccessful setup operation. If the gNB is not capable of correctly processing the request (e.g., the MBS resources could not be established at all in any cell), or gNB determines that not any cell of the gNB is involved by the received broadcast area, the gNB shall send broadcast session setup failure message. Figures 10C and 10D relate to broadcast Session Modification procedure to request gNB to update the broadcast area or the MBS information related to a previously established MBS session. In Figure 10C the AMF initiates the procedure by sending a broadcast session modification request message to the gNB. If the MBS Service Area IE is included in the broadcast session modification request message, the gNB shall update the MBS service area and send the broadcast session update response message. If the broadcast Session Resource Modify Request Transfer IE is included in the broadcast session modification request message, the gNB shall update the MBS context and resources and send the broadcast session modification response message. In Figure 10D, if the gNB is not capable of correctly processing the request, the gNB shall send MBS session modification failure message.

Figure 11 shows flowchart for the operation at a station within a broadcast area of a broadcasting session, e.g., station 1 1 of Figure 1 , and responding to session update messages from the intermediate control function 10. The station receives at 200 a session update message associated with the broadcast area of the broadcasting session. It can determine at 202 whether the station still is within the broadcasting area. If no, an indication is included at 204 in a session update response that the station is no longer within the broadcasting area of the broadcasting session in response to determination that the cells served by the station are no longer a part of the broadcast area of the session. If yes, the station includes at 206 in a session update response an indication that the station remains within the broadcasting area of the broadcasting session when there are still cells served by the station that are a part of the broadcast area of the session.

In some embodiment the number of NG messages can be reduced. This may be the case in particular for NG broadcast session update messages as per the example scenario provided above. In some embodiment the AMF does not need to process cell IDs to determine the serving gNBs but can derive this information from messaging to and from gNBs. In some embodiments specific indicators are provided by MB SMF to the AMF so that it does not need to process cell IDs and it can skip sending some broadcast session update messages.

It is noted that while the above describes example embodiments, there are several variations and modifications which may be made to the disclosed solution without departing from the scope of the present invention. Different features from different embodiments may be combined.

The embodiments may thus vary within the scope of the attached claims. In general, some embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. For example, some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although embodiments are not limited thereto. While various embodiments may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

The embodiments may be implemented by computer software stored in a memory and executable by at least one data processor of the involved entities or by hardware, or by a combination of software and hardware. Further in this regard it should be noted that any of the above procedures may represent program steps, or interconnected logic circuits, blocks and functions, or a combination of program steps and logic circuits, blocks and functions. The software may be stored on such physical media as memory chips, or memory blocks implemented within the processor, magnetic media such as hard disk or floppy disks, and optical media such as for example DVD and the data variants thereof, CD.

The memory may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The data processors may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASIC), gate level circuits and processors based on multi core processor architecture, as non-limiting examples. Alternatively or additionally some embodiments may be implemented using circuitry. The circuitry may be configured to perform one or more of the functions and/or method procedures previously described. That circuitry may be provided in the network entity and/or in the communications device and/or a server and/or a device.

As used in this application, the term “circuitry” may refer to one or more or all of the following:

(a) hardware-only circuit implementations (such as implementations in only analogue and/or digital circuitry);

(b) combinations of hardware circuits and software, such as: (i) a combination of analogue and/or digital hardware circuit(s) with software/firmware and (ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause the communications device and/or device and/or server and/or network entity to perform the various functions previously described; and

(c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and/or firmware. The term circuitry also covers, for example integrated device.

It is noted that whilst embodiments have been described in relation to certain architectures, similar principles can be applied to other systems. Therefore, although certain embodiments were described above by way of example with reference to certain exemplifying architectures for wireless networks, technologies standards, and protocols, the herein described features may be applied to any other suitable forms of systems, architectures and devices than those illustrated and described in detail in the above examples. It is also noted that different combinations of different embodiments are possible. It is also noted herein that while the above describes exemplifying embodiments, there are several variations and modifications which may be made to the disclosed solution without departing from the spirit and scope of the present invention.