DESCRIPTION OF RELATED ART UMTS is an abbreviation of Universal Mobile Telecommunications System and UTRAN is the acronym of the UMTS Terrestrial Radio Access Networks. UTRAN is a third generation mobile radio access network and is standardised by the 3GPP.

Figure 1 discloses the main nodes of UTRAN 10 and that comprises Radio Network Controllers 11, hereafter named RNC 11, and a number of node B 12 also called base stations 12.

The RNCs interface a core network 14 and a number a base stations 12, each base station 12 is however connected to just one RNC 11. Each of the base stations 12 serves mobile stations UE located within one or more corresponding geographical serving area called cells 13.

Figure 2 shows a mobile station UE with radio links established in two cells 13, this establishment of radio links in several cells 13 are referred to as macro diversity. In order to simplify, just the RNCs lla, lib corresponding to the cells 13 and not the base stations 11 actually serving the cells 13 are indicated in figure 2. It should also be noted that the connection to the mobile station UE is routed via two RNCs, one of these routes the connection to the core network 14 and is called Serving RNC lla or hereafter just SRNC lla. The second RNC llb is in charge of the cells 13 supporting the radio link to the

mobile station UE, and is called drift RNC lib or hereafter just DRNC llb.

Each mobile station UE with a subscription to the UTRAN 10 has a corresponding SRNC lla with a record of information on the mobile station UE. The mobile station UE is mobile in the geography and whenever a radio link is established in a cell handled by another RNC 11 than the SRNC 11, the communication services are routed via the SRNC lla to the DRNC llb in charge of the cell 13 and further to the mobile station UE.

A mobile station UE is in idle mode when it is being switched on and located within the service area of UTRAN 10 but having no established connection to the core network 14.

When a mobile station is in Cell PCH or URAPCH state, there is a signalling connection established between this mobile station UE and the core network 14 ; moreover, in Cell PCH the SRNC lla knows the cell 13 in which the mobile station UE is located, whereas in URA PCH the SRNC lla knows a group of cells in one of which the mobile station UE is located. A mobile station UE in idle, Cell PCH or URAPCH listens to the paging channel abbreviated PCH.

Paging is a procedure to alert a mobile station UE when there is a mobile station terminating call from the core network 14, or when there is updated system information to be read by the mobile station UE.

If initially in Cell_PCH or URAPCH mode, the mobile station UE changes state to Cell FACH during the page procedure.

In Cell FACH state the mobile station UE listens to the FACH (Forward Access CHannel), and receives signalling or user data if this data is not too extensive.

Figure 3 is a signalling diagram of the messages sent during a prior art paging procedure between the SRNC lla, DRNC

llband the mobile station UE, starting with the first messages to be sent from the top of the diagram. The page procedure relates to Radio Resource Control functions which is abbreviated RRC and are controlled by the DRNC. There is also a protocol layer called RRC for the RRC functions and that terminate in the mobile station on one end and in the DRNC lib on the other end. Hence, the base station 12 is omitted from the signalling diagram since the RRC messages are transported transparently via the base station 12.

The messages transmitted between the DRNC lib and the SRNC lla during the paging procedure relate the control signalling and are handled by the RNSAP (Radio Network Subsystem Application Part) protocol layer. The signalling diagram of figure 3 have the vertical lines indicating the respective nodes and along which the protocol layer of the respective message received or transmitted is indicated in ellipses.

Paging is triggered in the SRNC lla when there is information to be sent to the mobile station UE. In the signalling diagram of figure 3 the SRNC lla initiates the paging procedure by transmitting a"Paging Request"message to the DRNC llb. The DRNC llb then sends a"Paging Type 1" message to the mobile station UE. Upon receipt of the "Paging Type 1"the mobile station UE change state to Cell FACH and indicates this change by sending a Cell Update message in response to the DRNC llb. The DRNC llb creates a mobile station UE context, i. e. a record with information on the mobile station UE. The DRNC llb also allocates identifiers of the mobile station UE for identifying communication relating to the mobile station UE. These identifiers are C-RNTI and D-RNTI, both are described further in the preferred embodiments section of the description.

The DRNC lib informs the SRNC lla of the allocated identifiers C-RNTI and the D-RNTI by transmitting an"Uplink Signalling Transfer Indication"message including the C-RNTI and the D-RNTI. Next, the SRNC lla requests a transport channel for communication with the mobile station UE by sending a"Common Transport Channel Resource Request" message to the DRNC llb. The"Common Transport Channel Resource Request"includes a D-RNTI. Upon receipt of this message, the DRNC lib includes the C-RNTI in the MAC-C logical entity. The MAC-C and the functions handled by it are described further down in the embodiments section of this application. In respond to the prior request the DRNS llb sends a"Common Transport Channel Resource Response"to the SRNC lla.

Next, the SRNC lla sends a"Cell Update Confirm"message including the C-RNTI to the mobile station UE. The mobile station UE includes the C-RNTI in the MAC-C protocol layer and informs the SRNC lla of this by sending a"Utran Mobility Information Confirm"message. Both the"Cell Update Confirm"and the"Utran Mobility Information Confirm"are transported transparently via the DRNC llb and the radio base station 12.

SUMMARY OF THE INVENTION The radio spectrum is a scarce resource that shall be carefully utilised. It is an object of the present invention to decrease the number of messages sent during the page procedure in order to free capacity especially on the radio link that can be used for transmission of other types of information.

The present invention solves the problem by introducing C- RNTI into a Paging Type 1 message when it is sent to a mobile station that is in a Cell PCH stage. The mobile

station responds to this Paging Type 1 message by sending a Utran Mobility Information Confirm message.

An advantage with the present invention is that the Cell update procedure that is normally included in the page procedure is avoided in the inventive page procedure.

Thereby less signalling messages are sent over the radio channel. Also on the fixed links less messages are transmitted.

A further advantage is that the page procedure is faster when the cell update procedure is omitted from the page procedure.

DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram of UTRAN main nodes and their interfaces.

Figure 2 is a block diagram of nodes and networks providing a connection to a mobile station.

Figure 3 is a signalling diagram of the messages sent during a prior art paging procedure.

Figure 4 is a signalling diagram of the messages sent in the paging procedure according to the present invention.

Figure 5 is a chart of the prior art architecture of MAC protocol layer.

DESCRIPTION OF PREFERRED EMBODIMENTS The modified paging procedure of the present invention is intended for use when the mobile station (UE) is in Cell PCH state. The SRNC has information on in which cell the mobile station is located when it is in Cell PCH state.

Paging Procedure Figure 4 is signalling diagram of the messages exchanged between the SRNC lla, the DRNC lib and the mobile station UE during the page procedure of the present invention. The messages sent between the DRNC llb and the mobile station UE all belong to the RRC (Radio Resource Control) functions, and are transmitted transparently by the radio base station 12. Consequently, the radio base station is not indicated in the signalling scheme.

Paging of the specific mobile station UE is triggered in the SRNC lla when there is information to be sent to the mobile station UE. The SRNC lla sends a"Common Transport Channel Resources Request"message that includes a temporary identifier of the type S-RNTI and the identity of the cell were the mobile station resided. The cell identity is abbreviated C-ID in the specification, and will be so also in the further description The DRNC llb receives this request and the S-RNTI and C-ID included in it triggers the DRNC llb to create a mobile station context, i. e. a record of information on the mobile station UE. The S-RNTI and C-ID also triggers the DRNC lib to allocate a D-RNTI and C-RNTI as identifiers for the communication with the mobile station. The different types of temporary identifiers with abbreviations RNTI and their use are described further down. The D-RNTI and the C-RNTI are recorded in the mobile station context. The DRNC llb also includes the C-RNTI in the MAC-C protocol stack in the same way as upon receipt of any"Common Transport Channel Resources Request".

The DRNC llb sends a"Common Transport Channel Resources Response"to the SRNC lla in response to the"Common Transport Channel Resources Request". The response includes D-RNTI and C-RNTI allocated by the DRNC llb.

Next, the SRNC lla sends a"Paging Request"to the DRNC llb.

The"Paging Request"includes the C-RNTI that was previously received from the DRNC lib.

Upon receipt of the"Paging Request"the DRNC lib sends a "Paging Type 1"message to the mobile station UE. Because the"Paging Request"included a C-RNTI, the DRNC lib includes the C-RNTI in the"Paging Type 1".

The mobile station UE includes the C-RNTI in the MAC-C stack. MAC-C and its function are described further down.

The mobile station UE responds to the"Paging Type 1"by sending a"UTRAN Mobility Information confirm"message. It is a confirmation that the mobile station UE has included the C-RNTI in the MAC-C. The message is transmitted to the SRNC. The"UTRAN Mobility Information confirm"message sent during the inventive page procedure differs from that sent in the prior art paging procedure by not including a"RRC transaction identifier".

Upon receipt of the"Paging Type 1"the mobile station UE change state from Cell PCH to Cell FACH, and the"Utran Mobility Information Confirm"message sent by the mobile is a confirmation on this change of state.

RNTI (Radio Network Temporary Identifiers) RNTI (Radio Network Temporary Identifiers) are used as mobile station identifiers within UTRAN and in signalling messages between the mobile station UE and UTRAN. There are four types of RNTI: s-RNTI (serving RNC RNTI), d-RNTI (drift RNC RNTI), c-RNTI (cell RNTI) and u-RNTI (UTRAN RNTI). The s-RNTI is used by the mobile station to identify itself to the SRNC lla, by the SRNC lla to address the mobile station UE and by the DRNC llb to identify the UE to the SRNC lla.

The d-RNTI is used by the SRNC lla to identify the mobile station UE to the DRNC llb. The c-RNTI is used by the mobile

station UE to identify itself to the controlling RNC 11 and by the controlling RNC to address the mobile station UE. In the examples in this description as well as in most real cases the DRNC lla has the function of a controlling RNC.

The u-RNTI is of no interest for the present invention.

Messages and their modifications The messages sent during the inventive paging procedure are all standard messages, however, they are modified to enable the inventive paging procedure.

The messages sent between the DRNC and SRNC belong to the RNSAP protocol layer, and are standardised in the TS 25.423.

The"Common Transport Channel Resources Request"message is modified by including an information element optionally specifying the S-RNTI.

The"Common Transport Channel Resources Response"message is modified by an information element optionally specifying the D-RNTI and the"Paging Request"message is modified by an information element optionally including the C-RNTI.

The messages sent between the DRNC and the mobile station UE belong to the RRC (Radio Link Control) protocol layer and are standardised in 3GPP TS 25.331. The"Paging Type 1"is modified by optionally including the C-RNTI. The"Paging Type 1"format includes a Paging Record IE (Information Element) and the modified Paging Record is formatted: Paging Record CHOICE (Used Paging Identity) CN Identity UTRAN identity U-RNTI (Mandatory)

C-RNTI (Optionally) CN originated page to connected mode UE (Optionally) The inclusion of the information element optionally including the C-RNTI is the sole modification of the Paging Record in relation to what is specified in the 3GPP TS 25. 331.

In prior art the"RRC transaction identifier"is mandatory in"Utran Mobility Information Confirm". In the inventive paging procedure the"RRC transaction identifier"is excluded from"Utran Mobility Information Confirm"and hence it is to be a conditional information element.

MAC-C Media Access Control abbreviated MAC is a layer in the Radio Interface protocol stack. The MAC layer includes the functions for mapping logical channels to transport channels and back, this is handled in the RNC 11 in one end and at the mobile station UE at the other end.

Figure 5 is a scheme of the prior art MAC layer architecture, from the UTRAN perspective. At top figure 5 are the logical channels input/output to respective of two logical entities of MAC layer, MAC-c/sh and MAC-d in the middle of figure 3. Throughout this description the MAC-c/sh is called just MAC-C. At the bottom of figure 5 is shown the transport channels and their connections to respective of the MAC-C and MAC-d. MAC-d handles dedicated channels, however, for the present invention just the MAC-C is of interest. It handles the common channels, i. e. channels that may carry information to any mobile station within a cell, such as the paging channel (PCH) and the forward link access channel (FACH). From the UTRAN prespective there is a MAC-C entity for each cell handling all common channels.

Mobile states A mobile station may be in different states like URA PCH, Cell_PCH or Cell FACH, these states are known by the SRNC lla and correspond to the transport channel type that the mobile station UE listens to. When being in idle mode the mobile station UE listens to the PCH channel. The SRNC lla makes the mobile station UE turn into Cell FACH state by paging it and in Cell-FACH state more information may be sent. In Cell PCH state the SRNC lla knows in which cell the mobile station UE is located while in URAPCH state the SRNC just have information on a group called URA (UTRAN Registration Area) in one of which cells the mobile is located.

Additional information The signalling diagrams of figures 3 and 4 the messages are only transmitted once. They may however be repeated several times until the transmitting node has received a response from the receiving node.

In the description above, separate RNCs (11) act as SRNC (lla) and DRNC (llb), however, one RNC (11) may be in control of the base stations 12 serving the mobile station and also connecting the communication link to the core network 14.