As a result there is a need to support the emerging 3rd generation services on the evolved 2"d generation (2G) network. As a result of the separate development of data and voice communication, their modes of operation are quite different, so there is a need to find a way of supporting both types of service in mobile phone communication. One particular example of this is that the standardisation body for Global System for Mobile communications (GSM) /Enhanced Data rates for GSM Evolution (EDGE) Radio Access Network (GERAN), has recently been pursuing the support of streaming and conversational services in the packet switched (PS) domain. In order to provide a similar level of functionality to that provided for conversational services in the circuit switched (CS) domain, new mechanisms must be introduced in the PS domain.

In accordance with the present invention, a method of controlling communication in a cellular communication system comprising a mobile station and a base station comprises allocating a first unique mobile station identifier in a first domain of operation; allocating a second unique mobile station identifier in a second domain of operation; passing the first and second identifiers to the base station; correlating the first identifier with the second identifier in the base station; monitoring at the base station for pages in the second domain during transmissions in the first domain; and signalling to the mobile station, via a connection in the first domain, that there is a transmission in the second domain waiting; wherein the mobile station signals the first and second identifiers to the base station at establishment of resources in the first or second domain of operation.

The mobile passes identifiers for each domain type to the base station, where they are correlated, so that if a paging message is sent in the second domain, during a transmission in the first domain, the base station associates these and signals to the mobile station through the channel on which the transmission in the first domain is taking place, so reducing complexity and ensuring that the notification gets through. The established resources may be dedicated resources or shared resources, also used for other functions.

Preferably, the correlation is carried out by a radio resource manager in response to notification from the mobile station of each mobile station identifier.

Preferably, the first domain is a packet switched domain and the second domain is a circuit switched domain.

The method is applicable to any mobile communication system where voice and data are treated substantially independently, for example D-AMPS, but preferably, the communication system comprises GERAN.

An example of a method of controlling communication in a cellular communication system according to the present invention will now be described with reference to the accompanying drawings in which: Figure 1 illustrates a conventional paging arrangement in packet switched and circuit switched domains; Figure 2 illustrates an alternative method of paging co-ordination ; and, Figure 3 illustrates a method of controlling communication according to the present invention.

Fig. 1 shows a standard set-up for a mobile station to receive paging messages from either a circuit switched (CS) or packet switched (PS) domain. A mobile station (MS) 1 communicates with a base station subsystem (BSS) 2 over a radio link 3. The BSS 2 is connected to networks in circuit switched and packet switched domains. An interface 4 between the BSS and a mobile switching centre (MSC) 5 of the circuit switched domain is known as the A interface and an interface 6 between the serving GPRS support node (SGSN) 7 of the packet switched domain and the BSS is known as the Gb interface. If there is a call for the MS from the MSC, then a CS page is sent via the A interface 4 to the BSS 2. If the MS 1 is idle at that time, i. e. there is no on-going call, then the MS will be monitoring the relevant common control channel for paging messages addressed to it. If the call was in the PS domain, then the paging message would be sent via the Gb interface. This is straightforward and on receipt of the page, the BSS will set up a link to the MS, so that the call can be connected. A temporary mobile station identifier (TMSI) is allocated in the circuit switched domain and a packet TMSI (P-TMSI) in the packet switched domain during an attach procedure. These are derived quite differently in both cases and have no relationship to each other at all.

Generally, the TMSI is set up when the MS 1 is switched on and remains allocated until the MS is switched off again, whereas the P-TMSI may be allocated when the mobile is switched on or when the user indicates to the network that it requires general packet radio service (GPRS) services. The temporary identifiers remain valid until the mobile initiates a detach procedure which normally occurs when the mobile is switched off.

However, there are problems with the paging arrangement if the MS already has a call or session running. Conventionally, this would mean that any MS with currently allocated dedicated packet resources must also monitor the appropriate common channel for CS paging messages, or else the MS may miss out on notification that a CS call is waiting. Monitoring two channels leads to additional complexity, which is undesirable, so to avoid this, it is necessary for the relevant paging message to be directed onto the current traffic channel. One method that has been proposed for this is network mode of operation 1 (NMO 1). The CS and PS paging messages from the serving GPRS support node (SGSN) address the MS via the international mobile station identifier (IMSI) which is a globally unique identifier known in both the CS and PS domains. Thus, if there is a PS call in progress, then a paging message for a CS call from the MSC 5 is routed via the SGSN 7, as shown in Fig. 2. This routing is via an interface 8 between the MSC and SGSN known as the Gs interface and thereafter, both the PS and CS paging goes via the Gb interface. A problem with this proposal is that the Gs interface in the core network is an optional interface and cannot be guaranteed to be present.

Another suggestion to avoid the need to monitor an additional channel is to use the arrangement of Fig. 1 and to force the MSCs and SGSNs to always send the IMSI, which is a common reference in both domains, in the CS and PS paging messages. This has problems in respect of security, since if the IMSI were sent with every message, it would make it easier for one person's calls to be tracked, so currently this type of use of the IMSI is limited. Transmitting the IMSI over the radio link is avoided and it is preferred not to send it in signalling messages. Another, though lesser, drawback is that the IMSI is larger than the TMSI or P-TMSI.

Thus, the present invention focuses on the providing a new mechanism in the BSS for paging co-ordination, as the other solutions proposed do not provide a universal solution. The provision of real-time services, e. g. conversational, in the PS domain using either dedicated or shared packet channels gives rise to this requirement with respect to paging. If a CS domain page is sent to the MS whilst it has a dedicated PS resource for an on-going call/session, there is currently no mechanism available to allow the paging message to be redirected to an"in-band"signalling channel. If an IMSI is not present in a paging message from the MSC, and the MS is attached to a dedicated channel over which PS services are being provided, a radio resource management (RRM) entity in the BSS is unable to determine that the MS should be paged on the signalling channel associated with the aforementioned PS dedicated resource. Instead, the RRM will incorrectly assume that the MS should be paged on the common control channels since it has no knowledge of the identities which are correlated with the P-TMSI assigned to the MS. This may lead to the MS not receiving an indication of all incoming CS calls and hence a loss of revenue for mobile network operators, as well as customer dissatisfaction.

The method of the present invention is illustrated in Fig. 3. It is assumed that a separate RRM function exists in the BSS to control the dedicated resource in the PS domain for PS conversational services. The RRM function is subservient to the main radio resource (RR) function that already exists in current BSSs. In order to provide a paging co-ordination in the BSS for the MS, the MS signals 9 the temporary identifiers that are used to page it in the CS domain (e. g. TMSI) and in the PS Domain (e. g. P- TMSI) to the BSS at establishment of the dedicated resources. The entity responsible for RRM can pass this mapping on to RR where any CS paging message for the TMSI can be associated with the MS and can therefore be placed on the relevant in-band channel 10 for sending. The invention relies on the MS, when it moves to a PS dedicated channel controlled by RRM procedures, signalling to the RRM entity, which has knowledge of the MS P-TMSI, the value of the TMSI which RR in the BSS uses to identify the MS.

The RRM in the BSS can then pass the TMSI of the MS 1 to the RR entity in the BSS 2 and create a mapping between TMSI and P-TMSI in it's own database, so that the TMSI is co-ordinated with the dedicated channel. Any pages from the CS domain containing that TMSI are passed from RR to RRM, which can then identify where to send the paging message. In another embodiment, the RRM passes the TMSI and the P- TMSI to the RR entity in the BSS 2 so that the RR entity can determine the P-TMSI of any incoming CS page and inform the RRM entity of any required information.

Alternatively, the RRM indicates to the RR that all incoming CS pages should be passed to the RRM entity before being acted upon, to allow the RRM entity to check that an incoming page is not destined for an MS attached to a PS dedicated channel.

If the mobile moves out of range of a particular MSC or SGSN, then the TMSI or P-TMSI will change, but there is still an association in the core network which allows the MS to inform the BSS of the new TMSI or P-TMSI and which old one it replaces, so the correlation step is still possible. A new procedure is required, for the MS to BSS communication, to include the message from the MS giving the TMSI or P-TMSI data, but this message is only in the form of a short signalling message, which is sent occasionally and so it does not require significant additional resources.

The present invention provides a means of routing paging information sent from the circuit switched domain core network onto an in-band channel in an existing packet switched call or session for GERAN. The mobile will send its CS temporary identifier to the radio access network when a PS conversational call is established. The radio access network can then map the PS domain temporary identifier with the CS domain temporary identifier and therefore be able to redirect the CS domain paging message to the mobile over an in-band channel within the PS traffic channel. This avoids the mobile having to monitor one of the common broadcast channels at the same time as it uses the traffic channel.

It avoids the need for the MS to monitor both the traffic channel and the paging channel at the same time and so reduces complexity and power requirements in the mobile. This is done by enabling the BSS to be able to determine the state of the mobile and correlate the identifiers used to the MS despite the fact that the TMSI and PTMSI have no relationship when created.