GB2369002A

GB2369002A - Mobility management in a UMTS network

Info

Publication number: GB2369002A
Application number: GB0017311A
Authority: GB
Inventors: Keijo Tapio Laiho
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 2000-07-15
Filing date: 2000-07-15
Publication date: 2002-05-15
Anticipated expiration: 2020-07-15
Also published as: GB0017311D0; GB2369002B

Abstract

An Initial UE message is sent from the UTRAN to a node of the core network of the mobile network, the Initial UE message containing the Location Area Identity (LAI) of the serving RNC and a Service Area Identity (SAI) containing the LAI of the drift RNC. At the node it is determined whether the LAI identifies a first location area containing at least a part of a service area defined for the UE. If so, the node records that the UE is available for paging and, if the converse is true, it is determined whether the LAI of the SAI identifies a second location area containing at least a part of the service area. If the second location area does contain at least a part of the service area, the node records that the UE is available for paging and, if the converse is true, the node records that the UE is unavailable for paging.

Description

Mobility Management in a Mobile Telecommunications Network

Field of the Invention The present invention relates to mobility management in a mobile telecommunications network and more particularly to mobility management in a UMTS network.

Background to the Invention Figure 1 illustrates schematically a part of a Universal Mobile Telecommunications System (UMTS) network (UMTS is sometimes referred to as 3GPP). The network includes a core network part 1, which for the purpose of the following discussion is a circuit switched network handling for example voice calls. The core network 1 comprises UMTS Mobile Switching Centres (MSCs) which in Figure 1 are indicated generally with the reference numeral 2. (It will be appreciated that the UMTS network will also comprise a packet switched core network such as a General Packet Radio Service (GPRS) network comprising Serving GPRS Support Nodes (SGSNs) and Gateway GPRS Support Nodes (GGSNs) ). A subscriber, or more particularly User Equipment (UE) 3, is coupled to the core network 1 via an access network 4 referred to as a Universal Terrestrial Radio Access Network (UTRAN). More particularly, the MSCs 2 are connected to Radio Network Controllers (RNCs) 5,6 of the UTRAN 4 over an interface referred to as the lu interface.

Each RNC 5,6 forms part of a Radio Network Subsystem (RNSs) 7,8 which also comprises a set of Base Transceiver Stations (BTSs) 9 referred to in UMTS terminology

as Node B's. The interface between a RNC 5, 6 and a Node B 9 is known as the lub interface. A Node B 9 provides the connection point to the UTRAN 4 for a UE 3, and the interface between the Node B 9 and the UE 3 is known as the Uu interface. The RNS (for example RNS 7 in Figure 1) which connects a UE 3 to the core network 1 at any given time is referred to as the Serving RNS for that particular UE 3, whilst the RNC 6 of the serving RNS 7 is known as the Serving RNC. The serving RNC 6 controls the radio connection between the UE 3 and the UTRAN 4, and the serving RNC 6 terminates the Iu protocols for the UE 3. The serving RNC 6 is responsible for

transmitting paging messages corresponding to mobile terminating (incoming) calls to UEs. A so-called"drift"RNC (e. g. RNC 5 in Figure 1) may support a serving RNC with additional radio resources when the connection between the UTRAN and the UE requires the use of Node Bs controlled by the drift RNC (i. e. the drift RNC becomes the "access"RNC for the UE). In some circumstances a process known as serving RNS relocation may occur, in which an existing serving RNS is replaced by a drift (or "target") RNS as the serving RNS. Serving RNS relocation typically occurs when a UE which is in BUSY mode (i. e. actively involved in a circuit switched or packet switched call) roams into an area covered by a new RNC.

UMTS uses the concept of geographical location areas, each identified by a unique Location Area Identity (LAI), to locate UEs. The core networks are made aware of the current location of a UE by both periodic location updates (e. g. generated every 15 minutes) and specific location updates (associated with specific activities). When a UE terminating call is initiated, a paging message is broadcast over the current known location area of the UE. A given RNC may be responsible for a single location area, although in some cases an RNC may be responsible for multiple location areas or a single location area may be handled by two or more RNCs.

Figure 2 illustrates in very general terms the bearer structure used by UTRAN to carry user data between the UE 3 and the core network 1. When it is required to establish a user plane connection, the responsible UMSC or SGSN 2 instructs the UTRAN 4 to establish a logical connection between the UMSC or SGSN 2 and the DE 3. This logical connection is referred to as a Radio Access Bearer (RAB). The established RAB inherits requirements of the requested UMTS service, e. g. Quality of Service, etc. Based on the inherited requirements of the RAB, the serving RNC 6 establishes user plane connections with the core network 1 (i. e. UMSC or SGSN 2) and with the UE 3. The connection between the serving RNC 6 and the core network 1 is referred to as the Iu bearer whilst the connection between the serving RNC 6 and the UE 3 is referred to as the Radio Bearer (RB). Both of these bearers represent further logical channels, with the serving RNC 6 performing a mapping between them. The bearers themselves are

mapped onto appropriate traffic channels for transmission over the respective interfaces (Iu and Uu).

The concept of serving and drift RNCs creates a potential problem in so far as the UTRAN may inform the serving MSC 2 of the core network 1, that a DE is located within a particular LA (corresponding to the drift RNC 5) while in fact the serving RNC 6 which is responsible for paging the UE 3 corresponds to a different RNC (the serving RNC 6). A paging message may then be sent from the core network to the drift RNC 5 which would be unable to deal with the request. The current UMTS standards overcome this potential problem by allowing the UTRAN to"lie"when sending location information messages (i. e. RANAP InitialUE messages) to the core networkthe updates in fact contain the LAI of the serving RNC rather than that of the drift RNC.

The Visitor Location Register (VLR) associated with or integrated into the MSC 2 is updated accordingly so that subsequent paging messages for the UE can be correctly sent to the serving RNC 6, which can then"redirect"the paging request to the drift RNC 5.

Summary of the Invention Operators of future UMTS networks are likely to make use of a concept known as "service areas"to offer maximum flexibility to their customers. The service areas concept will allow operators to offer communications services to customers in specific, restricted areas. These areas may be relatively small (local) or may be regional. For example, a large corporation may have a contract with an operator which allows its employees to use the services of the operator only within the locale of the corporation's sites.

The concept as currently proposed operates as follows. When the MSC of the core network receives a location information message from the serving RNC, the MSC examines the message to determine whether or not the LAI contained in the message (and corresponding to the serving RNC) corresponds to a location area containing at least a part of the service area. If so, then the VLR of the MSC is updated to indicate that the UE may be paged for incoming calls. If the LAI contained in the message does

not correspond to a location area containing at least a part of the service area, then the VLR is updated to indicate that the DE should not be paged for incoming calls.

When an incoming call is subsequently received, and assuming that the VLR indicates that the UE can be paged, the UE is paged via the serving RNC. When the DE responds to the paging, a further location information message is sent from the serving RNC to the MSC. The location information message contains a Service Area Identity (SAI) which includes the identity of the current cell in which the mobile is located. Only if the cell lies within the service area is the call actually connected. The procedure is simpler for UE originating calls, as the initiation of a call by the UE causes a location information message, containing the LAI and SAI, to be sent from the serving RNC to the MSC. The MSC can therefore directly determine whether the UE is located within the service area and whether the call should actually be connected.

It can be envisaged that, where allowed by a network, a UE may be able to roam into and out of a service area allocated to the UE for circuit switched services while making use of packet switched services-often resulting in the allocation of a drift RNC. This situation may arise either where the packet switched services are not subject to service area restrictions or where the network does not terminate an in-use packet switched service when a UE leaves a service area (i. e. the UE is in BUSY mode for the packet switched core network).

The inventor of the present invention has recognised that, where a UE is making use of a serving RNC which does not correspond to a LA containing at least a part of the service area, but which is communicating via a drift RNC which does correspond to a LA containing at least a part of the service area, the UE may be mistakenly denied access to the incoming call. This problem is overcome by analysing the LAIs of both the drift and serving RNCs contained in location update messages.

According to a first aspect of the present invention there is provided a method of managing the mobility of User Equipment (UE) in a UMTS mobile telecommunications network where the UE communicates with a core network via a drift and a serving RNC of a UTRAN, the method comprising the steps of :

sending a location information message from the UTRAN to a node of the core network of the UMTS network, the location information message containing the Location Area Identity (LAI) of the serving RNC and a Service Area Identity (SAI) containing the LAI of the drift RNC; determining at said node whether or not the LAI identifies a first location area containing at least a part of a service area defined for the UE ; if the first location area does contain at least a part of the service area, recording at the node that the UE is available for paging and, if the first location area does not contain at least a part of the service area, determining whether or not the LAI of the SAI identifies a second location area containing at least a part of the service area; and if the second location area does contain at least a part of the service area, recording at the node that the UE is available for paging and, if the second identified location area does not contain at least a part of the service area, recording at the node that the UE is unavailable for paging.

By performing this check on both the (serving) LAI and the (drift) LAI of the SAI, networks embodying the present invention avoid mistakenly paging services to UEs.

It will be appreciated that the drift RNC and serving RNC described above may be physically separate nodes or may be logical nodes having substantially the same physical location.

The steps involving analysing the LAI (and the SAI) are preferably carried out following the receipt of an Initial UE message by the core network. Thereafter, the core network records the paging rights of the UE. These rights may be changed following receipt of a subsequent Initial UE from the UTRAN. Preferably, when a UE terminating connection is initiated, said node identifies whether or not the UE should be paged (on the basis of the previously recorded data). If the UE can be paged, a paging message sent. In the event that the UE answers the call alert, an Initial DE message is sent from the serving RNC to said node. The node then determines from the SAI contained in the Initial UE message whether or not the UE is within the service area and hence whether or not the call should be connected.

The core network may be a circuit switched core network (e. g. for carrying voice calls) or may be a packet switched core network (e. g. a GPRS core network). In the former case, said message may be a Location Update message (according to the RANAP protocol) and the node which receives this message may be an MSC. In the latter case, the node may be a SGSN or a GGSN.

According to a second aspect of the present invention there is provided a UMTS mobile telecommunications network in which a UE may communicate with a node of a core network via a drift and a serving RNC of a UTRAN, the UMTS network comprising: a first RNC operating as a serving RNC and arranged to send a location information message from the UTRAN to the core network of the UMTS network, the location information message containing the Location Area Identity (LAI) of the serving RNC and a Service Area Identity (SAI) containing the LAI of the drift RNC; a node in the core network arranged to receive said location information message and to determine whether or not the LAI identifies a first location area containing at least a part of a service area defined for the UE, if the first location area does contain at least a part of the service

area, to record at the node that the DE is available for paging and, if the first location area does not contain at least a part of the service area, to determine whether or not the LAI of the SAI identifies a second location area containing at least a part of the service area, and if the second location area does contain at least a part of the service area, to record at the node that the UE is available for paging and, if the second identified location area does not contain at least a part of the service area, to record at the node that the UE is unavailable for paging.

Brief Description of the Drawings Figure 1 illustrates schematically a UMTS network; Figure 2 illustrates schematically the bearer structure used in the UTRAN part of the UMTS network of Figure 1; and

Figure 3 is a flow diagram illustrating a location update process in a UMTS network.

Detailed Description of Certain Embodiments As discussed above with reference to Figures 1 and 2, one scenario in a UMTS network involves the DE 3 making use of the radio resources of a drift RNC 5 whilst the radio resources allocated to the UE 3 are controlled by a serving RNC 6. The serving RNC 6

negotiates radio resources with the UE 3, over the Iur interface using the Radio Resource Control (RRC) protocol (ETSI 25.331). It is assumed for the purpose of the following discussion that the UE 3 (or rather the subscriber using the UE 3) has a contract with the operator of the network under which the operator provides network services to the UE 3 when the UE is located within a particular service area (which may in fact comprise a set of local sub-areas).

Typically, when a UE 3 is turned on, the RNC 6 corresponding to the location area within which the UE 3 is located is both the serving and access RNC. At this time, the serving RNC 6 sends a location information message (RANAP InitialUE message) to the serving MSC 2 of the core network 1, and the MSC 2 checks whether or not the location area identified by the LAI contains at least a part of the service area allocated to the UE 3. Assuming that the identified location area does contain part of the allocated service area, a VLR associated with the MSC 2 is updated to record that the UE 3 may be paged for DE terminating calls. In the event that the identified location area does not contain at least a part of the allocated service area, the MSC 2 compares the LAI with the LAI contained in an SAI (see below). As there is no drift RNC as yet, these LAIs are the same. The VLR associated with the MSC 2 is updated to indicate that the UE 3 is unavailable for paging (paging related to certain services such as emergency services may remain available).

In the event that the UE 3 is engaged in a packet switched connection via a GPRS core network, i. e. is in BUSY mode, and roams into a different location area associated with a second RNC 5, it may be advised by the serving RNC (either directly or via the second RNC) that the second RNC 5 is to be the drift RNC for the UE 3. Typically, after some time interval, the UE 3 sends a periodic Location Update Request to the

serving RNC 6. The serving RNC 6 must then send an Initial DE message to the MSC 2 of the core network 1. According to the current standard, this message contains both the LAI (of the serving RNC 6) and a Service Area Identity (SAI) which contains the LAI of the drift RNC (as well as certain other information including the cell location of the DE within the location area of the drift RNC).

Upon receipt of the Initial UE message from the UTRAN, the serving MSC 2 analyses the LAI of the serving and drift RNCs to determine whether or not either corresponds to a location which is within the allocated service area. Firstly, the LAI of the serving RNC 6 is checked. If it identifies a location area containing at least a part of the service area, the VLR is updated to record that paging is active for the UE 3. If, on the other hand, the identified location area is outside of the service area, the MSC 2 compares the LAI with the LAI contained in an SAI. These will now be different, as there now exists a drift RNC for the UE 3. The MSC 2 considers next whether or not the LAI, contained in the SAI, and corresponding to the drift RNC, identifies a location area which contains at least a part of the service area. If the answer to this second question is yes, then the VLR is updated to enable paging for the UE 3 (despite the fact that the location area of the serving RNC does not contain at least a part of the service area). If the answer is no, then the VLR is updated to inhibit paging for the UE 3.

Figure 3 is a flow diagram further illustrating the method described above.

It will be appreciated by the person of skill in the art that various modifications may be made to the above described embodiment without departing from the scope of the present invention. For example, the allocation of a drift RNC may arise when a DE is BUSY with a circuit switched call, in which case the serving RNC will send a location information message to a SGSN (or GGSN) which determines whether or not paging should be enabled.

Claims

1. A method of managing the mobility of User Equipment (UE) in a UMTS mobile telecommunications network where the UE communicates with a core network via a drift and a serving RNC of a UTRAN, the method comprising the steps of : sending a location information message from the UTRAN to a node of the core network of the UMTS network, the location information message containing the Location Area Identity (LAI) of the serving RNC and a Service Area Identity (SAI) containing the LAI of the drift RNC; determining at said node whether or not the LAI identifies a first location area containing at least a part of a service area defined for the UE; if the first location area does contain at least a part of the service area, recording at the node that the UE is available for paging and, if the first location area does not contain at least a part of the service area, determining whether or not the LAI of the SAI identifies a second location area containing at least a part of the service area; and if the second location area does contain at least a part of the service area, recording at the node that the UE is available for paging and, if the second identified location area does not contain at least a part of the service area, recording at the node that the UE is unavailable for paging.

2. A method according to claim 1, wherein the steps involving analysing the LAI and the SAI are carried out following the receipt of the location information message by the core network.

3. A method according to claim 2, wherein, when a UE terminating call is initiated, said node identifies whether or not the UE should be paged on the basis of the previously recorded data and, if the UE can be paged, a paging message sent, and in the event that the DE answers the call alert, a location information message is sent from the serving RNC to said node which determines from the SAI contained in the location

information message whether or not the DE is within the service area and hence whether or not the call should be connected.

4. A method according to any one of the preceding claims, wherein the core network is a circuit switched core network.

5. A method according to any one of claims 1 to 3, wherein the core network is a packet switched core network.

6. A UMTS mobile telecommunications network in which a DE may communicate with a node of a core network via a drift and a serving RNC of a UTRAN, the UMTS network comprising: a first RNC operating as a serving RNC and arranged to send a location information message from the UTRAN to the core network of the UMTS network, the location update containing the Location Area Identity (LAI) of the serving RNC and a Service Area Identity (SAI) containing the LAI of the drift RNC; a node in the core network arranged to receive said location information message and to determine whether or not the LAI identifies a first location area containing at least a part of a service area defined for the UE, if the first location area does contain at least a part of the service area, to record at the node that the UE is available for paging and, if the first location area does not contain at least a part of the service area, to determine whether or not the LAI of the SAI identifies a second location area containing at least a part of the service area, and if the second location area does contain at least a part of the service area, to record at the node that the DE is available for paging and, if the second identified location area does not contain at least a part of the service area, to record at the node that the UE is unavailable for paging.