4 3GPP system domains and subsystems

23.2213GPPArchitectural requirementsRelease 17TS

4.1 Allowed network and terminal configurations

A 3GPP network is divided into a radio AN and a CN, which are connected via an open interface over the Iu or S1 or A/Gb reference point(s). The A/Gb mode is not further described in this specification. Furthermore, the core network is from a functional point of view divided into a PS Domain, IM Subsystem and a CS Domain (see TS 23.002 [1]). Any deployment of the IM subsystem requires a PS domain.

The following network configurations shall be allowed:

a) networks which provide the functionality of CS Domain and PS Domain (and optionally IM Subsystem);

b) networks which only provide the functionality of the CS Domain (only with GERAN or UTRAN access);

c) networks which only provide the functionality of the PS Domain (and optionally IM Subsystem).

The following terminal configurations shall be allowed:

a) terminals which are able to access both to the CS Domain and PS Domain (and optionally IM Subsystem);

b) terminals which are only able to access to the PS Domain (and optionally IM Subsystem);

c) terminals which are only able to access to the CS Domain.

It shall be noted that a terminal which is only able to access to e.g. the PS Domain supports only mobility management, protocols etc. of that domain. The different configurations given above shall not prevent CS-type services from being delivered over the PS domain.

4.2 Circuit switched (CS) core network domain

4.2.1 Iu mode to Iu mode handover for circuit switched services

For Iu mode to Iu mode Inter-MSC Hand-Over / SRNS relocation the MAP E interface transporting RANAP messages shall be used. Alternatively, in the case of intra-PLMN handover, the GSM to UMTS inter-system handover or SRNS relocation between two MSC-areas may be executed as intra-MSC inter-system handover or SRNS relocation respectively. In such a case this will be performed by utilising a direct SCCP connection between the target RNC located in the target MSC-area and the MSC server already involved in the call.

For handover of circuit-switched services involving the change of CN equipment (only CS-MGW or CS-MGW and MSC-server) the anchor principle shall be applied.

– The first MSC Server involved in a call will become the Anchor MSC Server for this call during and after handover, and will remain in the call until the call is released. Every subsequent handover (Intra and Inter) will be controlled by this MSC Server.

– The first CS-MGW involved in a call will become the Anchor CS-MGW for this call during and after handover , and will remain in the call until the call is released. The Nc interface is anchored in the CS-MGW, the correlation between CS-MGW to PSTN and the CS-MGW to RAN remain fixed until the call is released.

4.2.2 A mode to Iu mode handover for CS services

For A mode to Iu mode inter-system Inter-MSC Hand-Over (GSM to UMTS) the MAP E interface transporting BSSMAP messages shall be used. As a network option, in the case of intra-PLMN inter-system handover from A mode to Iu mode, the handover between two MSC-areas may be executed as:

– intra-MSC handover, if the serving BSS is connected to the Anchor MSC; or

– subsequent intra-MSC handover or subsequent inter-MSC handover back to the Anchor MSC Server, if the serving BSS is connected to an MSC-B. The decision between these two alternatives is implementation and network configuration dependent.

The procedure will be performed by utilising a direct SCCP connection between the target RNC located in the target MSC-area and the Anchor MSC or MSC-B, respectively.

4.2.3 General principles for use of CS-MGW resources

The following principles for use of CS-MGW resources apply:

1. it shall not be necessary to have the CS-MGW co-located with the MSC Server;

2. the CS-MGW resources need not be associated with any particular MSC Server (see note 1);

3. it shall be possible for any MSC Server to request resources of any CS-MGW in the network (see note 1);

4. it shall be possible for an RNC to connect to the CS-MGW indicated by the MSC server;

Note 1: For points 2 and 3 above, issues related to O&M procedures such as where notification of restart of a CS-MGW should be sent to, need to be considered. Extensions to H.248 may be required.

The specification of the Bearer Independent CS CN which uses the CS-MGW is in TS 23.205 [14].

4.2.4 Transcoder location

The transcoders are located in the core network. They may be located in the CS-MGW at the border to the RAN (i.e. the CS-MGW at the Iu interface) or at the CS-MGW at the edge of the core network (e.g. at the edge towards the PSTN/ISDN), TS 23.153 [13].

4.3 Packet Switched (PS) core network domain

The requirements for the GPRS PS domain are in TS 23.060 [2] and for the EPS PS domain in TS 23.401 [27].

4.4 IP Multimedia subsystem (IMS)

The requirements for the IMS are in TS 23.228 [11].

4.5 Cross Core Network Domain Requirements

The specifications shall support the option of IP transport for the MAP and CAP based interfaces

4.6 UTRAN

The requirements for the UTRAN are in the 3GPP 25-series of specifications. An overview can be found in TS 25.401 [18].

4.7 GERAN

The requirements for the GERAN are in TS 43.051 [12]

4.8 E-UTRAN

The requirements for the E-UTRAN are in the 3GPP 36-series of specifications. An overview can be found in TS 36.300 [28].

4.9 Access to Restricted Local Operator Services

Service requirements of Restricted Local Operator Services are defined in TS 22.101 [40].

Procedures and requirements for EPS functions to support Restricted Local Operator Services are defined in TS 23.401 [27] and for IMS functions are defined in TS 23.228 [11].

Additional architectural requirements are the following:

– Access to Restricted Local Operator Services is supported for both non-IMS and IMS services.

– When Restricted Local Operator Services are accessed via IMS:

1) There is no requirement of any specific support for location over and above what is defined in TS 23.228 [11] already;

2) There is no requirement of any specific support regarding call back to the user that has initiated the session.

– Only UE-originated RLOS requests are supported and there is no support for mobile terminated services.

– Handover between 3GPP and non-3GPP accesses are not supported for UEs attached for RLOS.

– The use of Restricted Local Operator Services does not impact the ability of serving PLMN to support Lawful Interception.