4 Configuration of the mobile network

09.023GPPMobile Application Part (MAP) specificationTS

4.1 The entities of the mobile system

To provide the mobile service as it is defined, it is necessary to introduce some specific functions. These functional entities can be implemented in different equipment or integrated. In any case, exchanges of data occur between these entities.

4.1.1 The Home Location Register (HLR)

This functional entity is a database in charge of the management of mobile subscribers. A PLMN may contain one or several HLRs; it depends on the number of mobile subscribers, on the capacity of the equipment and on the organisation of the network. All subscription data are stored there. The main information stored there concerns the location of each MS in order to be able to route calls to the mobile subscribers managed by each HLR. All management interventions occur on this database. The HLRs have no direct control of MSCs.

Two numbers attached to each mobile subscription are stored in the HLR:

– IMSI;

– MSISDN.

The database contains other information such as:

– location information (VLR number);

– basic telecommunication services subscription information;

– service restrictions (e.g. roaming limitation);

– supplementary services; the tables contain the parameters attached to these services.

– GPRS subscription data and routeing information.

The organisation of the subscriber data is detailed in GSM 03.08.

4.1.2 The Visitor Location Register (VLR)

An MS roaming in an MSC area is controlled by the Visitor Location Register in charge of this area. When an MS appears in a location area it starts a location updating procedure. The MSC in charge of that area notices this registration and transfers to the Visitor Location Register the identity of the location area where the MS is situated. A VLR may be in charge of one or several MSC areas.

The VLR also contains the information needed to handle the calls set up or received by the MSs registered in its database (in some cases the VLR may have to obtain additional information from the HLR); the following elements can be found in its tables:

– the IMSI;

– the MSISDN;

– the TMSI, if applicable;

– the location area where the MS has been registered. This will be used to call the station;

– supplementary service parameters.

The information is passed between VLR and HLR by the procedures described in GSM 03.12.

The organisation of the subscriber data is detailed in GSM 03.08.

4.1.3 The Mobile-services Switching Centre (MSC)

The Mobile-services Switching Centre is an exchange which performs all the switching functions for MSs located in a geographical area designated as the MSC area. The main difference between an MSC and an exchange in a fixed network is that the MSC has to take into account the impact of the allocation of radio resources and the mobile nature of the subscribers and has to perform, for example, the following procedures:

– procedures required for the location registration (see GSM 03.12);

– procedures required for hand-over (see GSM 03.09).

4.1.4 The Base Station System (BSS)

The BSS is the sub-system of Base Station equipment (transceivers, controllers, etc.) which is viewed

– by the MSC through an interface (A-interface) with the functionality described in GSM 08.02;

– by the SGSN through an interface (Gb-interface) with the functionality described in GSM 03.60.

4.1.5 The Gateway MSC (GMSC)

In the case of incoming calls to the PLMN, if the fixed network is unable to interrogate the HLR, the call is routed to an MSC. This MSC will interrogate the appropriate HLR and then route the call to the MSC where the MS is located. The MSC that then performs the routing function to the actual location of the mobile is called the Gateway MSC.

The choice of which MSCs can act as Gateway MSCs is a network operator matter (e.g. all MSCs or some designated MSCs).

If the call is a voice group/broadcast call it is routed directly from the GMSC to the VBS/VGCS Anchor MSC, based on information (VBS/VGCS call reference) contained in the dialled number. See also GSM 03.68 and GSM 03.69.

See also GSM 03.04.

4.1.6 The SMS Gateway MSC

The SMS GMSC is the interface between the Mobile Network and the network that provides access to the Short Message Service Centre, for short messages to be delivered to MSs.

The choice of which MSCs can act as SMS Gateway MSCs is a network operator matter (e.g. all MSCs or some designated MSCs).

4.1.7 The SMS Interworking MSC

The SMS IWMSC is the interface between the Mobile Network and the network that provides access to the Short Message Service Centre, for short messages submitted by MSs.

The choice of which MSCs can act as SMS Interworking MSCs is a network operator matter (e.g. all MSCs or some designated MSCs).

4.1.8 The VBS/VGCS Anchor MSC

The voice broadcast/group call anchor MSC obtains from the associated GCR all relevant attributes and controls in turn all cells in its area, VBS/VGCS Relay-MSCs and dispatchers belonging to a given group call.

4.1.9 The Equipment Identity Register (EIR)

This functional unit is a database in charge of the management of the equipment identities of the MSs (see also GSM 02.16).

4.1.10 The GSM Service Control Function (gsmSCF)

This functional entity contains the CAMEL service logic to implement OSS. It interfaces with the gsmSSF and the HLR; see also TS GSM 03.78.

4.1.11 The VBS/VGCS Relay MSC

The voice broadcast/group call relay MSC obtains from the associated anchor MSC all relevant attributes and controls in turn all cells in its area belonging to a given group call.

4.1.12 The Group Call Register (GCR)

This functional unit is a database in charge of the management of attributes related to the establishment of Voice Broadcast Calls and Voice Group Calls

4.1.13 The Shared InterWorking Function Server (SIWFS)

A Shared Inter Working Function is a network function that may be used by any MSC in the same PLMN to provide interworking for a data/fax call. Whereas an IWF can only be used by its MSC, the SIWF can be used by several other network nodes e.g. any MSC within the same PLMN (the concept is not limited to a certain number of MSCs). SIWF is applied to data services in GSM Phase 2 and GSM Phase 2+ (as defined in GSM 02.02, GSM 02.03 and GSM 02.34).

The usage of an SIWF requires no additional manipulation at the MS.

An IWF provides specific functions associated with the visited MSC for the interworking with other networks. It comprises signalling and traffic channel related functions. The traffic channel related functions are provided by an Inter Working Unit (IWU).

The SIWF concept is that it provides specific functions for the interworking with other networks. It comprises signalling and traffic channel related functions. Whereas the signalling related functions are associated with the visited MSC, the IWU providing the traffic channel related functions has another physical location.

The entity that contains all additional functions needed in the visited MSC to provide the SIWF is called SIWF Controller (SIWFC). The entity where the IWU is located is called SIWF Server (SIWFS). The Interface between a visited MSC and a SIWFS is called the K Interface.

SIWFS can be provided by a MSC (MSC/SIWFS) or by another network entity (stand alone SIWFS).

4.1.14 The Serving GPRS Support Node (SGSN)

This functional unit keeps track of the individual MSs’ location and performs security functions and access control; see also GSM 03.60.

4.1.15 The Gateway GPRS Support Node (GGSN)

This functional unit provides interworking with external packet-switched networks, network screens and routing of the Network Requested PDP-context activation: see also GSM 03.60.4.2 "Configuration of a Public Land Mobile Network (PLMN)".

The basic configuration of a Public Land Mobile Network is presented in figure 4.2/1. In this figure the most general solution is described in order to define all the possible interfaces which can be found in any PLMN. The specific implementation in each network may be different: some particular functions may be implemented in the same equipment and then some interfaces may become internal interfaces. In any case the configuration of a PLMN must have no impact on the relationship with the other PLMNs.

In this configuration, all the functions are considered implemented in different equipments. Therefore, all the interfaces are external and need the support of the Mobile Application Part of the Signalling System No. 7 to exchange the data necessary to support the mobile service. From this configuration, all the possible PLMN organizations can be deduced.

Figure 4.2/1: Configuration of a PLMN

4.2 Void

4.3 Interconnection between PLMNs

Since the configuration of a PLMN does not have any impact on other PLMNs, the signalling interfaces specified can be implemented both between the entities within a PLMN and between different PLMNs.

4.4 The interfaces within the mobile service

4.4.1 Interface between the HLR and the VLR (D-interface)

This interface is used to exchange the data related to the location of the MS and to the management of the subscriber. The main service provided to the mobile subscriber is the capability to set up or to receive calls within the whole service area. To support that purpose the location registers have to exchange data. The VLR informs the HLR on the registration of an MS managed by the latter and provides it with the relevant location information. The HLR sends to the VLR all the data needed to support the service to the MS. The HLR then calls the previous VLR to inform it that it can cancel the location registration of this station because of the roaming of the mobile.

Exchanges of data may also occur when the mobile subscriber requires a particular service, when he wants to change some data attached to his subscription or when some parameters of the subscription are modified by administrative means.

4.4.2 Interface between the HLR and the gsmSCF (J-interface)

This interface is used by the gsmSCF to request information from the HLR (via the Any-time Interrogation function) or to allow call independent related network- or user-initiated interaction between an MS and the gsmSCF (via the USSD function). Support of the gsmSCF-HLR interface is a network operator option. As a network operator option, the HLR may refuse to provide the information requested by the gsmSCF.

4.4.3 Interface between the VLR and its associated MSC(s) (B-interface)

The VLR is the location and management database for the MSs roaming in the area controlled by the associated MSC(s). Whenever the MSC needs data related to a given MS currently located in its area, it interrogates the VLR. When an MS initiates a location updating procedure with an MSC, the MSC informs its VLR which stores the relevant information in its tables. This procedure occurs whenever a mobile roams to another location area. Also, for instance when a subscriber activates a specific supplementary service or modifies some data attached to a service, the MSC transfers (via the VLR) the request to the HLR, which stores these modifications and updates the VLR if required.

However, this interface is not fully operational specified. It is strongly recommended not to implement the B-interface as an external interface.

4.4.4 Interface between VLRs (G-interface)

When an MS initiates a location updating using TMSI, the VLR can fetch the IMSI and authentication set from the previous VLR.

4.4.5 Interface between the HLR and the MSC (C-interface)

When the fixed network is not able to perform the interrogation procedure needed to set up a call to a mobile subscriber, the Gateway MSC has to interrogate the HLR of the called subscriber to obtain the roaming number of the called MS (see GSM 03.04).

To forward a short message to a mobile subscriber, the SMS Gateway MSC has to interrogate the HLR to obtain the MSC number where the MS is located.

4.4.6 Interface between the MSC and the gsmSCF (L-interface)

When one of the following Supplementary Services, CD, ECT or MPTY, is invoked in the MSC a notification shall be sent towards the gsmSCF.

4.4.7 Interface between MSCs (E-interface)

When an MS moves from one MSC area to another during a call, a handover procedure has to be performed in order to continue the communication. For that purpose the MSCs involved have to exchange data to initiate and then to realise the operation.

This interface is also used to forward short messages.

This interface is also used to transfer information for inter-MSC VBS/VGCS calls.

4.4.8 Interface between the MSC and Base Station Systems (A-interface)

The description of this interface is contained in the GSM 08-series of MSs.

The BSS-MSC interface carries information concerning:

– BSS management;

– call handling;

– location management.

4.4.9 Interface between MSC and EIR (F-interface)

This interface is used when an MSC wants to check an IMEI.

4.4.10 Interface between VBS/VGCS Anchor MSC and GCR (I-interface)

This is an internal interface.

4.4.11 Interface between the MSC and the SIWF server (K-interface)

When an MSC detects that it can not provide the requested IW function, resources from an SIWF server can be used. This interface is used to allocate resources in that SIWF server and establish required physical connections to that server.

4.4.12 Interface between SGSN and HLR (Gr-interface)

The description of this interface is contained in the GSM 03.60.

4.4.13 Interface between SGSN and SMS-GMSC or SMS-IWMSC (Gd-interface)

The description of this interface is contained in the GSM 03.60.

4.4.14 Interface between GGSN and HLR (Gc-interface)

The description of this interface is contained in the GSM 03.60.

4.4.15 Interface between SGSN and EIR (Gf-interface)

The description of this interface is contained in the GSM 03.60.

4.4.16 Interface between SGSN and BSC (Gb-interface)

The description of this interface is contained in the GSM 03.60.

4.4.17 Interface between SGSN and MSC/VLR (Gs-interface)

The description of this interface is contained in the GSM 09.18.

4.5 Splitting of the data storage

The data attached to management, operation and location of each MS are stored in the Location Registers. Some data are duplicated in the HLR and in the VLR, but others may be stored only in one place.

A detailed description of the data organisation can be found in GSM 03.08.