Mobile services switching center

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A mobile services switching center ( MSC ; German: exchange in mobile networks ) means a component of a GSM - UMTS - or LTE - mobile network .

Position of the MSC in the cellular network

The MSC is a fully digital exchange in the cellular network. It represents the interface between the radio network ( Base Station Subsystem , BSS) and the fixed telephone network. It is therefore the central network element in the Network Switching Subsystem (NSS).

Each MSC is assigned a specific part of the cellular network with all Base Station Controllers (BSC) and downstream Base Transceiver Stations (BTS) that handle and control the radio traffic.

For all connections that come from or go to this part of the network, the MSC takes over the complete call management, location monitoring and also the authorization check (authentication) of the mobile station . In addition, call data is recorded for each call for charging purposes.

In addition, an MSC has interfaces to the other MSCs in the cellular network as well as to other components of the cellular network such as Home Location Register (HLR), Signaling Transfer Point (STP) , Service Control Point ( SCP ), Short Message Service Center ( SMSC ) and Voice Mail Switching Center (VMSC) ( mailbox ), which interact with the MSC to carry out tasks or to supply it with certain requirements and data.

As “Gateway MSC” (GMSC), MSCs have additional or exclusive (without BSS) interfaces to other telephone networks. These can be interfaces to other cellular networks or connections to the landline telephone . In principle, every MSC can also be a GMSC at the same time.

Each MSC has a so-called Visitor Location Register (VLR) , in which the data and the whereabouts of the subscribers who are currently in the area of ​​influence of the MSC are stored. If a subscriber comes into the sphere of influence of an MSC with his mobile radio device, his location is reported in the central subscriber database, the Home Location Register (HLR). On the other hand, all subscriber data are loaded from the HLR into the VLR of the MSC.

Mediation scenarios

Mobile Terminated Call (MTC)

If a mobile radio subscriber is called, the HLR assigned to it is first determined in which MSC catchment area the subscriber is located and the call is switched through to the corresponding MSC. The MSC then locates the location area in which the subscriber is and sets up the call to the subscriber with the help of the assigned radio network elements BSC and BTS.

Mobile Originated Call (MOC)

If a mobile subscriber calls, the MSC uses the dialed number to analyze the type of subscriber being called (mobile subscriber in your own network, mobile subscriber in an external network, landline subscriber, special call number) and sets up the call to the subscriber: For mobile subscribers, first inquired at the home HLR of the called subscriber in which network and in which MSC area he is currently located; For landline subscribers and special numbers, the call is forwarded to the landline.

Number portability

These scenarios have become correspondingly more complicated due to the introduction of the option to keep the assigned phone number even when changing providers or network operators. Since then, it has no longer been possible to decide which network a subscriber belongs to based on the network code . This requires a query in a special subscriber database , the so-called Network Address Register. This database is located either on central network elements such as the Signaling Transfer Point (STP) or on network elements for service management such as the Service Control Point (SCP).

Recent developments

3GPP Release 4

With the 3GPP specification for Release 4, the function of the MSC was divided into 2 systems:

Mobile Switching Center Server (MSS)

The MSS contains all functions for controlling the radio network, which the MSC also contains. The functions of the MSS are

  • Location management of the participants
  • Local administration of participant profiles ( Visitor Location Register (VLR) )
  • Control of call establishment and clearing
  • Collection of call data for billing purposes
  • Communication with other components of the cellular network

The MSS is used to control the cellular network . It only has signaling interfaces to other cellular network elements, to the radio network and to the media gateway, which directs the cellular data streams (voice, GPRS data).

Media Gateway (MGW)

The data streams of the cellular network (voice, data) are routed via the media gateway. The control and guidance of the data streams is taken over by the MSS. The MSS specifies to the MGW exactly which data stream is to be routed from which input channel to which output channel.

LTE networks

In LTE networks, the function of the MSC is taken over by the IP Multimedia Subsystem (IMS).

See also

Individual evidence

  1. 3GPP TS 23.002: Network architecture, chap. The Mobile-services Switching Center (MSC) ( English , ZIP / DOC; 2.8 MB) September 29, 2009. Accessed December 14, 2009.
  2. TS GSM 03.02: Network Architecture, chap. 3.3: The Mobile Services Switching Center ( English , ZIP / DOC; 691 kB) January 1, 1995. Accessed December 14, 2009.
  3. 3GPP TS 23.205: Bearer-independent circuit-switched core network; Stage 2 ( English ) Retrieved March 23, 2014.