The MSC sets up and releases the end-to-end connection, handles mobility and hand-over requirements during the call and takes care of charging and real-time prepaid account monitoring.
In the GSM mobile phone system, in contrast with earlier analogue services, fax and data information is sent digitally encoded directly to the MSC.
There are various different names for MSCs in different contexts which reflects their complex role in the network, all of these terms though could refer to the same MSC, but doing different things at different times.
However, some manufacturers design dedicated high capacity MSCs which do not have any base station subsystems (BSS) connected to them.
MSS and media gateway (MGW) makes it possible to cross-connect circuit-switched calls switched by using IP, ATM AAL2 as well as TDM.
However, modern MSS and MGW devices mostly use generic Internet technologies and form next-generation telecommunication networks.
Another important item of data associated with the SIM are the MSISDNs, which are the telephone numbers used by mobile phones to make and receive calls.
Examples of other data stored in the HLR against an IMSI record is: The HLR is a system which directly receives and processes MAP transactions and messages from elements in the GSM network, for example, the location update messages received as mobile phones roam around.
There is an additional form of identification check performed on the serial number of the mobile phone described in the EIR section below, but this is not relevant to the AuC processing.
Proper implementation of security in and around the AuC is a key part of an operator's strategy to avoid SIM cloning.
This Ki is never transmitted between the AuC and SIM, but is combined with the IMSI to produce a challenge/response for identification purposes and an encryption key called Kc for use in over the air communications.
When a particular IMSI requests access to the GSM core network, the MSC sends the RAND part of the triplet to the SIM.
An A3/A8 algorithm is implemented in Subscriber Identity Module (SIM) cards and in GSM network Authentication Centers.
Development of A3 and A8 algorithms is considered a matter for individual GSM network operators, although example implementations are available.
Data stored include: The primary functions of the VLR are: EIR is a system that handles real-time requests to check the IMEI (checkIMEI) of mobile devices that come from the switching equipment (MSC, SGSN, MME).
The answer contains the result of the check: The switching equipment must use the EIR response to determine whether or not to allow the device to register or re-register on the network.
When the legislative framework for blocking registration of devices in cellular networks appears in the country, the telecommunications regulator usually has a Central EIR (CEIR) system, which is integrated with the EIR of all operators and transmits to them the actual lists of identifiers that must be used when processing CheckIMEI requests.
The most common suppliers of individual EIR systems (not as part of a complex solution) are the companies BroadForward, Mahindra Comviva, Mavenir, Nokia, Eastwind.
According to U.S. law, which has also been copied into many other countries, especially in Europe, all telecommunications equipment must provide facilities for monitoring the calls of selected users.