2.11. Signaling in GSM mobile networks

In the process of developing telephone networks, various international and national versions of telephone signaling systems were developed that ensure the transmission of control signals and interaction between network nodes in the process of servicing calls. In recent years, new network technologies have been implemented on the basis of telephone network resources and for interaction with them: for digital networks with the integration of ISDN services, cellular mobile communication networks, and intelligent networks.

To implement the corresponding services in these networks requires fast and reliable transfer of large amounts of data between network nodes. Under these conditions, one of the main directions in the development of modern digital communication networks is the use of a common channel signaling system SS№ 7, standardized for use on international and national communication networks.

In GSM mobile communication networks, two main signaling systems are adopted for exchanging information during the service of calls between network elements, as well as for interaction with other telecommunication networks: SS No. 7 (SignalingSystem No. 7 [CCITT No. 7]) and LAPD (Link Access Procedureon the D-channel (access protocol in the b channel).

The use of these two signaling systems is due to the fact that the SS # 7 signaling system, which provides signaling in digital ISDN networks, has been used for a long time to organize inter-station signaling of electronic PBXs (PBX, PABX) stationary PSTN.

In addition, in the GSM network, it is necessary to perform signaling in a point-to-multipoint configuration. The access protocol in the D-channel LAPD is specially created for this purpose, and it is widely used in the ISDN network.
Thus, the use of SS№ 7 and LAPD in the GSM network makes the GSM network compatible with the PSTN, ISDN networks, as well as with the NMT network of an analogue mobile communication system.
The operation of the SS-7 common channel signaling system is described in detail in [2.13].