s and the Figure 47.9. The mobile station comprises a mobile equipment and signalling data is inserted into these slots and extracted by the a subscriber identity module (SIM). In addition to these functional receiver which also time expands the speech back to its original entities, GSM also defines several interfaces, the Radio Interface form. (Um), the interface between the MSC and BSC interface) and the This continuous signalling serves several purposes: signalling interface which allows roaming between networks. This is based on the CCITT No.7 signalling standard and is defined as a It allows the base station to send power control and handover Mobile Application Part (MAP). messages to the mobile without disturbing the voice channel. The BTS and BSC together form the Base Station Subsystem The data is checked for jitter, and thereby the quality of the (BSS) and carry out all the functions related to the radio channel channel can be determined in order to indicate the need for a management. This includes the management of the radio channel handover. configurations, allocating radio channels for speech, data and sig- 47/10 Cellular radio systems Fixed telephony Mobile networks Network management MS Mobile Station VLR Visited Location Register MSC Mobile Switching Centre HLR Home Location Register BTS Base Transceiver Station EIR Equipment Identity Regsiter BSC Base Station Controller AUC Authentication centre Figure 47.9 GSM architecture nalling purposes, and controlling frequency hopping and power techniques and operating in the 900MHz band. The CEPT have control. The BSS also includes, as does the MS, the speech encoding made available two frequency bands to be used throughout Europe and decoding, and channel coding and decoding. by the GSM system, namely; The MSC, VLR and HLR are concerned with mobility manage- 1. 890MHz to 915MHz for the mobile to base station (uplink) ment functions. These include authentication and registration of the direction. mobile customer, location updating, and call set up and rele