Digital Cellular Telecommunications System (Phase 2+); Base Station Controller - Base Transceiver Station (BSC - BTS) Interface; Layer 2 Specification (GSM 08.56 Version 6.0.0 Release 1997)
The present document specifies the link layer used for signalling on the A-bis interface between BSC and BTS. The use and general aspects of the A-bis interface are described in GSM 08.51 and the interface aspects in GSM 08.52. The Link Access Procedure on the D-chamel (LAPD) specification used on the A-bis interface in the GSM PLMN is a subset of the ETS 300 125 which in hm has less options than the CCIT? Recommendation Q.921. This description contains fust the protocol definitions and second the services provided by the layer 2 to the layer 3.