本全球移动通信系统技术规范（GTS）规定了用于在基站控制器（BSC）和基站收发站（BTS）之间的A-bis干扰上发送信号的链路层。GSM 08.51中描述了A-bis接口的使用和一般方面，GSM 08.52中描述了接口方面。GSM PLMN中A-bis接口上使用的D信道（LAPD）规范上的链路接入程序是ETS 300 125的一个子集，而ETS 300 125 w的选项又比CCITT建议Q.921少。本说明首先包含协议定义，第二个包含第二层向第三层提供的服务。

This Global System for Mobile communications Technical Specification ( GTS) specifies the link layer used for signalling on the A-bis interfa ce between Base Station Controller (BSC) and Base Transceiver Station (BTS). The use and general aspects of the A-bis interface are describe d in GSM 08.51 and the interface aspects in GSM 08.52. The Link Access Procedure on the D-channel (LAPD) specification used o n the A-bis interface in the GSM PLMN is a subset of the ETS 300 125 w hich in turn has less options than the CCITT Recommendation Q.921. This description contains first the protocol definitions and second th e services provided by the layer 2 to the layer 3.