本欧洲电信标准（ETS）详细描述了GSM PLMN中使用的切换程序。如本规范所述，切换程序的目的是确保在MS从一个BSS区域移动到另一个BSS区域时保持与MS的连接。本规范考虑以下两种情况:i）连接到同一MSC的基站之间的切换，这称为MSC内切换。ii）连接到不同MSC的基站之间的切换，这被称为MSC间切换。这一类别可细分为三个进一步的程序:a）基本MSC间切换程序，其中MS由控制MSC（MSC）移交- A） 另一个MSC（MSC-B）；b） 随后的MSC间切换过程，其中MS从MSC-b切换到第三个MSC（MSC-b）；c） 随后的MSC间传回，其中MS从MSC-B传回给MSC-A。在这两种情况下，i）和ii）应分别在A接口和无线电接口上使用TS GSM 08.08和TS GSM 04.08中定义的相同程序。在情况ii）中，移交程序应在MSC-A和MSC-B之间传输技术规范GSM 09.02移动应用部分（MAP）中所述的A接口消息。GSM 08系列技术规范中描述了BSS和MSC之间的分离功能。 GSM 09.10技术规范中描述了GSM 09.02协议和GSM 08.08协议之间的互通。在同一MSC上发生的切换称为MSC内切换；这包括基站间切换和基站内切换。该技术规范还涵盖了在MSC-A和MSC-B之间没有电路连接的定向重试ANI切换的要求。本技术规范不考虑在相同BSS（BSS内切换）或分组无线电服务的切换之间的无线信道之间的切换的情况。MSC间的移交对系统造成了一些限制。跨MSC移交后: -不支持呼叫重建。TS GSM 09.08中给出了MSC间切换期间和之后支持的GSM 08.08功能列表。在MSC间切换的情况下，一个MSC可能使用的第一阶段BSSMAP协议和电子接口上的第二阶段MAP协议中使用的第二阶段BSSMAP协议之间的互通由该MSC执行。注:本技术规范中SDL图表和消息流中使用的消息原语名称不代表GSM 04和GSM 08系列中规定的实际消息或GSM 09系列技术规范中规定的服务。原始名称仅用于说明其在本文件中的用途。

This European Telecommunication Standard (ETS) contains a detailed description of the handover procedures to be used in GSM PLMNs. The purpose of the handover procedures, as described in this specification, are to ensure that the connection to the MS is maintained as it moves from one BSS area to another. This specification considers the following two cases: i) Handover between Base Stations connected to the same MSC, this is termed an Intra-MSC handover. ii) Handover between Base Stations connected to different MSCs, this is termed an Inter-MSC handover. This category can be sub-divided into three further procedures: a) the Basic Inter-MSC Handover procedure, where the MS is handed over from a controlling MSC (MSC-A) to another MSC (MSC-B); b) the Subsequent Inter-MSC Handover procedure, where the MS is handed over from MSC-B to a third MSC (MSC-B ); c) the Subsequent Inter-MSC handback, where the MS is handed back from MSC-B to MSC-A. In both cases i) and ii) the same procedures as defined in the TS GSM 08.08 and the TS GSM 04.08 shall be used on the A-interface and on the Radio Interface, respectively. In case ii) the handover procedures shall transport the A-interface messages between MSC-A and MSC-B described in the Mobile Application Part (MAP), Technical Specification GSM 09.02. The split in functionality between the BSS and MSC is described in the GSM 08 series of Technical Specifications. The interworking between the GSM 09.02 protocol and the GSM 08.08 protocol is described in the GSM 09.10 Technical Specification. Handovers which take place on the same MSC are termed Intra-MSC handovers; this includes both Inter-BSS and Intra-BSS handovers. This technical specification also covers the requirements for directed retry ani the handover without a circuit connection between MSC-A and MSC-B. This technical specification does not consider the case of handovers between radio channels on the same BSS (Intra-BSS handover) or the handover of packet radio services. Inter-MSC hand-over imposes a few limitations on the system. After inter-MSC hand-over: - call re-establishment is not supported. The list of GSM 08.08 features supported during and after Inter-MSC handover is given in TS GSM 09.08. In the Inter-MSC handover case, the interworking between a Phase 1 BSSMAP protocol possibly used by one MSC and the Phase 2 BSSMAP protocol used in the Phase 2 MAP protocol on the E-interface is performed by this MSC. NOTE: The message primitive names used in the SDL diagrams and message flows in this technical specification do not represent the actual messages specified in the GSM 04 and GSM 08 series or the services specified in the GSM 09 series of technical specifications. The primitive names are only intended to be indicative of their use in this document.