介绍了第三代移动通信系统中Release 5版本IP多媒体子系统的网络构架、QoS和业务,对IM系统中各个网络实体的功能进行了简单的描述,对IM与SIP软交换的结合以及承载在IP网络上所需的QoS进行了探讨,并介绍了可以承载在IM系统上的各种业务,最后,对GGSN如何适应IM系统业务这一关键技术进行了简单介绍。 This paper introduces the network architecture, QoS and services of the Release 5 version of the IP Multimedia Subsystem in the 3G mobile communication system. It simply describes the functions of each network entity in the IM system. The combination of IM and SIP softswitch, IP network on the required QoS were discussed and introduced on the IM system can be carried on a variety of business, and finally, on how to adapt GGSN IM system business this key technology is briefly introduced.