The rapid development of the communication network and the increasing popularization of service level agreement(SLA)make it possible that we transmit realtime service in the connectionless IP packet network.

• 各种通信网的迅猛发展，尤其是业务级别协定(SLA)的日益普及，使得在无连接的IP分组网上传输实时业务已初现端倪。