1.查询功能:当一个IP网关(源端网关)被用来在IP网络中拨打一个电话时,它从拨号电话接收被呼叫方的电话号码,并将它转化为远端或被呼叫方网关(目的地网关)的IP地址,这可能是在初始网关或中央目录服务器中进行的一次表查询。源端网关中的表查询往往要快得多,将呼叫连接缩短到1或2秒,而中央服务器则需要4或5秒。 2.连接功能:建立源端网关与目的地网关的连接,设置交换呼叫和兼容性信息,并进行任何选项协商和安全握 1. Query function: When an IP gateway (source gateway) is used to make a call in the IP network, it receives the called party’s telephone number from the dial-up telephone and translates it into a remote or called party gateway (Destination gateway) IP address, which may be the initial gateway or central directory server in a table query. Table lookups in source gateways tend to be much faster, reducing call connections to 1 or 2 seconds, while central servers take 4 or 5 seconds. 2. Connection Function: Establish connection between source gateway and destination gateway, set exchange call and compatibility information, and conduct any option negotiation and security hold