| 摘要 |
A SIP client for a communication device includes a user agent to communicate with a user application in the communication device. The user agent provides a high-level application interface to the user application and translates user commands into corresponding signaling and media operations. The same user agent may be shared by a plurality of user applications. A signaling agent controlled by the user agent performs signaling operations necessary to establish and maintain communication sessions. To avoid signaling overhead on a high cost network, the SIP client can be located in a remote network so signaling messages do not need to traverse the high cost network.
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