Unlike a proxy that forwards on the requests, a B2BUA acts as both a user agent server (UAS) and a user agent client (UAC) to further participate in the SIP transaction.

与转发请求的代理不同，B2BUA 同时充当进一步参与 SIP 事务的用户代理服务器 (UAS) 和用户代理客户机 (UAC)。

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A user agent client (UAC) is formally defined in SIP as an endpoint that can create and manage SIP sessions.

用户代理客户机(user Agent Client, UAC)在SIP中被正式定义为能创建和管理SIP会话的端点。

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A third option, rather than using client side XSLT, is to detect the user agent at the server and to provide different content depending on the user agent's capabilities.

除了使用客户端XSLT之外，还有第三种选择，那就是在服务器检测用户代理，并根据用户代理的功能提供不同的内容。

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