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)。

youdao

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。

youdao