Cisco IOS Voice, Video, and Fax Configuration Guide, Release 12.2 - Configuring SIP for VoIP [Cisco

Components of SIP SIP is a peer-to-peer protocol. The peers in a session are called user agents (UAs). A user agent can function in one of the following roles: • User agent client (UAC)—A client application that initiates the SIP request. • User agent ser

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