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Cisco SIP IP Phone 7960 Administrator Guide
78-10497-02
Chapter 1 Product Overview
What is Session Initiation Protocol?
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 server (UAS)—A server application that contacts the user when a
SIP request is received and that returns a response on behalf of the user.
Typically, a SIP end point is capable of functioning as both a UAC and a UAS, but
functions only as one or the other per transaction. Whether the endpoint functions
as a UAC or a UAS depends on the UA that initiated the request.
From an architecture standpoint, the physical components of a SIP network can
also be grouped into two categories: clients and servers. Figure 1-1 illustrates the
architecture of a SIP network.
Note
In addition, the SIP servers can interact with other application
services, such as Lightweght Directory Access Protocol (LDAP)
servers, a database application, or an extensible markup language
(XML) application. These application services provide back-end
services such as directory, authentication, and billing services.