Brocade Virtual ADX Server Load Balancing Guide (Supporting ADX v03.1.00) - Manual (Page 340)

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SIP overview
7
SIP packet flow
Figure 40 demonstrates the basic operation of SIP; location of an endpoint, signal of a desire to
communicate, negotiation of session parameters to establish the session, and tear-down of the
session after completion.
FIGURE 40 SIP packet flow
The example in Figure 40 shows packet exchange between two SIP clients, also known as User
Agent Clients (UACs). In the figure each message is labeled with the letter "F" and a number for
reference. The session established between the two end-clients is facilitated by the SIP proxy
server. User1 "calls" User2 using a SIP identity, a type of Uniform Resource Identifier (URI) called a
SIP URI. The SIP URI is similar to an e-mail address, typically containing a username and a host
name. In this case, it is sip:[email protected], where brocade.com is the domain of User1's SIP
service provider.