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Chapter 9 Voice
P-2812HNU-51c User’s Guide
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The response to the request goes to all the proxy servers through which the
request passed, in reverse sequence. Once the session is set up, session traffic is
sent between the UAs directly, bypassing all the proxy servers in between.
The following figure shows the SIP and session traffic flow between the user
agents (UA 1 and UA 2) and the proxy servers (this example shows two proxy
servers, PROXY 1 and PROXY 2).
Figure 99 SIP Call Through Proxy Servers
The following table shows the SIP call progression.
Table 65 SIP Call Progression
UA 1 PROXY 1 PROXY 2 UA 2
Invite
Invite
100 Trying Invite
100 Trying
180
Ringing
180
Ringing
180
Ringing
200 OK
200 OK
200 OK
ACK
RTP RTP
BYE
200 OK
UA 1
UA 2
PROXY 1
PROXY 2
SIP
SIP
SIP
SIP & RTP