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Chapter 18 VoIP
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 374 SIP Call Through Proxy Servers
UA 1
The following table shows the SIP call progression.
Table 287 SIP Call Progression
UA 1
Invite
ACK
RTP
200 OK
1 User Agent 1 sends a SIP INVITE request to Proxy 1. This message is an invitation to
User Agent 2 to participate in a SIP telephone call. Proxy 1 sends a response indicating
that it is trying to complete the request.
2 Proxy 1 sends a SIP INVITE request to Proxy 2. Proxy 2 sends a response indicating
that it is trying to complete the request.
542
PROXY 1
SIP
PROXY 1
Invite
100 Trying
180 Ringing
200 OK
PROXY 2
SIP
SIP
&
RTP
PROXY 2
Invite
100 Trying
180 Ringing
200 OK
MSC1000G/1024G/1224G Series User's Guide
SIP
UA 2
UA 2
180 Ringing
200 OK
RTP
BYE
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Troubleshooting
