Chapter 16 VoIP
Management Switch Card User’s Guide
602
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 407 SIP Call Through Proxy Servers
The following table shows the SIP call progression.
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.
Table 325 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
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