Chapter 21 Voice
VMG8924-B10A User’s Guide
255
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 154 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.
3 Proxy 2 sends a SIP INVITE request to User Agent 2.
4 User Agent 2 sends a response back to Proxy 2 indicating that the phone is ringing. The response
is relayed back to User Agent 1 via Proxy 1.
Table 120 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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