Chapter 11 Voice
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 100 SIP Call Through Proxy Servers
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The following table shows the SIP call progression.
Table 59 SIP Call Progression
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Invite |
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| 100 Trying |
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| 100 Trying |
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180 Ringing
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| 200 OK |
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ACK |
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200 OK |
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| BYE |
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1User 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.
2Proxy 1 sends a SIP INVITE request to Proxy 2. Proxy 2 sends a response indicating that it is trying to complete the request.
3Proxy 2 sends a SIP INVITE request to User Agent 2.
4User 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.
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