ZyXEL Communications VMG892-B10A User Manual page 257

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
SIP
UA 1
The following table shows the SIP call progression.
Table 120 SIP Call Progression
UA 1
Invite
ACK
RTP
200 OK
User Agent 1 sends a SIP INVITE request to Proxy 1. This message is an invitation to User
1
Agent 2 to participate in a SIP telephone call. Proxy 1 sends a response indicating that it is trying
to complete the request.
Proxy 1 sends a SIP INVITE request to Proxy 2. Proxy 2 sends a response indicating that it is
2
trying to complete the request.
Proxy 2 sends a SIP INVITE request to User Agent 2.
3
User Agent 2 sends a response back to Proxy 2 indicating that the phone is ringing. The response
4
is relayed back to User Agent 1 via Proxy 1.
VMG8924-B10A and VMG8924-B30A Series User's Guide
PROXY 1
SIP
SIP & RTP
PROXY 1
Invite
100 Trying
180 Ringing
200 OK
PROXY 2
SIP
UA 2
PROXY 2
Invite
100 Trying
180 Ringing
200 OK
Chapter 21 Voice
UA 2
180 Ringing
200 OK
RTP
BYE
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