Figure 100 Sip Call Through Proxy Servers; Table 59 Sip Call Progression - ZyXEL Communications P-2602HWLNI User Manual

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

UA 1
The following table shows the SIP call progression.

Table 59 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.
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.
174
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
SIP
UA 2
UA 2
180 Ringing
200 OK
RTP
BYE
P-2602HWLNI User's Guide