ZyXEL Communications VMG5313-BXB SERIES User Manual page 239

Figure 141 SIP Call Through Proxy Servers
SIP
UA 1
The following table shows the SIP call progression.
Table 109 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.
User Agent 2 sends an OK response to Proxy 2 after the call is answered. This is also relayed
5
back to User Agent 1 via Proxy 1.
Chapter 22 Voice
PROXY 1
SIP
SIP &
PROXY 1
Invite
100 Trying
180 Ringing
200 OK
VMG5313-BXB Series User's Guide
239
PROXY 2
RTP
PROXY 2
Invite
100 Trying
180 Ringing
200 OK
SIP
UA 2
UA 2
180 Ringing
200 OK
RTP
BYE