ZyXEL VMG9823 User Guide - Page 230

SIP Call Progression Through Proxy Servers

Page 230 highlights

Chapter 21 Voice Table 103 SIP Call Progression (continued) A B 6. BYE 7. OK 1 A sends a SIP INVITE request to B. This message is an invitation for B to participate in a SIP telephone call. 2 B sends a response indicating that the telephone is ringing. 3 B sends an OK response after the call is answered. 4 A then sends an ACK message to acknowledge that B has answered the call. 5 Now A and B exchange voice media (talk). 6 After talking, A hangs up and sends a BYE request. 7 B replies with an OK response confirming receipt of the BYE request and the call is terminated. SIP Call Progression Through Proxy Servers Usually, the SIP UAC sets up a phone call by sending a request to the SIP proxy server. Then, the proxy server looks up the destination to which the call should be forwarded (according to the URI requested by the SIP UAC). The request may be forwarded to more than one proxy server before arriving at its destination. The response to the request goes to all the proxy servers through which the request passed, in reverse sequence. Once the session is set up, session traffic is sent between the UAs directly, bypassing all the proxy servers in between. 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 137 SIP Call Through Proxy Servers PROXY 1 SIP PROXY 2 SIP UA 1 SIP & RTP VMG9823-B10A User's Guide 230 SIP UA 2

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Chapter 21 Voice
VMG9823-B10A User’s Guide
230
1
A
sends a SIP INVITE request to
B
. This message is an invitation for
B
to participate in a SIP
telephone call.
2
B
sends a response indicating that the telephone is ringing.
3
B
sends an OK response after the call is answered.
4
A
then sends an ACK message to acknowledge that
B
has answered the call.
5
Now
A
and
B
exchange voice media (talk).
6
After talking,
A
hangs up and sends a BYE request.
7
B
replies with an OK response confirming receipt of the BYE request and the call is terminated.
SIP Call Progression Through Proxy Servers
Usually, the SIP UAC sets up a phone call by sending a request to the SIP proxy server. Then, the
proxy server looks up the destination to which the call should be forwarded (according to the URI
requested by the SIP UAC). The request may be forwarded to more than one proxy server before
arriving at its destination.
The response to the request goes to all the proxy servers through which the request passed, in
reverse sequence. Once the session is set up, session traffic is sent between the UAs directly,
bypassing all the proxy servers in between.
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 137
SIP Call Through Proxy Servers
6. BYE
7. OK
Table 103
SIP Call Progression (continued)
A
B
UA 1
UA 2
PROXY 1
PROXY 2
SIP
SIP
SIP
SIP
&
RTP