3Com MSR 50 Series Configuration Manual page 2372

2372 C 137: SIP O
HAPTER VERVIEW
Figure 688 illustrates the complete call setup procedures.
Figure 688 Call setup procedures involving a proxy server
Originating side
This is a simplified scenario where only one proxy server is involved and no
registrar is present. A complex scenario, however, may involve multiple proxy
servers and registrars.
Call redirection
When a SIP redirect server receives a session request, it sends back a response
indicating the address of the called SIP endpoint instead of forwarding the
request. The calling and called endpoints thus can send request and response to
each other bypassing the SIP proxy server. See
Proxy server
Invite
100 Trying
180 Ringing
200 OK
RTP/RTCP
BYE
200 for BYE
Terminating side
Invite
100 Trying
180 Ringing
200 OK
ACK for 200
BYE
200 for BYE
Figure 689.