Yealink SIP-T2XP Administrator's Manual page 575

Step Action
INVITE—Proxy Server to User
F2
B
302 Move Temporarily—User
F3
B to Proxy Server
F4 ACK—Proxy Server to User B
302 Move Temporarily—Proxy
F5
Server to User A
F6 ACK—User A to Proxy Server
INVITE—User A to Proxy
F7
Server
INVITE—Proxy Server to User
F8
C
180 Ringing—User C to Proxy
F9
Server
180 Ringing—Proxy Server to
F10
User A
Description
The media capability User A is

ready to receive is specified.
The port on which User B is

prepared to receive the RTP data is
specified.
The proxy server maps the SIP URI in the
To field to User B. The proxy server
sends the INVITE message to User B.
User B sends a SIP 302 Moved
Temporarily message to the proxy
server. The message indicates that User
B is not available at SIP phone B. User B
rewrites the contact-URI.
The proxy server sends a SIP ACK to
User B, the ACK message notifies User B
that the proxy server has received the
302 Move Temporarily message.
The proxy server forwards the 302
Moved Temporarily message to User A.
User A sends a SIP ACK to the proxy
server. The ACK message notifies the
proxy server that User A has received
the 302 Move Temporarily message.
User A sends a SIP INVITE request to the
proxy server. In the INVITE request, a
unique Call-ID is generated and the
Contact-URI field indicates that User A
requested the call.
The proxy server maps the SIP URI in the
To field to User C. The proxy server
sends the SIP INVITE request to User C.
User C sends a SIP 180 Ringing
response to the proxy server. The 180
Ringing response indicates that the user
is being alerted.
The proxy server forwards the 180
Ringing response to User A. User A
hears the ring-back tone indicating that
Appendix
557