Yealink SIP-T2XP Administrator's Manual page 448

Administrator's Guide for SIP-T2xP IP Phones
Step
302 Move Temporarily—Proxy
F7
Server to User A
F8 ACK—User A to Proxy Server
F9 INVITE—User A to Proxy Server
F10 INVITE—Proxy Server to User C
180 Ringing—User C to Proxy
F11
Server
180 Ringing—Proxy Server to
F12
User A
F13 200OK—User C to Proxy Server
F14 200OK—Proxy Server to User A
F15 ACK— User A to Proxy Server
F16 ACK—Proxy Server to User C
432
Action
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 ACK 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
requests the call.
The proxy server forwards 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 User
C is being alerted.
User C sends a SIP 200 OK response to
the proxy server. The 200 OK response
notifies User A that the connection has
been made.
The proxy server forwards the SIP 200 OK
response to User A.
User A sends a SIP ACK to the proxy
server. The ACK confirms that User A has
received the 200 OK response. The call
session is now active.
The proxy server sends the ACK
message to User C.
Description