Yealink T29G

Administrator’s Guide for SIP-T2_Series_T4_Series IP Phones
578
Step
Action
Description
F1
INVITE—User A to Proxy
Server
User A sends an INVITE message to a
proxy server. The INVITE request is an
invitation to User B to participate in a
call session.
In the INVITE request:
 The IP address of User B is
inserted in the Request-URI
field.
 User A is identified as the
call session initiator in the
From field.
 A unique numeric identifier
is assigned to the call and
is inserted in the Call-ID
field.
 The transaction number
within a single call leg is
identified in the CSeq
field.
 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.
F2
INVITE—Proxy Server to User
B
The proxy server maps the SIP URI in the
To field to User B. The proxy server
sends the INVITE message to User B.
F3
180 Ringing—User B to Proxy
Server
User B sends a SIP 180 Ringing response
to the proxy server. The 180 Ringing
response indicates that the user is being
alerted.
F4
180 Ringing—Proxy Server to
User A
The proxy server forwards the 180
Ringing response to User A. User A
hears the ring-back tone indicating that
User B is being alerted.
F5
200 OK—User B to Proxy
Server
User B sends a SIP 200 OK response to
the proxy server. The 200 OK response
notifies the proxy server that the