Yealink CP860 SERIES, Administrator'S Manual

Page: 1093 / 1126

Appendix
1067
The call cannot be set up successfully.
User A Proxy Server User B
F1. INVITE B
F2. INVITE B
F3. 180 Ringing
F4. 180 Ringing
F8. 200 OK
F7. 200 OK
F5. CANCEL
F6. CANCEL
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. Proxy server forwards
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