Yealink SIP-T2 Series, Руководство администратора

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Appendix
959
Step Action Description
F9
INVITE—User C to Proxy
Server
User C sends a SIP INVITE message to
the proxy server. The INVITE request is
an invitation to User A to participate in
a call session.
In the INVITE request:

The IP address of User A is inserted
in the Request-URI field.

User C 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 C is
ready to receive is specified.

The port on which User A is
prepared to receive the RTP data is
specified.
F10
INVITE—Proxy Server to User
A
The proxy server maps the SIP URI in the
To field to User A. The proxy server
sends the INVITE message to User A.
F11
180 Ringing—User A to Proxy
Server
User A sends a SIP 180 Ringing
response to the proxy server. The 180
Ringing response indicates that the user
is being alerted.
F12
180 Ringing—Proxy Server to
User C
The proxy server forwards the 180
Ringing response to User C. User C
hears the ring-back tone indicating that
User A is being alerted.
F13
INVITE—User A to Proxy
Server
User A sends a mid-call INVITE request
to the proxy server with new SDP
session parameters, which are used to
place the call on hold.
F14
INVITE—Proxy Server to User
B The proxy server forwards the mid-call
INVITE message to User B.
F15
200 OK—User B to Proxy
User B sends a 200 OK to the proxy
server. The 200 OK response indicates