Yealink T46G Administrator's Manual page 417

Step Action
F10 INVITE—Proxy Server to User B
F11 200 OK—User B to Proxy Server
F12 200 OK—Proxy Server to User A
F13 ACK—User A to Proxy Server
F14 ACK—Proxy Server to User B
F15 INVITE—User A to Proxy Server
F16 INVITE—Proxy Server to User C
180 Ringing—User C to Proxy
F17
Server
180 Ringing—Proxy Server to
F18
User A
F19 200OK—User C to Proxy Server
F20 200OK—Proxy Server to User A
Description
The proxy server forwards the mid-call
INVITE message to User B.
User B sends a SIP 200 OK response to the
proxy server. The 200 OK response notifies
User A that the INVITE is successfully
processed.
The proxy server forwards the 200 OK
response to User A. The 200 OK response
notifies User A that User B is successfully
placed on hold.
User A sends the ACK message to the proxy
server. The ACK confirms that User A has
received the 200 OK response. The call
session is now temporarily inactive. No RTP
packets are being sent.
The proxy server sends the ACK message to
User B. The ACK confirms that the proxy
server has received the 200 OK response.
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 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 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. The 200 OK response
Appendix
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