User Manual

Yealink Skype for Business HD IP Phones Administrator Guide
414
Step
Action
Description
now active.
F8
ACK—Proxy Server to User B
The proxy server sends the SIP ACK to User
B. The ACK confirms that the proxy server
has received the 200 OK response. The call
session is now active.
F9
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.
F10
INVITE—Proxy Server to User B
The proxy server forwards the mid-call
INVITE message to User B.
F11
200 OK—User B to Proxy Server
User B sends a SIP 200 OK response to the
proxy server. The 200 OK response notifies
User A that the INVITE was successfully
processed.
F12
200 OK—Proxy Server to User A
The proxy server forwards the 200 OK
response to User A. The 200 OK response
notifies User B is successfully placed on
hold.
F13
ACK—User A to Proxy Server
User A sends an 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.
F14
ACK—Proxy Server to User B
The proxy server sends the ACK message to
User B. The ACK confirms that the proxy
server has received the 200 OK response.
F15
INVITE—User A to Proxy Server
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.
F16
INVITE—Proxy Server to User C
The proxy server maps the SIP URI in the To
field to User C. The proxy server sends the
INVITE request to User C.
F17
180 Ringing—User C to Proxy
Server
User C sends a SIP 180 Ringing response to
the proxy server. The 180 Ringing response
indicates that the user is being alerted.