User Manual

Yealink Skype for Business HD IP Phones Administrator Guide
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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 is 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.
Successful Call Setup and Call Waiting
The following figure illustrates a successful call between Yealink Skype for Business phones in
which two parties are in a call, one of the participants receives and answers an incoming call
from a third party. In this call flow scenario, the end users are User A, User B, and User C. They
are all using Yealink Skype for Business phones, which are connected via an IP network.
The call flow scenario is as follows:
1. User A calls User B.
2. User B answers the call.
3. User C calls User B.