User Manual

Appendix
411
Step
Action
Description
Server
indicates that the user is being alerted.
F20
180 Ringing—Proxy Server to
User A
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
F21
200OK—User C to Proxy Server
User C sends a SIP 200 OK response to the
proxy server. The 200 OK response notifies
the proxy server that the connection has
been made.
F22
200OK—Proxy Server to User A
The proxy server forwards the SIP 200 OK
response to User A.
F23
ACK— User A to Proxy Server
User A sends a SIP ACK to the proxy server.
The ACK confirms that User A has received
the 200 OK response. The call session is
now active.
F24
ACK—Proxy Server to User C
The proxy server forwards the ACK message
to User C. The ACK confirms that User A has
received the 200 OK response. The call
session is now active.
Call Transfer with Consultation
The following figure illustrates a successful call between Yealink Skype for Business phones in
which two parties are in a call and then one of the parties transfers the call to the third party
with consultation. This is called consultative transfer. 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 A calls User C.
4. User C answers the call.
5. User A transfers the call to User C.