Appendix
799
200OK—Proxy Server to User A
The proxy server forwards the SIP 200 OK
response to User A.
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.
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 SIP IP 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 attended transfer. In this call flow scenario, the end users are User A,
User B, and User C. They are all using Yealink SIP IP 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.
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