Administrator’s Guide for SIP-T5 Series Smart Media Phones
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indicates that the user is being alerted.
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.
200OK—User C to Proxy Server
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.
200OK—Proxy Server to User A
The proxy server forwards the SIP 200 OK
response to User A. The 200 OK response
notifies User A that the connection has
been made.
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 the proxy
server has received the 200 OK response.
The call session is now active.
Busy Call Forward
The following figure illustrates successful call forwarding between Yealink SIP IP phones in which
User B has enabled busy call forward. The incoming call is forwarded to User C when User B is
busy. 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 B enables busy call forward, and the destination number is User C.
2. User A calls User B.
3. User B is busy.
4. User B forwards the incoming call to User C.
5. User C answers the call.
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