Yealink SIP-T2 Series, Administrator'S Manual

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Administrator’s Guide for SIP-T2 Series/T19(P) E2/T4 Series/CP860 IP Phones
968
Step Action Description
User A Ringing response to User A. User A
hears the ring-back tone indicating that
User C is being alerted.
F19
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.
F20
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.
F21 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.
F22 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.
F23
REFER—User A to Proxy
Server
User A sends a REFER message to the
proxy server. User A performs a transfer
of User B to User C.
F24
202 Accepted—Proxy Server
to User A
The proxy server sends a SIP 202
Accepted response to User A. The 202
Accepted response notifies User A that
the proxy server has received the REFER
message.
F25 REFER—Proxy Server to User B
The proxy server forwards the REFER
message to User B.
F26
202 Accepted—User B to
Proxy Server
User B sends a SIP 202 Accept response
to the proxy server. The 202 Accepted
response indicates that User B accepts
the transfer.
F27 BYE—User A to Proxy Server
User A terminates the call session by
sending a SIP BYE request to the proxy
server. The BYE request indicates that
User A wants to release the call.