Yealink SIP-T21 E2 Administrator's Guide

Appendix
1083
Step
Action
Description
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.
F28
BYE—Proxy Server to User B
The proxy server forwards the BYE request
to User B.
F29
200OK—User B to Proxy Server
User B sends a SIP 200 OK response to the

Yealink SIP-T21 E2 Specifications

General

Brand	Yealink
Model	SIP-T21 E2
Category	IP Phone
Language	English