Yealink SIP-T21 E2

Appendix
1075
Step
Action
Description
INVITE was successfully processed.
F16
200 OK—Proxy Server to User A
The proxy server forwards the 200 OK
response to User A. The 200 OK response
notifies User B is successfully placed on
hold.
F17
ACK—User A to Proxy Server
User A sends an ACK message to the
proxy server. The ACK confirms that User
A has received the 200 OK response. The
call session is now temporarily inactive.
No RTP packets are being sent.
F18
ACK—Proxy Server to User B
The proxy server sends the ACK message
to User B. The ACK confirms that the
proxy server has received the 200 OK
response.
F19
200 OK—User A to Proxy Server
User A sends a 200 OK response to the
proxy server. The 200 OK response
notifies that the connection has been
made.
F20
200 OK—Proxy Server User C
The proxy server forwards the 200 OK
message to User C.
F21
ACK—User C to Proxy Server
User C sends a SIP ACK to the proxy
server. The ACK confirms that User C has
received the 200 OK response. The call
session is now active.
F22
ACK—Proxy Server to User A
The proxy server forwards the SIP ACK to
User A to confirm that User C has received
the 200 OK response.
Call Transfer without 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 a third party without
consultation. This is called a blind 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.