Yealink SIP-T19 E2 T4 Series, Administrator'S Manual

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Administrator’s Guide for SIP-T2 Series/T19(P) E2/T4 Series/T5 Series IP Phones
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Step Action Description
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.