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
F11 200 OK—User B to Proxy Server
User B sends a SIP 200 OK response to the
proxy server. The 200 OK response notifies
User A that the INVITE is successfully
processed.
F12 200 OK—Proxy Server to User A
The proxy server forwards the 200 OK
response to User A. The 200 OK response
notifies User A that User B is successfully
placed on hold.
F13 ACK—User A to Proxy Server
User A sends the 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.
F14 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.
F15 INVITE—User A to Proxy Server
User A sends a SIP INVITE request to the
proxy server. In the INVITE request, a
unique Call-ID is generated and the
Contact-URI field indicates that User A
requests the call.
F16 INVITE—Proxy Server to User C
The proxy server maps the SIP URI in the To
field to User C. The proxy server sends the
SIP INVITE request to User C.
F17
180 Ringing—User C to Proxy
Server
User C sends a SIP 180 Ringing response to
the proxy server. The 180 Ringing response
indicates that the user is being alerted.
F18
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.
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.