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Microsoft Lync Edition Administrator’s Guide for SIP-T2_Series and T4_Series IP Phones
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Step Action Description
that the proxy server has received the
ACK message.
F7
302 Move Temporarily—Proxy
Server to User A The proxy server forwards the 302
Moved Temporarily message to User A.
F8 ACK—User A to Proxy Server
User A sends a SIP ACK to the proxy
server. The ACK message notifies the
proxy server that User A has received
the ACK message.
F9
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.
F10
INVITE—Proxy Server to User
C The proxy server forwards the SIP
INVITE request to User C.
F11
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.
F12
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.
F13
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.
F14
200OK—Proxy Server to User
A The proxy server forwards the SIP 200
OK response to User A.
F15 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.
F16 ACK—Proxy Server to User C
The proxy server sends the ACK
message to User C.