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C-17
Cisco IP Phone Models 7905G and 7912G Administrator Guide (SIP)
OL-4277-01
Appendix C SIP Call Flows
Call Flow Scenarios for Successful Calls
Table C-7 Action Descriptions
Step Action Description
Step 1
INVITE—Cisco IP Phone A to SIP server Cisco IP Phone A sends a call session
INVITE request to the SIP server to pass on to
Cisco IP Phone B.
Step 2
100 Trying—SIP server to Cisco IP Phone A SIP server returns a 100 Trying message,
indicating that the INVITE request has been
received.
Step 3
407 Proxy Authentication Required— SIP
server to Cisco IP Phone A
SIP server returns a request for authentication
to Cisco IP Phone A.
Step 4
ACK—Cisco IP Phone A to SIP server Cisco IP Phone A acknowledges the request
for authentication.
Step 5
INVITE—Cisco IP Phone A to SIP server Cisco IP Phone A sends a call session
INVITE request along with authentication
credential to the SIP server to pass on to
Cisco IP Phone B.
Step 6
100 Trying—SIP server to Cisco IP Phone A SIP server returns a 100 Trying message,
indicating that the INVITE request has been
received.
Step 7
INVITE—SIP server to Cisco IP Phone B SIP server sends the call session INVITE
request to Cisco IP Phone B.
Step 8
100 Trying—Cisco IP Phone B to SIP server Cisco IP Phone B returns a 100 trying
message indicating that the INVITE request
has been received.
Step 9
180 Ringing—Cisco IP Phone B to SIP server Cisco IP Phone B sends a 180 ringing
response to the SIP server to pass on to
Cisco IP Phone A.
Step 10
180 Ringing—SIP server to Cisco IP Phone A SIP server sends the 180 ringing response to
Cisco IP Phone A.
Step 11
200 OK—Cisco IP Phone B to SIP server Cisco IP Phone B sends a 200 OK message to
the SIP server indicating that a connection has
been established.
Step 12
200 OK—SIP server to Cisco IP Phone A SIP server passes the 200 OK message to
Cisco IP Phone A.