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D-7
Cisco ATA 186 and Cisco ATA 188 Analog Telephone Adaptor Administrator’s Guide (SIP)
OL-3410-01
Appendix D SIP Call Flows
Call Flow Scenarios for Successful Calls
Table D-5 Action Descriptions
Step Action Description
Step 1
INVITE—Cisco ATA A to SIP server Cisco ATA A sends a call session INVITE request to the SIP
server to pass on to Cisco ATA B.
Step 2
100 Trying—SIP server to Cisco ATA A SIP server returns a 100 trying message, indicating that the
INVITE request has been received.
Step 3
INVITE—SIP server to Cisco ATA B SIP server sends the call session INVITE request to Cisco ATA B.
Step 4
100 Trying—Cisco ATA B to SIP server Cisco ATA B returns a 100 trying message indicating that the
INVITE request has been received.
Step 5
180 Ringing—Cisco ATA B to SIP server Cisco ATA B sends a 180 ringing response to the SIP server to
pass on to Cisco ATA A.
Step 6
180 Ringing—SIP server to Cisco ATA A SIP server sends the 180 ringing response to Cisco ATA A.
Step 7
200 OK—Cisco ATA B to SIP server Cisco ATA B sends a 200 OK message to the SIP server
indicating that a connection has been established.
Step 8
200 OK—SIP server to Cisco ATA A SIP server passes the 200 OK message to Cisco ATA A.
Step 9
ACK—Cisco ATA A to SIP server Cisco ATA A sends acknowledgement of the 200 OK response to
the SIP server to pass on to Cisco ATA B.
Step 10
ACK—SIP server to Cisco ATA B SIP server passes ACK response to Cisco ATA B.
A two-way voice path is established between Cisco ATA A and Cisco ATA B.
Step 11
BYE—Cisco ATA A to SIP server Cisco ATA A terminates the call session and sends a BYE request
to the SIP server indicating that Cisco ATA A wants to terminate
the call.
Step 12
100 Trying—SIP server to Cisco ATA A SIP server returns a 100 trying message indicating that the BYE
request has been received.
Step 13
BYE—SIP server to Cisco ATA B SIP server passes the BYE request to Cisco ATA B.
Step 14
200 OK—Cisco ATA B to SIP server Cisco ATA B sends a 200 OK message to the SIP server
indicating that Cisco ATA B has received the BYE request.
Step 15
200 OK—SIP server to Cisco ATA A SIP server passes the BYE request to Cisco ATA A.