B-4
Cisco SIP IP Phone Administrator Guide
Appendix B SIP Call Flows
Call Flow Scenarios for Successful Calls
Gateway-to-Cisco SIP IP Phone—Successful Call Setup and Call Hold
Figure B-2
illustrates a successful gateway-to-Cisco SIP IP phone call setup and call hold. In this
scenario, the two end users are User A and User B. User A is located at PBX A. PBX A is connected to
Gateway 1 (SIP Gateway) via a T1/E1. User B is located at a Cisco SIP IP phone. Gateway 1 is connected
to the Cisco SIP IP phone over an IP network.
The call flow is as follows:
1.
User A calls User B.
2.
User B answers the call.
3.
User B puts User A on hold.
4.
User B takes User A off hold.
4.
100 Trying—Cisco SIP IP phone
to Gateway 1
The Cisco SIP IP phone sends a SIP 100 Trying response to Gateway 1. The
100 Trying response indicates that the INVITE request has been received by the
Cisco SIP IP phone.
5.
180 Ringing—Cisco SIP IP
phone to Gateway 1
The Cisco SIP IP phone sends a SIP 180 Ringing response to Gateway 1. The
180 Ringing response indicates that the user is being alerted.
6.
Alerting—Gateway 1 to PBX A
Gateway 1 sends an Alert message to User A. The Alert message indicates that
Gateway 1 has received a 180 Ringing response from the Cisco SIP IP phone. User
A hears the ringback tone that indicates that User B is being alerted.
7.
200 OK—Cisco SIP IP phone to
Gateway 1
The Cisco SIP IP phone sends a SIP 200 OK response to Gateway 1. The 200 OK
response notifies Gateway 1 that the connection has been made.
8.
Connect—Gateway 1 to PBX A
Gateway 1 sends a Connect message to PBX A. The Connect message notifies
PBX A that the connection has been made.
9.
Connect ACK—PBX A to
Gateway 1
PBX A acknowledges Gateway 1’s Connect message.
10.
ACK—Gateway 1 to Cisco SIP
IP phone
Gateway 1 sends a SIP ACK to the Cisco SIP IP phone. The ACK confirms that
Gateway 1 has received the 200 OK response. The call session is now active.
11.
BYE—Cisco SIP IP phone to
Gateway 1
User B terminates the call session at his Cisco SIP IP phone and the phone sends
a SIP BYE request to Gateway 1. The BYE request indicates that User B wants to
release the call.
12.
Disconnect—Gateway 1 to
PBX A
Gateway 1 sends a Disconnect message to PBX A.
13.
Release—PBX A to Gateway 1
PBX A sends a Release message to Gateway 1.
14.
200 OK—Gateway 1 to
Cisco SIP IP phone
Gateway 1 sends a SIP 200 OK response to the Cisco SIP IP phone. The 200 OK
response notifies the phone that Gateway 1 has received the BYE request.
15.
Release Complete—Gateway 1
to PBX A
Gateway 1 sends a Release Complete message to PBX A and the call session is
terminated.
Step
Action
Description