Cisco 7960G Administrator's Manual page 99

Appendix B SIP Call Flows
Step Action
Setup—PBX A to Gateway 1
1.
INVITE—Gateway 1 to Cisco SIP IP phone
2.
Call Proceeding—Gateway 1 to PBX A
3.
100 Trying—Cisco SIP IP phone to
4.
Gateway 1
5. 180 Ringing—Cisco SIP IP phone to
Gateway 1
6. Alerting—Gateway 1 to PBX A
200 OK—Cisco SIP IP phone to Gateway 1
7.
Connect—Gateway 1 to PBX A
8.
Connect ACK—PBX A to Gateway 1
9.
10. ACK—Gateway 1 to Cisco SIP IP phone
11. BYE—Cisco SIP IP phone to Gateway 1
Disconnect—Gateway 1 to PBX A
12.
13. Release—PBX A to Gateway 1
Description
Call setup is initiated between PBX A and Gateway 1. Setup includes
the standard transactions that take place as User A attempts to call
User B.
Gateway 1 maps the SIP URL phone number to a dial peer. The dial
peer includes the IP address and the port number of the SIP-enabled
entity to contact. Gateway 1 sends a SIP INVITE request to the
address it receives as the dial peer, which, in this scenario, is the IP
phone. In the INVITE request:
The IP address of the phone is inserted in the Request-URI field.
•
PBX A is identified as the call session initiator in the From field.
•
A unique numeric identifier is assigned to the call and is inserted
•
in the Call-ID field.
The transaction number within a single call leg is identified in the
•
CSeq field.
The media capability that User A is ready to receive is specified.
•
The port on which the gateway is prepared to receive the RTP
•
data is specified.
Gateway 1 sends a Call Proceeding message to PBX A to
acknowledge the Call Setup request.
The phone sends a SIP 100 Trying response to Gateway 1. The
response indicates that the INVITE request has been received.
The phone sends a SIP 180 Ringing response to Gateway 1. The
response indicates that the user is being alerted.
Gateway 1 sends an Alert message to User A. The message indicates
that Gateway 1 has received a 180 Ringing response from the phone.
User A hears the ringback tone that indicates that User B is being
alerted.
The phone sends a SIP 200 OK response to Gateway 1. The response
notifies Gateway 1 that the connection has been made.
Gateway 1 sends a Connect message to the PBX A. The message
notifies PBX A that the connection has been made.
PBX A acknowledges Gateway 1's Connect message.
Gateway 1 sends a SIP ACK to the phone. The ACK confirms that
Gateway 1 has received the 200 OK response. The call session is now
active.
User B terminates the call session. The phone sends a SIP BYE
request to Gateway 1. The request indicates that User B wants to
release the call.
Gateway 1 sends a Disconnect message to PBX A.
PBX A sends a Release message to Gateway 1.
Cisco SIP IP Phone Administrator Guide, Release 6.x and 7.x
Call Flow Scenarios for Successful Calls
B-3