Cisco 7960G Administrator's Manual page 139

Appendix B SIP Call Flows
Step Action
INVITE—Cisco SIP IP phone to
1.
primary proxy
INVITE—Cisco SIP IP phone to
2.
primary proxy (second try)
INVITE—Cisco SIP IP phone to
3.
primary proxy (third try)
INVITE—Cisco SIP IP phone to
4.
primary proxy (fourth try)
INVITE—Cisco SIP IP phone to
5.
primary proxy (fifth try)
INVITE—Cisco SIP IP phone to
6.
primary proxy (sixth try)
7. INVITE—Cisco SIP IP phone to
primary proxy (seventh try)
INVITE—Cisco SIP IP phone to the
8.
gateway (backup proxy)
Setup—Gateway to the PBX
9.
Call Proceeding—PBX to the gateway The PBX sends a Call Proceeding message to the gateway to acknowledge
10.
11. 100 Trying—Gateway to Cisco SIP IP
phone (A)
12. Alerting—PBX to the gateway
13. 180 Ringing—Gateway to Cisco SIP
IP phone (A)
14. Connect—PBX to the gateway
200 OK—Gateway to Cisco SIP IP
15.
phone (A)
ACK—Cisco SIP IP phone (A) to the
16.
gateway
Connect ACK—Gateway to the PBX
17.
BYE—Cisco SIP IP phone
18.
(A) to the gateway
Disconnect—Gateway to the PBX
19.
Release—PBX to the gateway
20.
200 OK—Gateway to Cisco SIP IP
21.
phone (A)
Release Complete—Gateway to the
22.
PBX
Description
The phone tries to connect to the proxy by sending out the INVITE message.
The phone retries a second time to connect to the proxy by sending out the
INVITE message.
The phone retries a third time to connect to the proxy by sending out the
INVITE message.
The phone retries a fourth time to connect to the proxy by sending out the
INVITE message.
The phone retries a fifth time to connect to the proxy by sending out the
INVITE message.
The phone retries a sixth time to connect to the proxy by sending out the
INVITE message.
The phone retries a seventh time to connect to the proxy. If the connection is
not successful after this trial, the "Network Delay, Trying Backup" message
displays on the phone.
The phone tries to connect to the gateway (backup proxy) by sending out the
INVITE message.
Call setup is initiated between the gateway and the PBX. The setup includes
the standard transactions that take place as A attempts to call B.
the Call Setup request.
The gateway sends a SIP 100 Trying response to A. The response indicates
that the INVITE request has been received.
The PBX sends an Alert message to the gateway. The message indicates that
the PBX has received a 100 Trying Ringing response from the gateway.
The gateway sends a SIP 180 Ringing response to A. The response indicates
that the gateway is being alerted.
The PBX sends a Connect message to the gateway. The message notifies the
gateway that the connection has been made.
The gateway sends a SIP 200 OK response to A. The response notifies A that
the connection has been made.
A sends a SIP ACK to the gateway. The ACK confirms that A has received
the 200 OK response. The call session is now active.
The gateway acknowledges PBX Connect message.
A terminates the call session and sends a SIP BYE request to the gateway.
The request indicates that A wants to release the call.
The gateway sends a Disconnect message to the PBX.
The PBX sends a Release message to the gateway.
The gateway sends a SIP 200 OK response to A. The response notifies A that
the gateway has received the BYE request.
The gateway sends a Release Complete message to the PBX, and the call
session terminates.
Cisco SIP IP Phone Administrator Guide, Release 6.x and 7.x
Call Flow Scenarios for Successful Calls
B-43