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B-43
Cisco Unified IP Phone 7960G and 7940G Administration Guide for Release 8.0 (SIP)
OL-7890-01
Appendix B SIP Call Flows
Call Flow Scenarios for Successful Calls
Call from a Cisco SIP IP Phone to a Cisco SIP IP Phone Using a SIP Backup Proxy
Figure B-16
illustrates a successful call from a Cisco SIP IP phone to a Cisco SIP IP phone that uses a SIP
backup proxy.
5.
INVITE—Cisco SIP IP phone to
primary proxy (fifth try)
The phone retries a fifth time to connect to the proxy by sending out the
INVITE message.
6.
INVITE—Cisco SIP IP phone to
primary proxy (sixth try)
The phone retries a sixth time to connect to the proxy by sending out the
INVITE message.
7.
INVITE—Cisco SIP IP phone to
primary proxy (seventh try)
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.
8.
INVITE—Cisco SIP IP phone to the
gateway (backup proxy)
The phone tries to connect to the gateway (backup proxy) by sending out the
INVITE message.
9.
Setup—Gateway to the PBX
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.
10.
Call Proceeding—PBX to the gateway The PBX sends a Call Proceeding message to the gateway to acknowledge
the Call Setup request.
11.
100 Trying—Gateway to Cisco SIP IP
phone (A)
The gateway sends a SIP 100 Trying response to A. The response indicates
that the INVITE request has been received.
12.
Alerting—PBX to the gateway
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.
13.
180 Ringing—Gateway to Cisco SIP
IP phone (A)
The gateway sends a SIP 180 Ringing response to A. The response indicates
that the gateway is being alerted.
14.
Connect—PBX to the gateway
The PBX sends a Connect message to the gateway. The message notifies the
gateway that the connection has been made.
15.
200 OK—Gateway to Cisco SIP IP
phone (A)
The gateway sends a SIP 200 OK response to A. The response notifies A that
the connection has been made.
16.
ACK—Cisco SIP IP phone (A) to the
gateway
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.
17.
Connect ACK—Gateway to the PBX
The gateway acknowledges PBX Connect message.
18.
BYE—Cisco SIP IP phone
(A) to the gateway
A terminates the call session and sends a SIP BYE request to the gateway.
The request indicates that A wants to release the call.
19.
Disconnect—Gateway to the PBX
The gateway sends a Disconnect message to the PBX.
20.
Release—PBX to the gateway
The PBX sends a Release message to the gateway.
21.
200 OK—Gateway to Cisco SIP IP
phone (A)
The gateway sends a SIP 200 OK response to A. The response notifies A that
the gateway has received the BYE request.
22.
Release Complete—Gateway to the
PBX
The gateway sends a Release Complete message to the PBX, and the call
session terminates.
Step
Action
Description