Cisco 7960 Administrator's Manual page 121

Sip ip phone
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Appendix B
SIP Call Flows
Step
Action
1
Setup—PBX A to Gateway 1
2
INVITE—Gateway 1 to Cisco
SIP IP phone
3
Call Proceeding—Gateway 1 to
PBX A
4
100 Trying—Cisco SIP IP phone
to Gateway 1
5
180 Ringing—Cisco SIP IP
phone to Gateway 1
78-10497-02
Description
Call Setup is initiated between PBX A and Gateway 1. The
Call 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 Cisco SIP IP phone.
In the INVITE request:
The IP address of the Cisco SIP IP 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 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 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.
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.
Cisco SIP IP Phone 7960 Administrator Guide
Call Flow Scenarios for Successful Calls
B-13

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