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Cisco SIP IP Phone 7960 Administrator Guide
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AppendixB SIP Call Flows Call Flow Scenarios for Successful Calls
Step Action Description
1Setup—PBX A to Gateway 1 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.
2INVITE—Gateway 1 to Cisco
SIP IP phone Gateway 1 maps the SIP URL phone number to a dial-peer.
The dial-peer includes the IP address and the p ort num be r
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.
3Call Proceeding—Gateway 1 to
PBX A Gateway 1 sends a Call Proceeding message to PBX A to
acknowledge the Call Setup request.
4100 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.
5180 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.