Cisco Systems IP phone 7960 manual Step Action Description, PBX a

Appendix B SIP Call Flows

Call Flow Scenarios for Successful Calls

Step	Action	Description
1	Setup—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.
2	INVITE—Gateway 1 to Cisco	Gateway 1 maps the SIP URL phone number to a dial-peer.
	SIP IP phone	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.
3	Call Proceeding—Gateway 1 to	Gateway 1 sends a Call Proceeding message to PBX A to
	PBX A	acknowledge the Call Setup request.
4	100 Trying—Cisco SIP IP phone	The Cisco SIP IP phone sends a SIP 100 Trying response
	to Gateway 1	to Gateway 1. The 100 Trying response indicates that the
		INVITE request has been received by the Cisco SIP IP
		phone.
5	180 Ringing—Cisco SIP IP	The Cisco SIP IP phone sends a SIP 180 Ringing response
	phone to Gateway 1	to Gateway 1. The 180 Ringing response indicates that the
		user is being alerted.

	Cisco SIP IP Phone 7960 Administrator Guide
78-10497-02		B-5