Cisco Systems IP phone 7960 manual Call Flow Scenarios for Failed Calls

Appendix B SIP Call Flows

			Call Flow Scenarios for Failed 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.
6		Alerting—Gateway 1 to PBX A	Gateway 1 sends an Alert message to PBX A.
			Cisco SIP IP Phone 7960 Administrator Guide
	78-10497-02			B-61