Cisco Systems IP phone 7960 manual 78-10497-02

Appendix B SIP Call Flows

Call Flow Scenarios for Failed Calls

Step Action Description

1INVITE—Cisco SIP IP phone A Cisco SIP IP phone A sends a SIP INVITE request to the

	to SIP proxy server	SIP proxy server. The INVITE request is an invitation to
		User B to participate in a call session.
		In the INVITE request:
		• The phone number of User B is inserted in the
		Request-URI field in the form of a SIP URL. The SIP
		URL identifies the address of User B and takes a form
		similar to an email address (user@host where user is
		the telephone number and host is either a domain name
		or a numeric network address). For example, the
		Request-URI field in the INVITE request to User B
		appears as “INVITE sip:555-0002@companyb.com;
		user=phone.” The “user=phone” parameter
		distinquishes that the Request-URI address is a
		telephone number rather than a user name.
		• Cisco SIP IP phone 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.
2	407 Authentication Error—SIP	SIP proxy server sends a SIP 407 Authentication Error
	proxy server to Cisco SIP IP	response to Cisco SIP IP phone A.
	phone A
3	ACK—Cisco SIP IP phone A to	Cisco SIP IP phone A sends a SIP ACK to the SIP proxy
	SIP proxy server	server acknowledging the 407 error message.
4	Resend INVITE—Cisco SIP IP	Cisco SIP IP phone A resends a SIP INVITE to the SIP
	phone A to SIP proxy server	proxy server with authentication credentials.

	Cisco SIP IP Phone 7960 Administrator Guide
78-10497-02		B-71