Cisco Systems IP phone 7960 manual Step Action

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 Cisco

	to Cisco SIP IP phone B	SIP IP phone B. 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	486 Busy Here—Cisco SIP IP	Cisco SIP IP phone B sends a 486 Busy here message to the
	phone B to Cisco SIP IP phone A Cisco SIP IP phone A. The message indicates that Cisco
		SIP IP phone B is in use and the user is not willing or able
		to take additional calls.
3	ACK—Cisco SIP IP phone A to	Cisco SIP IP phone A sends a SIP ACK to the Cisco SIP IP
	Cisco SIP IP phone B	phone B. The ACK confirms that Cisco SIP IP phone A has
		received the 486 Busy here response from Cisco SIP IP
		phone B.

	Cisco SIP IP Phone 7960 Administrator Guide
78-10497-02		B-67