Cisco Systems IP phone 7960 manual Step Action Description

Appendix B SIP Call Flows

Call Flow Scenarios for Successful Calls

Step	Action	Description
3	200 OK—Cisco SIP IP phone B	Cisco SIP IP phone B sends a SIP 200 OK response to
	to Cisco SIP IP phone A	Cisco SIP IP phone A. The 200 OK response notifies Cisco
		SIP IP phone A that the connection has been made.
		If Cisco SIP IP phone B supports the media capability
		advertised in the INVITE message sent by Cisco SIP IP
		phone A, it advertises the intersection of its own and Cisco
		SIP IP phone A’s media capability in the 200 OK response.
		If Cisco SIP IP phone B does not support the media
		capability advertised by Cisco SIP IP phone A, it sends
		back a 400 Bad Request response with a 304 Warning
		header field.
4	ACK—Cisco SIP IP phone A to	Cisco SIP IP phone A sends a SIP ACK to Cisco SIP IP
	Cisco SIP IP phone B	phone B. The ACK confirms that Cisco SIP IP phone A has
		received the 200 OK response from Cisco SIP IP phone B.
		The ACK might contain a message body with the final
		session description to be used by Cisco SIP IP phone B. If
		the message body of the ACK is empty, Cisco SIP IP phone
		B uses the session description in the INVITE request.

A two-way RTP channel is established between Cisco SIP IP phone A and Cisco SIP IP phone B. User B then selects the option to transfer the call to User C.

5		INVITE—Cisco SIP IP phone B		Cisco SIP IP phone B sends a mid-call INVITE to Cisco
		to Cisco SIP IP phone A		SIP IP phone A with new SDP session parameters (IP
				address), which are used to place the call on hold.
				Call_ID=1
				SDP: c=IN IP4 0.0.0.0
6		200 OK—Cisco SIP IP phone A		Cisco SIP IP phone A sends a SIP 200 OK response to
		to Cisco SIP IP phone B		Cisco SIP IP phone B.
7		ACK—Cisco SIP IP phone B to		Cisco SIP IP phone B sends a SIP ACK to Cisco SIP IP
		Cisco SIP IP phone A		phone A. The ACK confirms that Cisco SIP IP phone B has
				received the 200 OK response from Cisco SIP IP phone A.
The RTP channel between Cisco SIP IP phone A and Cisco SIP IP phone B is torn down.
8		INVITE—Cisco SIP IP phone B		Cisco SIP IP phone B sends a SIP INVITE request to Cisco
		to Cisco SIP IP phone C		SIP IP phone C. The INVITE request is an invitation to
				User C to participate in a call session.
			Cisco SIP IP Phone 7960 Administrator Guide
	B-38			78-10497-02