Cisco Systems IP phone 7960 manual Pbx B

Appendix B SIP Call Flows

			Call Flow Scenarios for Successful Calls
	Step	Action	Description
13		INVITE—Gateway 1 to	Gateway 1 sends a SIP INVITE request to Gateway 2. In
		Gateway 2	the INVITE request, a unique Call-ID is generated and the
			Requested-By field indicates that User B requested the call.
14		Setup—Gateway 2 to PBX B	Gateway 2 receives the INVITE request from Gateway 1
			and initiates a Call Setup with User C via PBX B.
15		100 Trying—Gateway 2 to	Gateway 2 sends a SIP 100 Trying response to the INVITE
		Gateway 1	request sent by Gateway 1. The 100 Trying response
			indicates that Gateway 2 has received the INVITE request
			but that User C has not yet been located.
16		Call Proceeding—PBX B to	PBX B sends a Call Proceeding message to Gateway 2.
		Gateway 2	User C’s phone begins to ring.
17		Alerting—PBX B to Gateway 2	PBX B sends an Alert message to Gateway 2.
18		180 Ringing—Gateway 2 to	Gateway 2 sends a SIP 180 Ringing response to Gateway 1.
		Gateway 1	The 180 Ringing response indicates that Gateway 2 has
			located, and is trying to alert, User C.
19		Connect—PBX B to Gateway 2	User C answers the phone. PBX B sends a Connect
			message to Gateway 2. The Connect message notifies
			Gateway 2 that the connection has been made.
20		200 OK—Gateway 2 to	Gateway 2 sends a SIP 200 OK response to Gateway 1. The
		Gateway 1	200 OK response notifies Gateway 1 that the connection
			has been made.
			If User C supports the media capability advertised in the
			INVITE message sent by User A, it advertises the
			intersection of its own and User A’s media capability in the
			200 OK response. If User C does not support the media
			capability advertised by User A, it sends back a 400 Bad
			Request response with a 304 Warning header field.
21		Connect ACK—Gateway 2 to	Gateway 2 acknowledges PBX B’s Connect message.
		PBX B
22		ACK—Gateway 1 to Gateway 2	Gateway 1 sends a SIP ACK to Gateway 2. The ACK
			confirms that Gateway 1 has received the 200 OK message
			from Gateway 2.
			Cisco SIP IP Phone 7960 Administrator Guide
	78-10497-02			B-15