3600 Event: XXX Contact: sip:user@handbook.com Content-Length: 0 M8: The notifier for notify@handbook.com processes the subscription request. A 200 (OK) response is sent to confirm the subscription. SIP/2.0 200 OK Via: SIP/2.0/UDP example.com;branch=z9hG4bKnashds7; received=168.0.2 To: <sip:notify@handbook.com>;tag=abcd1234 From: sip:subscribe@handbook.com>;tag=123412 Call-ID: 10275342@handbook.com CSeq: 2 SUBSCRIBE Contact: sip:server.handbook.com Expires: 3600 Content-Length: 0 M9: In order to complete the process, the notifier sends the subscriber a NOTIFY with the current event state of the resource. © 2009 by Taylor & Francis Group, LLC SIP Event Notification and Presence Information NOTIFY sip:user@handbook.com SIP/2.0 Via: SIP/2.0/UDPserver.handbook.com;branch=z9hG4bk8sdf2 To: sip:subscribe@handbook.com>;tag=12341234 From: sip:notify@handbook.com>;tag=abcd1234 Call-ID: 10275342@handbook.com CSeq: 3 NOTIFY Max-Forwards: 70 Event: XXX Subscription-State: active; expires=3599 Contact: sip:server.handbook.com Content-Type: XXXXXX Content-Length: [The state information of the resource] M10: The subscriber confirms receipt of the NOTIFY request. SIP/2.0 200 OK Via: SIP/2.0/UDP server.handbook.com;branch=z9hG4bk8sdf2; received=168.0.2.6 To: ksip:subscribe@handbook.com>;tag=12341234 From: <sip:notify@handbook.com>;tag=abcd1234 Call-ID: 10275342@handbook.com CSeq: 3 NOTIFY M11: The subscriber subscribe@handbook.com unsubscribe a subscription to the notifier notify@handbook.com. SUBSCRIBE sip:resource@handbook.com SIP/2.0 Via: SIP/2.0/UDP example.com;branch=z9hG4bknashds7 To: ksip:notify@handbook.com>;tag=abcd1234 From: <sip:subscribe@handbook.com>;tag=12341234 Call-ID: 10275342@handbook.com CSeq: 3 SUBSCRIBE Max-Forwards: 70 Expires: 0 Event: XXX Contact: sip:user@handbook.com Content-Length: 0 M12: The notifier for notify@handbook.com processes the subscription request. A 200 (OK) response is sent to confirm the subscription. SIP/2.0 200 OK Via: SIP/2.0/UDP example.com;branch=z9hG4bknashds7; received=168.0.2.5 To: