ty.org: 5060 ;branch=z9hG4bK334241;received=24.32.1. 3 To: P. L. Chebychev sip:chebychev@academy.ru>;tag=21171 From: M. Poisson <sip:poisson@probability.org>;tag=25140 Call-ID: 58dkfj349241k34452k592520 CSeq: 1027 NOTIFY Content-Length: 0 Now that Chebychev knows that Poisson is on-line, he sends an instant message to him using the Contact URI from the NOTIFY: MESSAGE sip:s.possion@dist.probability.or SIP/2.0 Via SIP/2.0/TCP lecturehall21.academy.ru 5060 ;branch=z9hG4bk3gtr2 Max-Forwards: 70 To: M. Poisson <sip:s.possion@dist.probability.org> From: P. L. Chebychev <sip:chebychev@academy.ru>;tag=4542 Call-ID: 9dkei93vjq1ei3 CSeq: 15 MESSAGE Allow: ACK, INVITE, CANCEL, BYE, NOTIFY, SUBSCRIBE, MESSAGE Content-Type: text/plain Content-Length: 9 Hi There! Notice that this MESSAGE is sent outside the dialog. Instant messages sent using the MESSAGE method in SIP are like page messages-they are not part of any dialog. As a result, each message contains a new Call- - ID and From tag. The 200 OK response is used to acknowledge receipt of the instant message: SIP/2.0 200 OK Via SIP/2.0/TCP lecturehal121.academy.ru: 5060 branch=z9hG4bk3gtr2;received=19.34.3.1 To: M. Poisson <sip:s.possion@dist.probability.org>;tag=23 From: P. L. Chebychev <sip:chebychev@academy.ru>;tag=4542 Call-ID: 9dkei93vjq1ei3 CSeq: 15 MESSAGE Content-Length: 0 SIP: Understanding the Session Initiation Protocol Poison answers with a reply, which is also sent outside of any dialog, with a new Call - ID and From tag (an instant message response is never sent in a 200 OK reply to a MESSAGE request): MESSAGE sip chebychev@academy.ru SIP/2.0 Via SIP/2.0/TCP dist.probablilty.org 5060 branch=z9hG4bK4526245 Max-Forwards: 70 To: P. L. Chebychev k<sip:chebychev@academy.ru> From: M. Poisson <sip:s.possion@dist.probability.org>;tag=14083 Call-ID: lk34452k592520 CSeq: 2321 MESSAGE Allow: ACK, INVITE, CANCEL, BYE, NOTIFY, SUBSCRIBE, MESSAGE Content-Type: text/plain Content-Length: 30 Well, hello there to you, too! which receives a 200 OK reply: SIP/2.0 200 OK Via SIP/