N UA (User Agents);
N - (Proxy Servers);
N (Redirect servers);
N (Registrars Location servers).
UA (User Agents)
SIP, , . ; : - .
UA :
UAC {User Agent Client)
UAS {User Agent Server).
- (Proxy Servers)
Proxy - .
- , , . - . , , .. , - , , . - , , .
(Redirect servers)
IP- . , - . . . -, . .
(Registrars Location servers)
, SIR. REGISTER. : , . , , , - .
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SIP- .
, , - .
, , .
, , ., , . SIP :
, , , , Call-ID ( ), Contact (), CSeq ( /), Date (), Encryption (), From ( ), (), Via (), Record-Route ( );
, 'Content',, Content-Encoding ( ), Co 
ntent-Length ( ), Content-Type, ( );
, , , Accept (), Accept-Encoding ( ), Accept-Language ( ), Authorization (), Hide (), Max-Forwards ( ), Organization (), Priority (), Proxy-Authorization ( -), Proxy-Require ( -), Route(), Response-Key ( ), Subject(), User-Agent ( );
, , Allow (), Proxy-Authenticate ( -), Retry-After ( ), Server (), Unsupported ( ), Warning (),WWW-Authenticate ( WWW-).
SIP .
Content-Type . , , SDP, .
Content-Length .
()
n 
INVITE , ( ), . , , , .
n INVITE, , INVITE, .. , INVITE
n CANCEL , CANCEL Call-ID, , From CSeq, , .
n BYE . , BYE, () 200 .
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n REGISTER . , , From , Contact , INITE Expires, , ( , - 1 ). REGISTER Expires, 0, Contact.
n OPTIONS . .
() .
, , , 1 (provisional) :
n 100 Trying . , , , . CALL PROCEEDING Q.931;
n 180 Ringing - ALERTING Q.931
(2)
, 2, 3, 4, 5 6. , - .
n 2 (success) , . 200 . ;
n (redirection) , , ;
n 4 (client error) , ;
n 5 (server error) , - ;
n (global failure) , .
