2N VoiceBlue Next v3.0 - Manual (Page 31)

IP Voice Transmission 2.4
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The answers to the SIP messages are numerically coded as the case is with the http
protocol. Below are the most important ones:
 1XX – information messages (100 – trying, 180 – ringing, 183 -
progress);
 2XX – successful request completion (200 – OK);
 3XX – request forwarding needed (302 – temporarily moved, 305 – use
Proxy);
 4XX – error (403 – forbidden, 486 – busy here);
 5XX – server error (500 – Server Internal Error, 501 – not implemented);
 6XX – global failure (606 – not acceptable).
VoIP SIP Phone VoIP SIP Phone SIP Proxy
SIP/SDP INVITE
SIP/SDP INVITE 100 Trying
183 Session progress
183 Session progress
200 OK
200 OK
SIP ACK
SIP ACK
SIP BYE
SIP BYE
200 OK
200 OK
RTP Stream
SIP Message Sending during Call Set-up and Cancellation