1xx     Provisional 
100 --- Trying
180 --- Ringing
181 --- Call is being forwarded
182 --- Queued
183 --- Session progress

2xx     Successful
200 --- OK

3xx     Redirection
300 --- Multiple choices
301 --- Moved permanently
302 --- Moved Temporarily
305 --- Use Porxy
380 --- Alternative service

5xx     Service Failure
500 --- Server internal Error
501 --- Not implemented
502 --- Bad Gateway
503 --- Service unavailable
504 --- Server time-out
505 --- Version not supported
513 --- Message too large

6xx    Global Failures
600 --- Busy everywhere
603 --- Decline
604 --- Does not exist anywhere
606 --- Not acceptable

4xx     Request Failure
400 --- Bad request
401 --- Unauthorized
402 --- Payment request
403 --- Forbidden
404 --- Not found
405 --- Method not allowed
406 --- Not acceptable
407 --- Proxy authentication required
408 --- Request time out
410 --- Gone
413 --- Request entity too large
414 --- Request-URI too long
415 --- Unsupported media type
416 --- Unsupported URI scheme
420 --- Bad extension
421 --- Extension required
423 --- Interval too brief
480 --- Temporarily unavailable
481 --- Call/Transaction does not exist
482 --- Loop detected
483 --- Too many hops
484 --- Address incomplete
485 --- Ambiguous
486 --- Busy here
487 --- Request terminated
488 --- Not acceptable here
491 --- Request pending
493 --- Undecipherable