SIP Message transaction

In my previous post i mentioned the basic architecture of a SIP network and the component involve in SIP .
In this post i am going to mention several messages that the SIP uses to initiate and drop a call.

SIP works on request/response model

The most common messages used by SIP are as follows

Register: UA (User Agent) send a message about its location to SIP server in register message
Invite: This message is sent by the caller in order to other agent to join a SIP call , This message can also be used in order to change any call parameter for a established call.
ACK : The SIP UA receive several response for a invite , This message acknowledge the final response
CANCEL: This message end a call that has not yet been established
BYE:  This message end a session or decline to take a call
OPTION: This message queries about the capability of the server.

Response for a request in SIP fall under the below categories:

1XX : This reponse designate a provisional and informational message
2XX: This response designate a  repsonse to a request  that is successful .
3XX : This response is used to designate a redirect or location change for the called UA
4XX: This response is used to designate a error condition from UA side (Request failure)
5XX: This response is used to designate a failure condition from the Server Side
6XX: This response is used to designate a global failure

Informational response:

100 Trying
180 Ringing
181 Call Is Being Forwarded
182 Queued
183 Session Progress

Success

200 OK

Redirection
300 Multiple Choices
301 Moved Permanently
302 Moved Temporarily
305 Use Proxy
380 Alternative Service

Client-error

400 Bad Request
401 Unauthorized
402 Payment Required
403 Forbidden
404 Not Found
405 Method Not Allowed
406 Not Acceptable
407 Proxy Authentication Required
408 Request Timeout
410 Gone
413 Request Entity Too Large
414 Requested URL Too Large
415 Unsupported Media Type
416 Unsupported URI1 Scheme
420 Bad Extension
421 Extension Required
423 Interval Too Brief
480 Temporarily Not Available
481 Call Leg or 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

Server-error

500 Internal Server Error
501 Not Implemented
502 Bad Gateway
503 Service Unavailable
504 Server Timeout
505 SIP Version Not Supported
513 Message Too Large

Global failure

600 Busy Everywhere
603 Decline
604 Does Not Exist Anywhere
606 Not Acceptable