The Sip Response codes - Codes establishing a connection.
100 Trying - Extended search being performed may take a significant time so a forking proxy must send a 100 Trying response
180 Ringing - Destination user agent received INVITE, and is alerting user of call
181 Call is Being Forwarded - Servers can optionally send this response to indicate a call is being forwarded
182 Queued - Indicates that the destination was temporarily unavailable, so the server has queued the call until the destination is available. A server may send multiple 182 responses to update progress of the queue
183 Session in Progress - This response may be used to send extra information for a call which is still being set up
199 Early Dialog Terminated - Can be used by User Agent Server to indicate to upstream SIP entities
200 OK - Indicates the request was successful
202 Accepted - Indicates that the request has been accepted for processing, but the processing has not been completed
204 No Notification Indicates the request was successful, but the corresponding response will not be received.
300 Multiple Choices - The address resolved to one of several options for the user or client to choose between, which are listed in the message body or the message's Contact fields
301 Moved Permanently - The original Request-URI is no longer valid, the new address is given in the Contact header field, and the client should update any records of the original Request-URI with the new value
302 Moved Temporarily - The client should try at the address in the Contact field. If an Expires field is present, the client may cache the result for that period of time
305 Use Proxy - The Contact field details a proxy that must be used to access the requested destination
380 Alternative Service - The call failed, but alternatives are detailed in the message body.