Which SIP reason phrase maps to SIP response reason code 181? 

Answer options:

A. Ringing
B. Call is Being Forwarded
C. Session in Progress
D. Unknown Number
E. Call Does not Exist

B

1xxProvisional Responses 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.[ ]:21.1.3 182 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 (including the User Agent Client (UAC)) that an early dialog has been terminated. Reference: http://en.wikipedia.org/wiki/List_of_SIP_response_codes References: http://en.wikipedia.org/wiki/List_of_SIP_response_codes