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

Which SIP reason phrase maps to SIP response reason code 181?
A . Ringing
B . Call is Being Forwarded
C . Session in Progress
D . Unknown Number
E . Call Does not Exist

View Answer

Answer: B

Explanation:

1xx―Provisional 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. [1]:§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