No ring Back when login.

Hi All,
I am not getting any ringback when trying to login in to the campgin.
Asterisk output is..
channel.c:2496 __ast_request_and_dial: Unable to request channel SIP/3333
I am not getting any ringback when trying to login in to the campgin.
Asterisk output is..
channel.c:2496 __ast_request_and_dial: Unable to request channel SIP/3333