[asterisk-users] ringing... or lack thereof

[Jeff LaCoursiere]

Want to make sure I understand why a caller might not hear "ringing" when 
outbound calling.

A SIP phone is behind a firewall and is registered to an asterisk 
server on a public network.  Sometimes (but not always) when placing an 
outbound call there is no ringing before the remote party answers.  Its 
not that the remote party picks up very quickly - the delay may be as long 
as twenty seconds before it is answered (and I must assume that the remote 
phone had rung at least a few times).

I vaguely understand that part of the SIP call setup includes a "ringing" 
message, sent from asterisk to the originating phone.  If this is correct 
and the firewall for whatever reason isn't passing this message, will 
there be no ringing sound on the originating phone?  This is confusing to 
me, as I kind of assumed that the ringing sound was in audio, and would be 
part of the RTP stream.  But perhaps that isn't even flowing yet.

Guess I am showing my SIP ignorance.  Please enlighten ;)

Cheers,

j