[asterisk-users] generating SIP errors

[Steve Cayona]

I have a DID vendor that wants me to be able to generate specific SIP 
error messages under certain conditions and I'm completely stumped on 
how to do these:

#1 - They want to see a SIP 503 error response(service unavailable) when 
they send the call in to an active extension and and the service is not 
available, I don't have a
clue on how to simulate this.

#2 - When they send in a call to an extension that doesn't exist they 
want to see a SIP 100 TRYING message before the receive the 404 NOT 
FOUND error.  Currently
I have only been able to generate the 404 error.

Any help, clues, tips or tricks are greatly appreciated in advance.  
I've searched the web for hours begging for scraps and still have come 
up empty handed