[VoIP] Congestion vs Hangup in Asterisk

[Chad Perkins]

On 12 Sep 2007 at 23:46, Greg Blakely wrote:
> Hi, folks.  
> I'm looking for a distinction between CONGESTION and HANGUP, and when
> each should be used.
> 
> CONGESTION is defined as "send congestion notification and wait for
> hangup,"  while HANGUP is pretty simple: "Disconnect the call."
> 
> Okay, so I know that I can use HANGUP everywhere, and things will work
> smoothly.  But I'm wondering where CONGESTION would be more
> appropriate.
> 
> And, it has to be asked, is CONGESTION sent towards the originating
> end?

Yes.

> If so, would it apply only to incoming calls?

All calls are incoming as far as the Asterisk dial plan is concerned.

>  Incoming from where?

Anywhere and everywhere.

> a PSTN line?

Yes.

>  an extension?

Yes.

As John C. has noted, exactly what is sent depends on the technology, but in general 
congestion tone is sent to analog channels (by the Zap driver?) and a status 
message sent to digital channels (for the initiating device/system to process).

> My head hurts! 

It gets better.  If the call originated in (an) Asterisk and was un-suped at the 
destination, then execution continues after the Dial command (and ${DIALSTATUS} 
will have a value of CONGESTION, etc.).  In this case it becomes difficult to know 
how far the call got before it was "terminated" without looking at other things.

Chad
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