[Asterisk-Users] Re: call progress - what are the sticking points?

[Peter Svensson]

On Thu, 28 Oct 2004, Steve Underwood wrote:

> Stephen David wrote:
> >i don't have a specific bug in mind, i was just wondering WHY call progress doesn't work so well -- in particular, on analog lines.  ie. is it a hardware or software problem (or both).  with more info, i'd like to help to work out the kinks, for myself and everyone.  :)  
> >
> Back in the days of Stowger exchanges you knew when the called party 
> answered, by a reversal of the DC voltage on your analogue line. With 
> digital exchanges that stopped, and no solid feedback is given to the 
> caller on ordinary analogue lines. You have to infer that someone has 
> answered, and the reliability of that can be poor. Digital lines, like 
> ISDNand SS7, and protocols like MFC/R2 tell you positively that someone 
> has answered.

At least in Sweden pots interfaces in the pstn all have answer and 
disconnect supervision through polarity reversals. 

> If you had good results with Dialogic it was merely luck. Because they 
> have to infer the phone has been answered, their detection only works if 
> the calls follow their model of how someone answers the phone. Depending 
> on your circumstances, and the nature of the calls you make, it can be 
> hopelessly unreliable.

It could be that it handles answer supervision and that his pots line has 
tbat option as well.

Peter