[Asterisk-doc] Added some ISDN documentation

[Jens Kübler]

> Jens, thanks for your submission! We have not ignored you, we're just
> trying to figure out the best place to fit your work.
>
> The challenge we have is this:
>
> Volume One has the goal of helping a user through setting up four
> interfaces: SIP, IAX, FXO and FXS. What you have submitted falls outside
> that scope.
>
> Having said that, I think it would be agreed that the documentation is
> very North American in its focus. In order to serve a more international
> audience, having contributors from elsewhere is very valuable to us.
>
> The challenge: is ISDN something that would be valuable to the newbie?
> In North America, there will be very few newbies who would use ISDN-BRI,
> so from that perspective it does not fit this book. In Europe, that
> might be a very common set up for a newbie, and thus it would definitely
> fit this book. But in that case we may need to re-think many sections.

ISDN is the core standard for telephony service here in Europe and in several 
countries around the world due to political influence.
For Germany there is an availablity of 100% as the main telco Deutsche Telekom 
pushed really hard to establish the standard back in the 90s. Italy has used 
a different protocol for ISDN some time ago so they must be using it, too. 
Just some days ago I helped out a guy from Portugal with ISDN which means 
that they also have to have it.
It took me a long time to figure out what your FXO and FXS interfaces are good 
for.
Howewer there is still the old fashioned analogue lines here in germany but 
predominantly in areas where you wouldn't be interested in setting up an * 
server.

>
> Either way, we want to talk to you about your ideas. If you can give us
> a better understanding of how Asterisk is used in Europe, that will be
> very valuable. Perhaps ISDN-BRI in Europe deserves it's own chapter, but
> for sure we need to think about how to fit your contribution into the
> document as a whole. Simply patching it in where you've put it might not
> be the best place for it, and if we put that in, we're going to need to
> support it elsewhere in the book as well, and that means we'll need more
> writing from you.
I'm using * for six month now for evaluation so I think I can contribute some 
more. The -users mailinglist is getting really busy due to the fact that the 
"read the source" comments aren't users really helping out so there needs to 
be a good documenation.

By the way: Am I missing a real good html doc of asterisk on the web? (please 
don't mention voip-info  - everbody throws his/hers half knowledge in there)
I can't find a short reference with the currently available options - 
something like the postgresql doc were hints are given since when version 
which feature occured and something with a well defined structure.
I need minutes to find the correct link in voip-info.

Jens