[Asterisk-Users] existing ISDN PBX <-> asterisk <-> 2xBRI for IVR and SIP

[Peter Svensson]

On Tue, 26 Jul 2005, Alex Ongena wrote:

> I'am new to * and googled/read a lot, but did not find (yet)
> a lot of info to do the above.
> 
> Some months ago, I did find a 'story' from somebody having
> put * between his PRI and current PBX as IVR, but I can not
> find it back :-(

We have an Asterisk pbx between the PSTN and our old pbx. Lots and lots of 
details to get right, but just take your time and work through them.

* Thing through your dialplan in advance. 
   * Which number goes where. 
   * How do you dial from one system to another. (This depends to a large 
     degree on your existing pbx)
   * Most user prefer the dialplan at each pbx to be prefix-free (see
     http://en.wikipedia.org/wiki/Prefix-free_code) i.e. that you dont
     have both 345 and 3456 as valid extensions at the same time.

* Get the details on the isdn signalling
   * How many digits and which numbering plan are incoming/ougoing 
     called numbers and callerid delivered/expected.
   * Which signalling format (since you use BRI I expect it to be 
     EuroISDN).

* Get the timing right. 
   * You will almost certainly accept timing from the PSTN and provide 
     it to the other pbx.
   * Multi-bri cards can take the timing from the PSTN and provide an
     identical clock to the other pbx. This preevents bit-slips and is 
     a good thing.

Peter