Replacing ISDN PBX but VoIP Asterisk


I am currently running a Euracom ISDN PBX on the German PSTN network. Also I have DSL.

This configuration I would like to replace by an Asterisk system, in the process getting rid completely of the expensive ISDN phoneline and using VoIP for all calls. I would however like to keep my internal ISDN bus with the existing phones as well as one analogue fax.

Can anybody give me pointers as to what kind of hardware I need for this application? I obviously would like to avoid expensive “professional hardware”.

I was currently thinking of following:

  • AMD 64 2800+ running at 1GHz
  • 256 MB DDR
    1 AVM B1 active ISDN card (apparently supported by linux)
    1 modem?

Following are my questions: (I am very happy to get an answer to just one of them…)

  1. Could I use the modem as an analogue Asterisk telephone port for the fax? Or how else can I connect the fax?
  2. If I wanted to connect the Asterisk box also to the existing ISDN PSTN to make sure everything is indeed running smoothly before I get rid of ISDN all together; can I just buy a second AVM B1 and use that as an external port? (I.e. any problems with two AVM B1’s?)
  3. How many telephone conversations can I have simultaneously in acceptable quality over a 128 KBit upstream connection?
  4. Are memory and processor suitable for this or are they hopelessly over-/under-scaled?
  5. Any other helpful pointers for somebody who is just getting started with Asterisk?

Thank you very much for your time!