ISDN <-> Asterisk <-> PBX || Bridge togheter

Hello folks !

I need to put an Asterisk server between our main ISDN Lines (4 BRI with 8 simul. calls) and our actual PBX, as we need to filter phone calls (who can call us, at what time he can call us, etc.) without replacing our actual infrastructure.

Someone could think that it would be better to replace PBX; this filtering solution should be considered a test and it should be removed shortly (1 month or 2), so we can’t replace anything inside.

What hardware could I need to make a bridge between my ISDN lines and actual PBX using Asterisk?

Best regards.

Your asterisk server would need at least 1 network card that would connect to your PBX as it is.

Also to catch the ISDN line youll need an Analog card. you might even be able to connect ISDN and the PBX via the analog card. all depends on how much ports the card has :wink:

for configuration, i dont know if what you are trying to do is possible, do post here if it works aye :wink:


For this you will need 2 4port BRI cards or use external gateways such as Pattons.

I have done this many times with E1s but the the its the same for BRI.

The dialplan can be as simple or as complicated as you like realy , Either timed or matching CLI etc. Its just normal dialplan.

Any problems just ask


Hi ianplain,

thanks for your post.

According to your solution, do you think that I could keep safe Caller IDs, or will I loose them during bridging ?

Do you have a sample configuration of all the solution so I could keep all togheter and start tests ?

Best regards !


Cli has been preserved in all cases.

Asking a bit much here aren’t you !

Basicly you set up an incoming context that does the matching and filtering and a outgoing context passing calls back to the network.

What goes in the incoming context is dependant on what you want to do.


Hi ianplain,

thank you for your answer. I understood what I need to do. It seems less complicated than I tought.

I hope to give the forum a positive feedback on this job (as COpeter required).

Best regards.

Hi ianplain,

according to your knowledge, if I have a green number that is routed on an ISDN line (our telephony company offer us this service), is there a way to intercept Caller ID and immediately hangup the calling without answering and without paying connection fee ?

We would like to filter (with the Man In The Middle) an ISDN Connection where there are calls directed to a green number.

I hope that I explained the problem using my poor english !!!

Best regards.

i didnt “require” it. its usefull for other people who might want to make the same :wink:

as for your green number. i think it should be doable with a simple dialplan that only hangs up if someone calls that number.

What country are you in?

It would be easier to find a carrier with a hosted PABX (with ISDN failover), port the numbers to them and do all the routing rules on their side, then present the calls to your existing equipment.

Alternatively, get a 1300 number and use this as the new advertised number pointing to a new hosted PABX number, which can then route your calls to your existing BRI.

Othewise, I would definitely advise you to find an asterisk consultant with BRI experience and proceed with the upgrade of your equipment.

Asterisk is very reliable, and depending on the state of mISDN, so are certain versions of drivers. I haven’t installed past 1.4.11 with BRI in 3-6 months.

Lastly, update to a PRI circuit. It’s got more support, more documentation, and it’s only an extra 2 channels.