Interfacing with Analogue PBX via FXO

Hi All,

I was wondering if someone would be able to help - we have a requirement to interface Asterisk with an existing analogue PBX via a small number of analogue extensions (4-8 max). It’s important that whatever solution we find supports redirection on the legacy PBX (i.e. recall functionality to instruct the PBX to transfer the call to another extension and clear down the call to Asterisk, leaving the line clear). Obviously this is just for incoming calls from the analogue PBX.

I’ve found a few FXO gateways that look good, but it’s not clear if they will support the recall functionality. I’m guessing that an internal FXO card should support this. DPNSS is out of the question for various reasons - must be FXO only.

Has anyone here come across the same requirement? If so could you let me know what kit you’d recommend? The cheaper the better.

Thanks in advance.


What kind of PBX are you using. Please share your details we will discuss or PM me. I will help you.




I’ll echo david55’s comment. If someone’s offering to help you via PM, then that’s detrimental to the board. It means that if they do help you, without trying to charge you money for consulting, then the rest of the board doesn’t benefit from the answer to the question. That’s not good practice.

Ah ok cheers guys, keetan I’ve sent you a PM (before I read malcommd’s post).

But in answer to the question, the PBX we want to talk to is an ISDX.

We’ve been looking along the lines of the Grandstream GXW-4108 FXO gateway, but not sure if it (or similar) will be able to handle the recall functionality?



We will discuss here.

You need to takes the extension lines from the PBX and put into your FXO board. Need to do some dial plan programming in Asterisk to handles the call as well transfer to the PBX extensions.



Can the iSDX be configured for timed break/hook flash recalls? We always used them with earth recall and I don’t believe Asterisk supports that. Although I don’t use analogue interfaces, I believe all local ones support hook flash generation. I have a feeling that most are physically incapable of doing earth recall.

Asterisk has no high level support for this sort of operation so you will need to explicitly use “DTMF” to generate all the signalling to achieve this.

Although we use iSDXes, in house, we interface with a gateway (Applianx, I think) to a common channel signalling interface (DPNSS, I think) and we only redirect the speech path (Asterisk directmedia). I don’t deal with those aspects of the system myself. Some of the reasons for our configuration are not generally applicable.