DID trunk with FXO card

Before you ask, I’m not talking about a PRI here. This is a single incoming only trunk with 100 DIDs. When just one fax is being received, any of the other 99 DID numbers will get a busy signal when dialed.

One of my clients is using RightFax with a BrookTrout board. They have an Incoming DID trunk. Has anyone ever successfully configured an FXO device to work with a trunk like this? I’d like to ditch RightFax and set them up with Asterfax.

the question is going to be how the trunk signals the equipment as to what number has been dialled. find that out and you have the basis for replacing the current system with Asterisk and FXO hardware.

I have no idea what signaling setup to use.

I was hoping you or IronHelix had already played with this before…information about incoming DID trunks is sparse. I haven’t found anybody at the Telco that can tell me much about them either.

I was able to find this post:


He mentions a PRI, but it looks like he does have a one-way trunk or two. If he is describing the line type I’m interested in, it looks as though I would be terminating the line with an FXS device. I just happen to have a TA750 with four FXS cards in it that I could test this with. Though, I’d sure like to keep from frying them.

Here’s another page I found that may relate:


Thanks for the help sorting this out. Appreciate it!

sorry, i’ve never seen our telco offer anything like this. over here, if you want DID (or DDI as it’s known in the UK) you get a PRI, or ISDN-BRI if Multi Subscriber Numbering will suffice.

it sounds great, but i can’t help here.

Found the type of signaling it’s using:

T1 E&M Robbed Bit - Wink Start

That help?

I’ve never seen any FXS or FXO signaling setting that would appear to know anything about a DID.

Even if we were absolutely sure the signaling type is as I described earlier, would something like an X100P be able to figure out that part of the “chirp” was the DID or would it only know the CID? What about a TDM400?

there’s a lot of telecom experience on the -dev mailing list. in your shoes i would start a thread on that in this case.

My first brazen cross-post:


Digium have already posted that the devs don’t have time to visit these boards. i meant a post to the -dev mailing lists … see lists.digium.com

If this is an wink start E&M (ear and mouth) trunk, you will not be able to configure a FXO card to work. The line and signaling protocols are entirely different from a standard loop start line. Even the digits being sent to you on the trunk are probably MF instead of DTMF.

You will need a asterisk compatible card that supports an E&M trunk, but I am not aware of any. You could to build a simple E&M to Loop Start converter, but you may still have tone detection problems if the tones are being sent MF and the card you connect the converter to is expecting DTMF.

I did this one time with a TA 750 but I cant remeber wich one I hooked to the FXO or the FXS I think I played with both before I got it to work. As far as signalling you can change the cards in the TA. On the asterisk side you just set it up to match the T1 side of the Adtran I think I used D4 AMI. But thats going to be a waste if you just need this for 1 line

I’ve got a TA750 with FXS and FXO modules. Am I at risk of frying a channel if I hook this trunk to it? Which would you try first: FXS or FXO?

Dear Kheston,

How about your testing result? I am facing the similar choice as well. I would like to know what kind of hardware that I need to run with Asterisk and DID line.



Analog lines in the States do not provide the DID. Ain’t gonna happen. Only digital lines inform the PBX of the DID that was called.

Dear all,

Do you know what hardware needs for asterisk to use with DDI lines?

Thanks a lot.


If depends on what YOU call a DID
Not all “DID’s” are the same


Wouldn’t a T1 card, such as Digium TE110P, work for the original poster’s configuration? I haven’t used them at all, but the T1 interfaces I use on more proprietary systems (ahem Redcom cough) can be configured for E&M. Also, E&M trunks usually use DTMF to pass digits, the main thing is the wink in and wink out to seize/release the line.

sorry I’m late…

This type of line is very unusual, especially in the states. I have neither used one nor ever heard of anybody having one, ever.

I can tell you that an analog card like X100 almost certainly won’t work. I am pretty sure that the analog cards don’t support E&M but i could be wrong…

Sadly I can’t be much help here :frowning: the only thing I can maybe suggest is get an x100 and try it, the most you will probably fry is the X100 and that’s not a big loss.

There is certainly such a thing as a DID line in the states. I’ve got one running into a client site here in CA. It is one way only, incoming calls. The Brooktrout fax card it’s plugged into must dial out on another line.

The Brooktrout card in the ONLY card I’ve seen that knows anything about the DID trunk it’s plugged into. If I had a spare moment, I’d try to write an Asterisk driver for it. They go for about $400 on eBay, $2100 new.

All I have Rightfax doing is correlating DIDs with email addresses and sending a TIF to the user whenever a fax arrives. Something similar would be a piece of cake in Asterisk. It’s the DID signaling that’s missing.

I can’t find any clear instructions on how to set up my TA750 for use with the DID line or I’d try it.

yes, a T1 card from Digium or Sangoma would do the trick. and of course a (partial) T1 line from the telco. sounds like the T1 cards are cheaper than the Brooktrout fax card.

i’d recommend using iaxmodem and hylafax along with Asterisk. that’s what I use at my company and it works pretty well.