DAHDI specifications

Colleagues, tell me, please, where can I find the description of the DAHDI specification?
I want to read it before bed…

Thanks in advance,

I suspect DAHDI - Digium Asterisk Hardware Device Interface (DAHDI) - Asterisk Project Wiki is the closest
thing you’ll find to a “specification”.


Thanks, but that’s not what I’m looking for. I would like to find something like RFС - documents describing the composition, structure and technical sense.

The very most you are going to get is the README at GitHub - asterisk/dahdi-linux: This is the official dahdi-linux repository. All issues and PR should be raised here. and the .h file.

Thank you. Of course, I went to this page before asking the question. In fact, that’s why I asked him.

I have been working with DAHDI-compatible peripherals for almost twenty years, but for me it is an amazing discovery that during this time no one considered it necessary to write an abstract that allows you to understand the full picture, at least in an overview.

Agree that the situation when a well-known standard, moreover, advertised as open, needs to be studied almost by reverse engineering methods, this, tactfully speaking, is not quite normal.

It’s not a “well-known standard” or a standard by any means. It’s just open source.

I cannot agree with your point of view.

If more than fifteen years, when purchasing equipment, users check compliance with the standard, then this is a well-known standard.

The companies Digium and Sangoma produce and sell hardware at a very bourgeois price, and Asterisk, in fact, is just a free marketing application for this hardware. (Otherwise, no one will buy it.)

There must be some kind of social responsibility. I believe that writing a quality brochure describing DAHDI will not spend even a thousandth of the promotional budget.

Okay, it’s fine if you disagree. I don’t foresee any change in this area - though DAHDI is not my responsibility.

It would be more correct to say that I am disappointed.

Well, in that case, let me thank you for the answers, although they did not help me in any way.

I think it’s true to say that a very large number of both Open Source and
Proprietary projects are based on protocols, APIs, hardware interfaces etc
which are neither “standards” (not even RFCs) nor necessarily well-documented.

I do not think the Asterisk project is unusual in using an implementation such
as DAHDI without it being based on something end users can check compliance

I suggest examples of this are corosync, pacemaker, Icinga, Grafana - just the
first ones which come to mind.

Not everything is as neatly and thoroughly defined as SIP.


That’s also true, of say, Microsoft Windows. To properly specify most software, you would need to provide details of internal state machines, whereas most software documentation only describes interfaces in isolation, often not including all error cases.

One of the big advantages of open source is that you can actually get a white box solution to the full de facto specification.

Really good documentation for modern, proprietary, tech tends only to be available at the ASIC chip level. Whilst a lot of products are just applications of those ASICs, you won’t be told what the underlying ASIC is and what customisation have been selected, and these may change through the products lifetime.

Great gods, what do I hear? Is DAHDI already being discussed as a proprietary technology?

Isn’t it time to talk about the creation of the OpenDAHDI specification?


I was making a general comment about documentation, and particularly about the poor documentation of non-open, end user, products.

However, DAHDI exists to interface with proprietary tech, namely the various Digium and now Sangoma, circuit switched telephony cards. It’s not being provided to assist competing hardware manufactures interface with Asterisk.

Basically, with open source code, if you don’t like the documentation, you write your own documentation and submit it to the project.

Unfortunately, what tends to happen instead is that people see a business opportunity, and rather than creating free reference documentation, they sell a cook book (by which I mean one that gives example uses, but doesn’t explain the fundamentals, or attempt to be complete.

I’ve currently been learning Blender, which is the de facto open source “standard” for 3D graphics and animation, and I’m finding that the official documentation is not sufficiently detailed, the on screen tooltips are cryptic, and the (second hand) “complete guide” I bought turns out to be a cook book, which spends far to much time repeating basic procedures, and makes far too much recourse to saying you need to experiment to work out what the options do (I got the impression that its author often didn’t know what they did).

Open source is also particularly prone to lack of documentation, because a lot of it is written by programmers on a non-commercial basis, and programmers don’t like writing documentation. However, I was pointing out that this was mitigated by the fact that proprietary software documentation is often too incomplete to be useful, but the ultimate documentation, the source code, is available for open source.

In terms of what Sangoma do, whilst I have no knowledge of their internal politics, they are business, and software businesses generally can never afford the resources needed to do everything that ought to be done, so they are continually prioritising work, based on the business impact of not doing it.

Even where standards exist, big companies sometimes get them wrong, and because they are big, their implementation then becomes the de facto one. Also, a lot of businesses quote standards that they have never read, and are sometimes inappropriate, relying on upstream suppliers’ claims.

Finally, you directly called a spade a spade.

The most terrible nightmare of companies Digium and Sangoma is Chinese Internet auctions littered to the very roof with 100% compatible equipment for Asterisk. And all for three cents.
(However, something tells me that consumers will not begin to feel sad about this …)

Also, if my memory serves me, the antitrust laws of the US and Canada quite rightly call such a situation a monopoly and take measures to destroy it.

Great comparison. Very imaginative and memorable. If you don’t mind, I will always quote you to students. If you want - with the indication of the author.


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