Access Server

With thanks to for their excellent service.

The Access Server controls a pool of modems and waits for incoming calls. It then connects these calls to a remote tcp socket. The program runs under Linux and boots off a single floppy disk. With a multi-port serial card it could be useful to ISPs but that's not all . . .

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What it does
- Requirements
History
Scratching The Itch
Some Other Applications

What the Access Server Does

Access Server is a suite of programs that does a couple of things:

It is an "access/terminal server" which connects incoming modem connections to remote TCP sockets. Scenario: An ISP has a bank of modems attached to a PC with a multi-port serial card. A caller connects to one of the modems. The Access Server registers the call, allows the modem to answer and connects the modem to a remote Radius Authentication application. All this time, a manager is able to see a GUI representation of the call load, which modems are busy and how many failed connections were registered in the last hour.
It is a testbed for a VoIP (Voice-over-IP) system that uses the voice recording and playback features of current voice modems

Requirements

The idea is to develop a gateway between telephone networks and IP networks. It should:

Be like an appliance - put the disk in, switch on the computer, forget!
It should be simple and act sensibly when things go wrong (e.g. power cuts)
Run on low-end hardware.
It should be possible to use it as a gateway to things other than just the PPP protocol.
Configuration and management must be possible from a a remote location.
When one is trying to get one of these servers running one needs an interface with which it is easy to make changes.
It's always very important to keep a check on how well it is running so the management program's user interface should present the vital information simply and quickly.

The Access Server Project addresses these requirements by the following means:

It offers a web management interface via a tiny embedded web server. This allows the status of individual modems to be viewed from a web browser as well as permitting modems to be enabled and disabled, or reset etc.
It runs on linux, and is booted off a single floppy disk. It configures itself and automatically finds available modems - this is useful in the case of power failure as it will simply reload and carry on working when power returns.
Installation is as simple as editing a small config file on the floppy disk to specify an IP address for the machine and for the remote TCP service, inserting the disk into a computer and powering on.

Please ask questions so I can think of more to write!

History

I started writing Access Server to scratch an itch. My office used a Xyplex(TM) Access Server 720. We were running a dial-in service using a proprietary protocol. The modem rack had 4 modems and there was no chance of buying any more since the company that made it was sold and the model discontinued.

I spent a long time trying to work out how to attach a plain old external modem to the Access server as a quick fix. I'm from Zimbabwe and we don't buy new things like modem racks here without a more than excellent reason.

Anyhow the experience was miserable. The 720 has an extremely arcane command language, some commands activate immediate changes while some activate delayed changes and it's very hard to know which is which.

Our server ran a program which received the raw data from the incoming modem (via a TCP socket). This program was responsible for managing the proprietary protocol that the caller spoke.

Simply setting the port to make a raw (untranslated and unfiltered) connection to a remote port was hard even though I copied the 720 port config from one of the existing modems to the port of the new external modem.

Scratching the Itch

To cut the story short, I decided that this was a terrible waste of time. So I decided to write an Access Server myself like so:

Wrote it in Linux - reliable, customisable.
It boots from a floppy disk which makes everything simpler for Windoze types because they don't have to install anything. In addition it can run on machines without hard drives like the old bit of junk in the corner that nobody can find a use for.
Uses static linking and cram all the functionality into a single executable which runs as the init process - this saves one from the pain of stripping down the C library to fit on a compressed ramdisk image. It means that you can use the same C library as you use normally on your Linux machine.

Some Other Applications

Well, first problems first for me but some interesting alternative uses for an Access Server of this type have popped into mind.

There is, of course, the standard kind of thing where the access server runs pppd for every incoming connection. This could be done by Access Server as well. It's modem-autodetection feature and remote management features (when they are written) could make it a worthwhile alternative to the many other getty's out there.

Then the other area that I'd like to explore is VOIP. Currently lots of people have voice-modems. I'd like to explore the possibility of setting up a few of these as "input" points from the Plain Old Telephone System (POTS), transferring the information via the internet to an "output" point.

VOIP is a magic thing for people in the third world. Overseas telephone calls can be ruinously expensive, but businesses everywhere need to make them every day - particularly those with export/import focus. People could use products like Netmeeting but these require a computer with an internet connection and they're a pain to learn to operate and the person you're trying to contact has to have the same thing. It would be much simpler if people could use just their telephone to do it.

Of course this has been done already but it's not ubiqitous yet and the cost is not all that low.

Anyhow we'll see. I'm having a lot of trouble interpreting the formats that my USR Sportster Voice records.