Testing telephony DSP

The need

Telephony DSP needs testing in multiple ways. The test suite for spandsp, for example, can test a lot of telephony DSP functions. However, there comes a point where real end-to-end networking testing is needed. The standard industry method is to use two test sets made by Spirent's Telecom Analysis Systems (TAS) division. When bought new, these probably cost an arm and a leg. In the used market they can be picked up at reasonable prices.

The solution

So, I acquired a TAS1200D telephone network emulator and a TAS240 subscriber loop emulator. Some grateful users of iaxmodem+hylafax helped with the cost. I'd like to offer a big THANKYOU to them. Together these machines have been the mainstay of development testing V.34 and V.90 modems over the past few years. The general picture in the second hand test equipment market is the equipment can be in fine condition, but the manuals and any accompanying PC software have disappeared. This can be a problem.

I acquired the TAS1200D, which absolutely must be computer controlled, with its key manuals. One fairly important, but not vital, manual was missing. If anyone can get me the manual for the Universal Central Office (UCO) I would be very grateful. I have enough material to program the main functions of this machine. I do not have the software. I have started building open Linux software to drive this machine.

I acquired the TAS240 without manuals. It is controllable from the front panel, so manuals for the programming interface are less critical. It turns out al the machine's software is in a socketed 27512 EPROM. I read that in a programmer, scanned for all the strings, and didn't take too long to figure out all the instructions to control it from a computer. However, if anyone can get me a copy of the manual, I would be very grateful. I have started building open Linux software to drive this machine.

The software

The software has only reached the stage where it can only basically exercise all the features of the instruments. However, in the hope there might be someone out there trying to adress the same need, I am starting to make tarballs available of the work to date.

The code can be found here.

Acquiring test equipment

Someone asked about acquiring test equipment, so here is my experience from the current acquisition, in the hope it might help someone....

It has been some years since I last did this, and I wasn't sure who I should trust. The condition of equipment can vary a lot, and if it doesn't work, repairs might be a nightmare. Also, its really hard to know what a fair price might be when negotiating. Popular items, like oscilloscopes, tend to fetch a large percentage of their new price. More specialist things tend to be pretty cheap, especially if the world has changed rapidly, and the item is no longer hot.

After missing out on a couple of E-Bay auctions, I found a TAS1200D listed at www.dotcomrecycling.com. I had never dealt with them before, but the experienced was pretty good. They answered questions well, gave good information about manuals and software, and supplied scanned copied of the key manuals. They packed the unit well, and it arrived on time and intact. The price seems pretty reasonable, considering the young age and good condition of the unit. Please note that this recommendation is based on only a single transaction with this company. Don't complain to me if you have a less satisfactory experience.

I got the TAS240 in an E-Bay auction. It was a lab's leftover item, and not from a dealer. The price seemed OK. They packed it reasonably well, but parcel hurlers being what they are, a piece of plastic was broken off in the box when it arrived. Thankfully, this piece is mostly decoration, and the unit functioned OK. Buying in this way, i did not get any manuals. It doesn't seem easy to acquire manuals for things like this. There are several web sites offering test equipment manuals, but most of the ones they have are for very common items like scopes. If the nature of the equipment makes the manuals, or some supporting PC software, a necessity, E-Bay is probably only a useful if the offer page shows the manuals - and make sure it shows enough of them.