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Asterisk-Users: Steve Underwood posts details on SpanDSP

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Author: Matt Riddell
Daily Asterisk News
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Steve Underwood has posted details of the changes in the 0.0.2prexxx versions of his SpanDSP code. Here's his post:

Some people have been using spandsp-0.0.1k in production systems for months. The main problems have been:

  • Canon fax machines often gave problems
  • HP machines are buggy, and with spandsp the bugs cause black streaks on received documents.
  • People get pages chopped in half.
You won't really notice the load caused by one channel of spandsp's fax machine on most modern CPUs. I had 100 channels running on a dual Xeon at one point, but I haven't tested recent versions at high loads.

With the latest spandsp-0.0.2pre4
  • The bug affecting Canons seems to be resolved.
  • The software used to rely on the internals of libtiff to compress and decompress images. Now it uses its own code which works around buggy machines likes the HPs, and allows better reporting of the received data quality.
  • Of all the pages getting chopped problems I received, one turned out to be a stability issue in the modems. This seems to be resolved.
Every other report of pages getting chopped, that I have investigated, has been due to timing problems in * or the hardware. This is probably about 30 examples now. There is nothing I can do about this. If spandsp does not work in these cases, neither will hardware modems and HylaFAX with the calls passing through *. Modems just cannot tolerate hiccups in the audio stream.

The long delay between spandsp-0.0.1k and the recent spandsp-0.0.2prexxx versions has been due to the fact that spandsp-0.0.1k has been working pretty well for a lot of people. There wasn't a need for many minor releases. 0.0.2 is a fairly major update, with many areas of the software changing in major ways. Some of these are complete, and some are still works in progress.
  • The modems have been reworked to get closer to the theoretically achievable performance on noisy lines. Their compute requirements are also a bit lower now.
  • Fax compression and decompression has been added.
  • An incomplete skeleton for class 1 modem operation, to work with HylaFAX, has been added.
  • A nearly working V.17 modem has been added. This still needs improvements to the receiver carrier locking to make it work properly.
  • A half finished V.22bis modem has been added. A couple of people asked for this, so allow integration of things like credit card validation machines with *. Most of these still sues V.22bis.
  • Variable speed playback of speech files. This is something a lot of people ask for, but which is fairly useless in practice :-) . Its just to play with, though.
  • A number of little modules, such as V.8 processing, have been implemented, tested, and added to spandsp, but are not really being used right now.
Regards,
Steve


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