Pseudorandom Hashing

[Rich Grise]

Build a call center recorder for digital phones. It needs to be able to
tap the lines and record the incoming & outgoing audio. It basically
consists of a bit receiver, packet parser, some glue logic and a big
serial interface to a DSP which does mu-law expanding & compressing.
The DSP then sends the audio out on a PCI bus to be recorded on disk.

I'm adding a new brand of PBX interface to the thing and it appears that
the audio data is scrambled -- I don't get a sensible signal when I'm
hearing dial tone, and the data is scrambled in the patterns described
above when there is "silence" on the line.

What is it you mean by "don't get a sensible signal when ... dial tone"?

Is it not in the same format as the pattern described above? Or is it
just a scrambled dialtone? I'd think that'd give you another baseline
point to help zero in on your algorithm.

Another thing I remember, I'm pretty sure it was in Don Lancaster's
TTL Cookbook, was a chart with some repetition cycle "times" for
various feedback patterns, i.e. picking off different bits from
the shift register(s) to xor together will give you different
scrambling patterns.

Sounds like a way fun project! Need a subcontractor?

Good Luck!
Rich