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[HLL] Re: VP1 Comparison



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Hi,


> First an intro. I am Lucky, I have done crypto since 1989 and I have
> extensive experience with digital telephony and isochronous protocols. I
> am a long time subscriber to the Cypherpunks mailing list. [Hence the
> domain cypherpunks.to :-]

Good morning  :-)

> > i had a quick look at the protokoll-specs for the "VP1"-Device.
> What is the VP1 device and where can I find the specs?

It's the device made by comsec. They call it "VP1" in the specs.
So we are talking about the specs for "GSP8191", i suppose.

> > * They operate their 14400-Modem is *synchronous* operation.
> Sure. 14.4 sync mode is the only way you can fit a  GSM 06.10 full rate
> speech transcoder (13,000 bits/sec) plus protocol overhead into a V.32bis
> connection. If you go async, you have to use a lower voice quality codec.
> The next fallback is something around 7200bps. Which makes a huge
> difference in voice quality.

We would like to use a standard-144-modem.
These modems use V32bis and are therefore synchron "on the line".
However VP1 has a direct "synchron" connection to the modem-chip.
In our case this synchronous data is converted to asynchron.
While this does not change the baud-rate (we can still use gsm-full-rate),
it changes several aspects for frame-synchronisation.
These differences to aquire and maintain sync were what i meant.


Volker

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