From: Timothy Newsham <newsham@wiliki.eng.hawaii.edu>
Date: Tue, 25 May 93 16:24:57 PDT
To: uri@watson.ibm.com
Subject: Re: PGP voice encryption
In-Reply-To: <9305251805.AA19930@buoy.watson.ibm.com>
Message-ID: <9305252324.AA29081@toad.com>
MIME-Version: 1.0
Content-Type: text/plain


> 
> Timothy Newsham says:
> > The biggest problem is CPU power.  The compression schemes that work
> > best are very computationally expensive.  Add to that the fact that
> > you need to do simultaneous encryption and compression, and if you
> > want full duplex make that simultaneous encryption, decryption,
> > compression and decompression.   You also have to send it over the
> > modem, and probably frame it too.
> 
> You're right.  But if the voice-modem,  or a smart voice card (like
> SoundBlaster, maybe? Can it do CELP? Can any other available card?)
I'm not sure.  My understanding of SoundBlaster was that it could
produce sounds and had digitizing capabilities (ie. A/D D/A card)
If this is so it couldnt do any computations itself.  Somoene
mentioned Xyxel's modems will do CELP in and of themselves.

> will handle full-duplex voice in and out, and then a smart data
> modem will pump it through the line (again, full duplex), then
> all the CPU has to do is simultaneous encryption/decryption,
> plus frame management (moving frames to/from Blaster and
> modem).
There is no doubt that the CPU can handle the encrypion +
framing, this is what I plan to do.

> 
> Am I missing anything?
> 
> > I'm currently implementing one scheme (LPC) on a DSP chip.  Hopefully
> > my end product will be <$50.  I plan put its own ADC/DAC chip on
> > board (to save computer<->DSP bandwidth).  Possibly some
> > high end CPU's like 486 and 040 could handle the load, but
> > wouldnt leave much cpu for anything else.
> 
> What DSP are you playing with? How expensive is it? Can I buy
> such a chip from somewhere (assuming the price won't scare me
> out)?
I am using the ADSP2105 from Analog Devices.  The list price
is about $12.  It has internal memory (1 kwords instruction,
512 words data,  24 and 16 bits wide respectively), and
boots instruction memory off of an eeprom.  Minimum setup
would probably be ADSP2105, xtal, eeprom (4k), max232 
(interface voltage levels), DAC/ADC chip and a power supply.

You can reach Analog Devices at (617) 329-4700,  they
send out spec sheets for free.

> --
> Regards,
> Uri         uri@watson.ibm.com      scifi!angmar!uri 	N2RIU
> -----------
> <Disclamer>
> 
>