From: Eric Blossom <eb@comsec.com>
Date: Wed, 16 Aug 95 12:58:03 PDT
To: die@die.com
Subject: Purple Boxes
In-Reply-To: <9508160230.AA01456@pig.die.com>
Message-ID: <199508161935.MAA23741@comsec.com>
MIME-Version: 1.0
Content-Type: text/plain


>	I reiterate my suggestion of a few months ago that
> one could quite easily adapt the firmware on one of the new simultanious
> data and digital voice on the same phone line modems to incorperate
> encryption, and quite possibly encryption/key exhange interoperable
> with some mode of PGPphone. 

I've looked at the AT&T simultaneous voice and data stuff (VoiceSpan),
and from what I can determine from reading between the lines, the
voice stuff is not really digitized (a la PCM), rather it is just
pushed around somewhere else in the spectrum.  The data is apparently
modulated using a variant on QAM, and the data rate varies dynamically
depending on whether or not you are saying anything.

As I recall the block diagram is ...

				+-----------+	    +--------+
             analog voice <---> |           |  	    | 	     |<--- TIP
			        | Modem IC  |<----> |  DAA   |
	digital bitstream <--->	|           |	    |        |<--- RING
				+-----------+	    +--------+


You can get data sheets from AT&T Microelectronics.

Eric