From: Ray Cromwell <rjc@clark.net>
Date: Sun, 13 Aug 95 01:29:18 PDT
To: eb@comsec.com (Eric Blossom)
Subject: Re: PRZ encrypted voice software release imminent
In-Reply-To: <199508112143.OAA02837@comsec.com>
Message-ID: <199508130829.EAA04681@clark.net>
MIME-Version: 1.0
Content-Type: text/plain



[stuff about tuning algorithm to channel characteristics]
> 
> None of this says that you shouldn't also optimize for the packetized
> case too.  I think that you can negotiate the right behavior at start
> up time based on detected channel characteristics.  I think that the
> biggest impact is in the framing overhead, or lack of it.
> 
> You are always trading off bandwidth, speech quality and MIPs.

 I agree with this, but it is still possible to do all this through
an abstract interface layer. One can "query the line characteristics"
of a transmission layer and then limit the selection of algorithms
based on those characteristics.

Example: we have a class TransmissionLayer, and two derived
classes "syncrhonouslayer" and "asynchronouslayer" (subclass as
appropriate). Note, no underlying link type is being refered
to.  It could be a network or a modem.

Now we have a bunch of algorithms (codecs), CodecA is optimized for
a synchronouslayer with atleast 16kpbs. CodecB for asynchronous
packet networks.

At the application layer, the user chooses a way of connecting.
The application instantly picks the best codec (supported
by both ends) for that transmissionlayer. it alo updates the user
interface automatically, e.g. displaying a "half duplex"
mode for one type of link, or "conference call' for another.
Some types might not support all encryption types
because of cpu limits (also detected)  There's no reason
this could not be programmed. It would also be highly portable,
highly maintainable, and more easily adoptable.

Direct-to-hardware hardwired algorithm software is good for
proof of concept. But I'm thinking ahead, to a time when
a multimedia protocol will be just another transport layer ontop of
which cool applications are running. (like http+mime runs over
TCp)

-Ray