> Date: Wed, 28 Apr 1999 14:26:40 +0000
> From: Julian Munoz Dominguez <[EMAIL PROTECTED]>
> Subject: Re: Compression in packet radio
> [...]
> AX25 is not prepared to support compression. Because compression "needs"
> a kind of negotiation. Brian ko4ks and Thomas A. Moulton W2VY (Uhm, not
> sure it was him) have done a study about that. The solution was to modify
> a bit the ax25 protocol, using reserved bit for negotiation purposes.
> [...]
The AX.25 [Version 2.2] XID frame provides a mechanism for negotiating
parameters. This seems like an ideal (perhaps even obvious) mechanism
for negotiating AX.25-level compression.
> Well, I think the better solution is to put an intermediate compression
> layer, just on the top of ax25. That is, some of the ax25 saps (= some
> of one of our callsigns+ssid) can be connected to this layer. All that
> using precedent studies, sure.
> [...]
> Or even better, the compression layer could be called by the kernel when
> the client uses some predefined ax25 callsigns (callsigns that we want
> to use to connect to ax25 peers using compression), for example
> translating the systems calls in system calls for the compression layer.
I generally dislike overloading AX.25 callsigns, because it easily leads
to a mess. If this callsign overloading is configured by hand, then
this is one more human operation that needs coordination, is likely to
introduce errors, and is likely to be difficult to debug if things
are mis-configured.
Overloading AX.25 callsigns is not very extensible. As soon as you
want to negotiate more than one parameter at a time using [overloaded]
callsigns, you start having difficulties, (such as an explosion of
special callsigns).
I also believe that trying to use callsigns for parameter negotiation will
quickly conflict with the primary use of callsigns, namely to route
stuff.
-tjs
