On Tue, Apr 27, 1999 at 03:56:49PM +0200, Jonathan NAYLOR wrote:
> > I've watched the discussion about the need for compression to be added
> > to the various services run over packet radio. Why is everyone so
> > intent on modifying *every* service individually? What we need is to
> > have the ax.25 protocol layer negotiate compression on connect.
>
> .... and there is the problem. If the mapping was one-to-one between AX.25
> connections and services then we would possibly be OK. But a single AX.25
> connection can carry many things, not just user-to-user data, for example
> multiple NET/ROM, ROSE and TCP/IP sessions.
Which is exactly the reason I think compression at the ax.25 level is the
place to put it. Then every packet transmitted could (but does not have
to) be compressed. We have compression available in slip, and ppp why not
expand it to ax.25.
>
> The second point is to do with the efficiency of compression. To get good
> compression you need a reasonable amount of data and that means having access
> to (for example) the complete BBS message before transmission. This then means that
> we would have problems if we negotiated compression at each hop instead of end
> to end.
To get the most out of compression you need to compress the entire item at once.
As soon as a machine starts using an application that does not do compression,
you loose channel capacity (in terms of maximum uncompressed data flow) since the
station(s) transmitting data from the application will require more packets to
send the same data. Why no allow for ax.25 level compression of the payload,
provided it decreases the size of the payload data (sometimes compression of
compressed data expands the size of the "compressed" data), and promote the use
of compression in application level protocols.
This way if an application provides compression the data transmitted is minimized,
and if the application does not support compression the network protocol will
kick in and provide *some* benefit of a less than ideal compression.
> Put it where it belongs, and that is with the service, just above the socket
> layer. That implies a library and of course some form of system to negotiate
> the use of compression anyway, which is usually service specific.
Provided you can get the service to be modified to support compression.....
I really think we need both.
> > Is fearr Gaeilge bhriste, n� B�arla cliste.
>
> What language is this ?
Irish (Broken Irish is better than clever English :-) )
Pat
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Is fearr Gaeilge bhriste, n� B�arla cliste.
