[167] in linux-net channel archive
Re: PPP and VJ compression problem
daemon@ATHENA.MIT.EDU (Michael Brennen)
Wed Mar 29 18:21:49 1995
Date: Wed, 29 Mar 1995 08:22:28 -0600 (CST)
From: Michael Brennen <mbrennen@fni.com>
To: Bob Doolittle - Sun Parallel Open Systems <rad@via.East.Sun.COM>
cc: linux-ppp@vger.rutgers.edu, linux-net@vger.rutgers.edu
In-Reply-To: <9503281904.AA00499@via.East.Sun.COM>
On Tue, 28 Mar 1995, Bob Doolittle - Sun Parallel Open Systems wrote:
> I would suspect that you probably lose more bandwidth by totally
> turning off the asyncmap than you lose by turning off the VJ protocol.
> Statistically speaking, completely turning off the asyncmap should eat
> 13% of your bandwidth off the top (ctl chars = 25% of ASCII chars,
> escaping these halves your bandwidth). Typically you really only need
> to escape about 4 characters, which would eat only 2% of your
> bandwidth. Do you know the specifics of what VJ compression buys you?
> I know with no compression at all, a TCP/IP header is 40 bytes, but I
> don't know how small this gets after the other compressions (non-VJ)
> are performed, nor do I know how big a VJ header is. Any data would be
> welcome.
> Isn't there some way of determining automatically what maximal
> asyncmap can be used safely over your link? Other similar serial-line
> protocols do this (e.g. term). In fact, you could probably use these
> tools to determine your best asyncmap for PPP (it might be a slight
> superset, but better than 00000000)!
My understanding was that 'asyncmap 00000000' *disabled* escaping
characters - i.e., a map of zero meant greater bandwidth. Did I miss
something from the man page description?
Michael
