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From: "Igor Sysoev" <igor@nitek.ru>
To: <freebsd-questions@FreeBSD.ORG>, <robert@chalmers.com.au>
Subject: Re: Turning off VJ compression. Is it necessary
Date: Fri, 29 Jan 1999 11:15:23 +0300
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> From: Robert Chalmers <robert@chalmers.com.au>
> Subject: Turning off VJ compression. Is it necessary
> 
> I see from the archives that if modem compression is turned off, then VJ
> compression operates more efficiently. Among other things..
> quote:............
> 3. Modem compression, as you have noticed, often interferes with VJ
>    compression used in SLIP and PPP implementations.

I don't think so.

> 2. Modem compression often interferes with, and lengthens transfer of,
>    compressed files such as .gz and .jpg.

Yes, it's true. But besides compressed files there are HTML, mail, news.
They have good compressed rates even with v.42bis.

> 1. Modem compression slows down turn-around time -- terrible for
>    interactive sessions.

As far as I know turn-around time slowed by v.42 because it uses
blocks to transfer. Modem compression's impact is minor here.

> pppctl indicates that VJ Compression is on, on the ppp link, although I
know I
> turned compression off in the modem (%C0 - Hayes Accura).
> 
> But, is there any improvement in turning off VJ Compression as well, or
is it
> better left on?

You better left VJ. In my ppp connection it reduces TCP/IP headers of
60%-100% packets from 40 bytes to 3-16 bytes.

Igor Sysoev


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