Xref: utzoo comp.dcom.modems:5337 biz.comp.telebit:39
Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!uunet!codonics!bret
From: bret@codonics.COM (Bret Orsburn)
Newsgroups: comp.dcom.modems,biz.comp.telebit
Subject: Re: poor uucp performance - help! (LONG)
Message-ID: <960@codonics.COM>
Date: 24 Feb 90 08:37:30 GMT
References: <125@cdss.UUCP> <1990Feb17.063412.18455@rancho.uucp> <959@codonics.COM> <21377@ditka.UUCP>
Followup-To: comp.dcom.modems
Organization: Codonics, Inc., Middleburg Heights, OH
Lines: 42

In article <21377@ditka.UUCP> kls@ditka.UUCP (Karl Swartz) writes:
>In article <959@codonics.COM> bret@codonics.COM (Bret Orsburn) writes:
>>In article <1990Feb17.063412.18455@rancho.uucp> rock@rancho.uucp (Rock Kent) writes:
>>>4.  Make sure that you have compression turned off.  You don't want to
>>>    be compressing already compressed news batches.
>
>>Surely, compression will be less effective the second time, but is there
>>any good reason to disable it?
>
>Compressing random binary data will often make a file larger since
>there are no patterns for the compression algorithm to eliminate,
>and assuming the algorithm does a good job (which it does) a file
>that has already been compressed will almost certainly grow since
>they now have the overhead of the compression tables in addition
>to the uncompressible data.

Makes sense to me.

I wasn't aware that the two compression algorithms (a) are very similar
(b) are nearly optimal (c) have significant overhead [tables]. I will
take your word that such is the case.

It would not be necessary to transmit a table if the class of data to be
compressed was agreed upon in advance by both parties. That would seem to
be a sound and sensible policy for a news feed, though not for a modem.

The only remaining question is: Why does the little bit of documentation
available on this subject incorrectly recommend using compression?

(That is a rhetorical question. ;-)

Thanks to all who responded.

(I thank you, my phone bill thanks you, the man who pays my phone bill thanks
 you,....)


-- 
-------------------
bret@codonics.com
uunet!codonics!bret
Bret Orsburn