🚀 go-pugleaf

spaz@chocks.com (sPONiX) wrote:

> On Sun, 29 Aug 2004 21:48:28 +0100, =?UTF-8?B?UGFsaW5kcuKYu21l?=
> <sb382638@hotmail.com.invalid> wrote:
> 
> >Compression does not allow more information bits to be sent 
> >down the line 
> 
> Eh?

What our palindromic friend meant was that there's no technology that'll
improve your absolute bitrate from V90/V92/whatever the modem's set to.

All that you can achieve is to increase the effective bitrate (not the
same thing) by using compression at both ends of the connection.

The data-theoretic term is "entropy" -- a data-stream's entropic when it
can be compressed no further without loss of information: when the
encoded data are infinitely close to pure random in nature.

The thing is, data created by current image and multimedia compression
techniques are moderately entropic already: you can't get them much
smaller without losing (yet more) information: in other words, degrading
the content they're encoding.

If you're mostly transferring text data, for example email and Usenet
messages, or non-image-containing Web pages, there's a lot you can do
with compression.  The simple fact is, though, that most 'net users
spend most of their time transferring fairly entropic data, so
compression won't gain them much additional benefit.

There is another way you can pretend to achieve higher bitrate, and
that's by spidering content: when you download a Web page, you also
start downloading and caching everything it links to (and maybe even
everything those pages link to).  Needless to say, this is pretty
antisocial, since you'll be downloading maybe 10-20 times more data per
page than you actually want, on the off-chance that you might click on a
link.  Some ISPs really, *really* don't like spidering.

One more thing, whilst I'm thinking about it.  Remember that I was
talking about end-to-end compression?  To make that work, the head-end
has to compress the data being sent to you -- and that's not at your
ISP, that's at the scam^Woops, "free" affiliate-promoted service's
premises.  To do that, they have to have some pretty hefty servers
(since the server CPU usage in compressing the data will be
substantial), and presumably a fairly fat pipe to the Internet.

How can they afford to provide this, for a "free" service?  How can they
afford to pay the affiliates to promote this "free" service?  Food for
thought, no?


Jon
(whose degree thesis was on data compression, by the way)
-- 
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