BG> Quite so, and in fact, these fake test files full of Xs are
BG> the worst possible example to use.  Sure, they compress better
BG> than anything else under BTLZ (something you'd never see in the
BG> real world anyway, as you know), but the real shock comes when
BG> you PRE-compress such a file before sending.  Tried it myself
BG> once, and a 100Kb file of Xs Zipped down to less than 1Kb!

RS> Yeah, the BTLZ is fundamentally crippled by the fact
RS> that it only sees quite small chunks of the file at
RS> a time. So it does very badly even on those files compared
RS> with a standalone archiver which can analyse the whole file.

BG> Exactly.  The default BTLZ dictionary size in most modems is just
BG> 2048b, only 2K of data being analysed and compressed at any given time.

Well, this bit is a tad mangled. The dictionary size isnt the size
of the chunks of file being processed, its the size of the dictionary.
And a file of Xs isnt using dictionary style compression anyway, its
just replacing a string of Xs with a 'here come 200Xs' type compression.

BG> Mind you, some makers like Hayes have defaulted to 8K BTLZ
BG> dictionaries, but all this seems to do so far is fuck up the
BG> negotiation phase of most other modems which don't support
BG> that size. Causes XID negotiation errors and a dropped DTR.

Yeah, there is a sense in which its a tad too complicated with the
unusual stuff. If you uses some of the more exotic variations you
might well find that some of the modems out there in the field have
some problems in their implementation of them which can bite you.

BG> So at say 3:1 compression in the modem, it transmits in around
BG> 20 seconds, but if compressed first, it reaches the other end
BG> in under 1 second! Why anybody bothers with uncompressed data
BG> is beyond me, except for relatively small (say <100Kb) files.

RS> The main situation where it can be handy is with stupids
RS> who will stuff it up if they have to archive it first.

BG> Is there anybody still that stupid these days though?

Yeah, plenty of them out there. Its easy for us to forget that
most of the droids out there dont even know what an archiver is.

Thats one advantage of the approach MS has taken with fax support
with WFWG. You basically just tell the system to send it, by the
fax appearing as another printer. And if it discovers its got WFWG
at the other end of the call it will even send the file in binary
format over the link, not as a fax at all. Rather elegant in some ways.

RS> Particularly if they dont actually pay for the connect time, coz
RS> its a local call. Can be operationally convenient in that situation.

BG> Sure, BG comms with local calls are irrelevant time-wise, I suppose.

Yeah, and they are still the bulk of the calls for most people.

BG> Marginally better than 3:1 measured here, but Paul will
BG> never see anything like this much compression in real life,
BG> and like you, I simply cannot see any purpose in locking
BG> the port at any more than twice the modem's highest available
BG> link rate (57600 in my case, 38400 in yours and Paul's).

RS> Its actually a fascinating commentary on human nature, it really
RS> is quite amazing the sorts of people who cant really grasp it.

BG> Like that Arthur fellow in Aust_Point (who disappeared with his
BG> tail between his legs when his stupid errors were pointed out).
BG> Not even the courtesy of a reply, or a "sorry, you're right
BG> after all". What a wanker.  Must be off having his SOH repaired.  |-)

It way actually young Johnny Davidson. Back yesterday for more snide
remarks |-)

RS> Essentially what they are doing is not really grasping the engineering
RS> and they just use their gut reaction instead, and its wrong. You see a
RS> similar thing with simple stats, people say 'my BIL had a holden and
RS> the engine fell out' as if that proves a damned thing about reliability.

BG> Yep, and you see the same thing with Lewin and his Rockwell zealot mates.

Yeah, havent seen such florid conspiracy theory stuff for quite a while.

RS> Still, we are getting better, not too many people sacrificed their
RS> children to the gods to make the drought go away this time around.

BG> Wish Russell's parents had sacrificed him though. Not too late is it? |-)

Yeah, still havent quite worked out what flavor of FRZ they are.

--- PQWK202