Path: utzoo!utgpu!attcan!uunet!auspex!guy
From: guy@auspex.UUCP (Guy Harris)
Newsgroups: comp.dcom.modems
Subject: Re: UUCP g stats
Message-ID: <412@auspex.UUCP>
Date: 7 Nov 88 20:44:44 GMT
References: <184@arnold.UUCP> <1892@van-bc.UUCP> <2032@udccvax1.acs.udel.EDU> <331@auspex.UUCP> <762@wsccs.UUCP>
Reply-To: guy@auspex.UUCP (Guy Harris)
Organization: Auspex Systems, Santa Clara
Lines: 41

>But the synchronus connection is what buys you such a high data rate in the
>first place... the multi-carrier modulation used by Telebit requires it by
>virtue of their encapsulation method.

You're *still* missing the point.  The high data rate doesn't buy you
anything in terms of raw throughput *unless you can get the bits to the
modem that fast*.

>The compression on the TB buys you exactly what you are saying it can't buy
>you... putting characters in one modem and pulling them out another at a
>higher rate than the modulation method used can push bits.

Excuse me, but I didn't say it wouldn't buy you that.  What I said was
that it couldn't get the characters *from end-to-end* - that is, from
*host* to *host* - faster than you can get the characters from the host
to the modem.

>By incorporating compression encapsulation into a transfer protocol, and
>using this protocol to transfer files, you CAN put more bits through the
>serial port than the machine is capable of.

If you do the compression in the modem, it only increases the speed of
the modem-to-modem connection - which helps only if you can get stuff
into the modem at that speed.

If you do the compression in the host, you can think of it as a way to
increase the speed that you can pump data into the modem - but this has
nothing to do with the speed of the modem.

>I STANDARDLY do this daily, getting an average of 40% compression at
>9600 between my DOS, my Xenix, and the VMS and Ultrix machines I have
>access to.  My effective baud rate is 9600 * 1.4 = 13340.

That's nice.  Try getting that effective baud rate if your modem can't
handle data coming into it *from the host* at 9600 baud.

Chris's point still stands; if you have modems that, complete with
compression and other tricks, can send 1 GB of data over the wire, but
the modems can only receive data from the host at 9600 baud, you're
going to get an effective baud rate no better than 9600 baud times
whatever compression factor you get from host software.