From: gerg@netcom.com (Greg Andrews)
Subject: Re: Slow Worldblazer to Worldblazer uucp transfers
Organization: Netcom Online Communications Services (408-241-9760 login: guest)
Date: Thu, 1 Oct 1992 08:27:47 GMT

In article <1992Sep28.181534.6709@ssw.de> root@ssw.de (Benno Lange) writes:
>
>We did some tests between two machines during the weekend using 2 WBs.
>One was hooked up to a 486/33 w 16550 + SVR4 + FAS + HDB-uucp,
>the other one to a MOTOROLA Delta 68040 w SVR3 + taylor-uucp 1.04.
>Both machines and modems have HW handshake, spoofing and
>V42bis data compression enabled. Both WBs have LA5.00W ROMs.
>
>We had previously used an interface speed of 19.2kbps and got a
>xfer-rate between 1600 and 1750 bytes/sec on compressed news batches.
>(as reported in xferstats of uucp)
>

1750 cps is normal for a 64-byte packet uucp session that's saturated the 
19200 bps port speed.  1920 * .914 = 1755 cps.

>
>Switching to 38.4kbps resulted in a xfer-rate between 1950 and 2040 bytes/sec.
>Increasing the interface speed to 115.2kbps did NOT increase the xfer-rate
>any further.
>

Well, of course.  You were transferring COMPRESSED data, so the modem's
V.42bis compression couldn't boost your throughput.

>
>The rate of ~2000 bytes/sec seems to be a bit low if I see other people
>measuring xfer-rates of ~2200 bytes/sec ?
>What have we done wrong ?
>

Can't tell.  If the modems can achieve full speed, they can give you
2300 cps throughput.  The resulting uucp throughput would be around
2300 * .914 = 2102 cps.

One of the first questions I would ask is whether the modems were able
to achieve full speed over the phone line.

>
>Checking the modulation rate registers show even values well above 23kbps:
>    s70 ~24000      s72 ~26500
>

The S70 register is showing a little slower than S72.  Each register shows
a direction, one for receiving, the other for transmitting.  Perhaps your
transfers were in the slower direction.  When the modem's raw transmission
rate is slowed, the data throughput will also be slowed.

>
>(I don't know what 'modulation rate' really means. But I think that they
>give a measure of the real xfer-rate on the line. Greg could you shed some
>light on this ?)
>

PEP is different from other modem modulations.  The raw bit rate shown
in S70/S72 will be HIGHER than the data throughput.  The raw bit rate
is how fast the modems are really transmitting to each other.  The data
throughput is reduced because of overhead from the error control protocol
and line turnarounds to acknowledge the data packets.

>
>IMHO the 70kbps mentioned in the WB manual seems to be only the data rate
>between modem and computer and NOT between modem and modem !!
>

No, the data throughput can reach those speeds, under the circumstances
that you outline in your next sentence:

>
>The interface speeds higher than 38.4kbps seem only to be good for sending
>mostly UNCOMPRESSED data.
>(tests with a compressable file show xfer-rates of ~3300 bytes/sec @ 115.2kbps)
>

Well, of course.  The modem's throughput without compression is about
23,000 bps (depending on line conditions), and the throughput with
compression can be up to 70,000 bps - provided the files can be
compressed by the modem!

There's nothing new about this.  V.32bis modems claim data throughputs
of 16,000-17,000 bps (1600-1700 cps) without compression, and up to
57,600 bps (5760 cps) with V.42bis compression.  For Turbo-PEP it's
23,000 and up to 70,000.


-- 
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