High-Speed Modems for the Atari ST: Summaries

High-Speed Modems for the Atari ST: Summaries

Post by Bryan Jones Woodwor » Thu, 21 Jun 1990 06:57:40

Thank you all for your submissions to my mailbox!  They were very informative
and [in a few cases] nicely blunt!

It seems the U.S. Robotics ninety-six hundred HST is the best modem available
for the ST.  Most ST bbses supporting higher baud rates use the HST by U.S.
Robotics.  I have seen the price range from as low as $4oo to as high as
seven-hundred, depending on where you shop.

And now, the summaries.  Thanks once more.


Most 19.2K bps modems do support all the lower speeds.  The better ones,
when hooked to a modem of the same type actually sample the line for the
fastest possible error-free transfer.  

As far as speed comparisions, the transfer protocol you use has a large
effect as does the line quality.  But the difference in time should approach
the difference in baud (e.g. 9600 is 4x as fast as 2400).

Us Robotics sells a good 9600 bps modem for the ST.  You used to be able to
get it cheap if you were a sysop.  I dont know about 19.2 K or higher for
the ST, although, like you, I know its available.  Unless its self-correcting
as mentioned above, I believe line noise would be a problem frequenly.
From: David Forster

A recent (June, even?) issue of Computer Shopper had a section on buying
modems, which I found fairly informative.  The upshot of it is:  2400 baud
modems are generally interchangeable, but check them out when you get them,
because tolerances are sometimes very tight (an office mate had to return
his brand-new modem because it wouldn't work with our local phone system and
the modems our machines use, but another user here has had his running for a
while, and finds it more reliable than his old 1200 baud modem was).
Once you get up to 4.8k, you get into the realm of shifting (or non-existent)
standards.  A number of cheap 4.8k modems are cheap because they won't work
with a wide range of equipment on the other end.  (In our case, they wouldn't
work at all, since we don't have any 4.8k modems!)  I don't know when standards
will finally be established, but I expect it won't be too long.

Anyway, don't take my word for it (this is all from memory, anyway), go out and
get a copy of the magazine, if you can.

In Norway we don't use the HST standard but CCITT V.32  (9600 MNP5)
Most BBS'es offer this standard now (including my own) and some even
offers both V.32 (9600) and HST (14.4K) speeds.....
From: sun!usc.edu!baffoni%alcor.usc.edu (Juxtaposer)

Actually, I have used my 2400bps modem to transfer stuff at an average
of 230 bytes/sec.  I think this works out to be under a meg/hour:720k/230=52
minutes.  However this is with little or no line noise and this is using
y-modem with 1k packets.  I could get a slightly higher throughput if I used
something like zmodem which, if it has the proper emulation, will transfer a
continuous stream and only send acknowledgements and bad blocks at the end.  
Also you must consider the increasing amount of noise that gets into transmis-
sion as you creep up the speed scale so, even though I get 230 cps with a
2400bps modem, it does not neccessarily mean you will get 920cps with a
9600 bps modem.  

Hope this helped.

Hi Bryan,

I read your question about modem speeds. It is not exactly what you asked
for but maybe it helps you:

The biggest files I send were about 200k. I send these files several times
and the time to transfer them was nearly constant. I used ZMODEM on good
lines, so 1024 bytes blocks were used.
I use a 1200 baud modem.
I get a throughput of 103 - 104 characters per second.

This means that 10k will cost 99.5 seconds.

So 2400 baud 10k should be 49.7,
            720k should be 3579 seconds = 59 minutes and 40 seconds.

using XMODEM I get a throughput of nearly 90 characters per second.

Hope this will help you,


Quote:> All of the replies were very good, however no one mentioned how FAST the
> high-speed modems transfer data over
> a computer.  

> All one must do is supply me with the following data:  How long does it take
> a 24oo baud modem to transfer a whole
> Atari ST seven-hundred and twenty-K diskette over the modem?  Then, I can
> convert this data for the other modems and determine which speed is for me.

Well, why don't you figure out that by yourself?

It's quite easy: 2400 baud actually means 2400 bit/sec.
An 8 bit-byte is transferred as 10 bits, since there
is are additional start- and stopbits.
In theory, you get the following:
        2400 baud = 240 byte/sec =  14.400 byte/min
If you want to transfer 740.000 bytes it'll take you
        740.000 byte / 14.400  byte/min = 50 min

But that's theory. In practice, you need a protocol (kermit, xmodem, ...)
to insure that your data is transmitted correctly.
These protocols do a handshake after each tranmitted block and thus
decrease your transmittion rate enormously.
Depending on the protocol, you get only 50 to 70% of the
original transmittion rate.
And this decreases further if you are on a bad phone line.
Such a bad line causes transmittion errors which, in return, cause
a retransmittion of the erroneus blocks.

Furthermore you have to take into account that higher transmittion
rates require better line quality, i.e. you will get more transmittion
errors using higher baud rates, thus increasing the need for retransmittions.

Concerning the 720K of a disk: you can try to compress them for
transmittion. The compression ratio depends on the type of compression
and the tye of data. Highest compression ratios you get on ASCII-Texts.
Some tools (UNIX-compress or LHARC) can compress ASCII-Texts down
to than 30% of the original size.
Compression on progam binaries is not so good, a good compression can acheive
60 to 80% of the original size.

Some modems support a compression themselves (MNP5 e.g.).
This compression is not very effective and is - in general - only
effective on ASCII-Texts.

Quote:> I want to insure that I get a modem which is neither too slow, nor too much
> for my needs.  I have seen BBSes in
> my area [San Jose, CA] supporting baud rates close to 2OK!  [Nin*.2K to
> be exact].

By the way, the PEP mode (which is the one that is always used if
you want to communicate at 19k2   d o e s   a l r e a d y   include
a special transmittion protocol, which decreases the actual transmittion
rate down to about 15k, depending on the phone line)


Hope this is what you wanted to know.

Thinking back to my old PCP days....

Large arcs could take 40-50 minutes, depending on how many retranmissions
were made, at 2400 bps.  Large arcs were in the area of 600K, so an hour
per 720K  isn't probably too far off.

My only concern is whether or not I was at 2400 then.  Those may be figures
for 1200.  Hmm....

The above was using YMODEM or XMODEM 1K protocols.  Zmodem or SEAlink would
be faster is the line quality was good.

Ill see if I can find out more....


Former Handle - The Computer Kidd, Sysop of the Electronic Buccaneer,
                Eatontown, NJ (Atari 8-bit bbs)


1. High-speed modems and the Atari ST

Having just recently acquired an USR Courier HST Dual Standard, I am anxious
to compare notes with other ST users who favor the USR high speed modems,
especially in the area of throughput.

I am currently getting about ~1625 cps in HST mode.  Protocal used is Zmodem
and I have the comm port locked to 19200 with TURBOCTS installed.  The USR
manual says that I should be getting 1740 cps while in HST mode.  So where
is the missing ~100 cps?

Also, is there terminal software out there which supports Ymodem-G?  I
noticed that on uploads, my throughput drops way down to ~600 cps.  So I
want to see if using Ymodem-G instead of Zmodem will kick that cps rating up
a little bit.

Please mail any replies.  Thanks.

           Henry Kwan - FWB, Inc.         |  "Experience varies directly

  {claris,ucsfcca,hoptoad,lamc}!wet!logic |              -- Tech Support

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