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From: mmcnew@pro-freedom.cts.COM (Monty McNew)
Newsgroups: comp.sys.apple
Subject: Transfer protocols
Message-ID: <8809210141.AA02974@crash.cts.com>
Date: 19 Sep 88 22:36:57 GMT
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Gynn@smoke writes:

>At normal modem speeds such as 2400 bps, there is so little gain
>in switching to a streaming protocol as to make it a waste of time
>to implement.  Do the calculations..

Streaming protocols can and do make a difference in file transfer times.  If
it is a direct connection (LD, Local calls etc) the difference is worth the
effort.

This months GEnie Livewire magazine (page 20, not talking about Y-modem G
though, but xmodem 1k) says:

"XMODEM (1k blocks) is a variation of the original XMODEM.  The only
difference is that the file is broken into 1,024 byte blocks (instead of 128
bytes for original XMODEM blocks).  The major advantage of this is that the
error checking is performed only once every 1,024 bytes.  Less time is spent
with error checking, reducing download time."

It goes on to say:

"Out tests show that XMODEM 1k and YMODEM downloads are about 5-10% faster
than standard XMODEM."

Article also points out that there is a caveat if there is an error in a
block that you also have longer time re-sending since the blocks are larger.

Where a streaming protocol _REALLY_ is beneficial (although XMODEM 1k or
YMODEM is not streaming really) is while using PC Pursuit.  If you have ever
tried a 1200 baud XMODEM d/l over PC Pursuit, you soon realize that it takes
a little over twice as long than if you were calling direct.  Using YMODEM
over a service such as this greatly reduces this time by about 35% (although
I have not actually calculated it).  Some BBS's won't even let you do an
XMODEM d/l if you are calling via PCP, they delete your account if they catch
you doing it.

I understand (although I have not tried it) that ZMODEM over PC Pursuit is
almost as fast a file transfer as if you were calling directly to the system.

Someone else out there can fill in why it takes so long to XMODEM over PC
Pursuit.  I don't know the exact reason, something about the error checking
over PCP's packet switching delays everything, hence the less error checking
the protocol does, the less time it takes.


I realize my two bits worth here have nothing to do with Y MODEM-G (I have
never seen this one) but the point is, any protocol that uses larger blocks,
creating less error checking time, is going to be faster.  Plain and simple. 
If you are using PC Pursuit, the time savings are well worth it, although
calling direct at 2400+ baud might not be, unless it is a very large file.

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