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From: davids@iscuva.UUCP (David Schmidt)
Newsgroups: net.sources.d
Subject: Re: \"FAST\" protocol proposal from Hayes
Message-ID: 
Date: Thu, 14-Aug-86 12:26:26 EDT
Article-I.D.: iscuva.247
Posted: Thu Aug 14 12:26:26 1986
Date-Received: Sun, 17-Aug-86 05:31:54 EDT
References:  
Reply-To: davids@iscuva.UUCP (David Schmidt)
Organization: ISC Systems Corporation, Spokane, Wa.
Lines: 40
Keywords: errors reliability end-to-end CRC

In article  campbell@maynard.UUCP (Larry Campbell) writes:
>In article  W8SDZ@SIMTEL20.ARPA (Keith Petersen) writes:
>>D.C. Hayes (the modem people) are proposing a new protocol...
>
>>Fast is a session-level file transfer protocol designed to run over an
>>error-free link such as X.25, X.PC or MNP.  Since the link is assumed to be
>>error-free and packetizing is done by the network layer of the underlying
>>protocol, no error detection/correction mechanisms are necessary.
>
>What an irresponsible statement!  Sure, the link from modem to modem
>may be relatively error-free, but what about the links from computer to
>modem on each end?  Who checks them?  Doing file transfers without
>end-to-end error checking is simply a subtle way to play Russian
>roulette.  Responsible software engineers will avoid this protocol
>like the plague.

If you read the documentation carefully you will see that the FAST
protocal does include the capability of using a CCITT CRC-16 check
on the file sent.  If this is uses (I wouldn't use FAST without it!)
then you do have an error-free protocal.

The only difference between FAST and KERMIT or XMODEM is that the
"packet size" is indefinite (the full size of the file) instead of
a fixed size.  Also it is not clear to me if the file is automatically
re-sent or if the recieved file is deleted (with an error message of
course).

It remains to be seen how often errors will occur.  If I only have
to re-send one file out of 100 for instance,  I can save quite a bit
of time overall if each file transfers twice as fast (Telenet and 
Tymnet transfers are SLOW!).
-- 

+----------------+
! II      CCCCCC !  David Schmidt
! II  SSSSCC     !  ISC Systems Corp.
! II      CC     !  Spokane, WA
! IISSSS  CC     !  UUCP: ihnp4!tektronix!reed!iscuva!davids
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