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From: garyf@mc0.UUCP (gary friedman)
Newsgroups: net.unix-wizards
Subject: Re: simultaneous file transfer on ethernet (SUN's)
Message-ID: <335@mc0.UUCP>
Date: Fri, 5-Sep-86 13:28:47 EDT
Article-I.D.: mc0.335
Posted: Fri Sep  5 13:28:47 1986
Date-Received: Mon, 8-Sep-86 00:16:04 EDT
References: <6@cvbnet.uucp>
Reply-To: garyf@mc0.UUCP (Gary Friedman)
Organization: Jet Propulsion Laboratory, Pasadena, CA
Lines: 43

In article <6@cvbnet.uucp> acrotty@cvbnet.uucp (Art Crotty) writes:
>
>I would like to have the ability to transfer large application
>programs to all nodes on the network simultaneously.

The short answer to your question is you *can* broadcast your updated
programs to your other nodes, but you shouldn't.  The reason for this
will take some explaining. 
	The Ethernet protocol you said you had, TCP/IP/UDP, are
actually 2 seperate protocols that can co-exist harmoniously: TCP/IP,
which will guarantee packet delivery to one node only, and UDP, which
guarantees nothing.  One of UDP's features is, since it transmits
packets without waiting for any kind of acknowledgement, it is able to
send to a special broadcast address and have 'billions and billions'
of machines (which are also set to receive with this same broadcast
address) receive them without the overwhelming overhead that would
otherwise be required in such a case.  Many erroneously equate "UDP"
with "Broadcast", when in fact "Broadcast" is merely a special case.
	As you can probablly guess, if you choose to broadcast your
updates to all your Sun workstations, you run the risk of randomly 
dropping packets or losing bits of information in other ways.  This
risk is even greater if the other Suns are transmitting information to
each other (Using TCP/IP, no doubt) in the background at the same
time.  An example: In my studies of UDP reliablilty, it was common for
a Sun3 to send 100 UDP packets and have a Sun2 receive only 65 of
them.  (This result is amplified by the fact that the Sun3 sends them
faster than the Sun2 can physically receive them.  Sun2 to Sun2
generally yields better than 98% of the message when lots of other
Ethernet activity is taking place.)
	My reccommendation is to use NFS, as it was designed for
precisely your situation.  (The original posting didn't state why the
option was ruled out.)  If that option isn't acceptable, the next best
option is to write a shell that sequentially rcp's the file to every
node individually.  (RCP uses the TCP/IP protocol; it's no dummy!)
	Sorry about that---and good luck.


-- 

Gary Friedman
Jet Propulsion Laboratory
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