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From: jbn@wdl1.UUCP
Newsgroups: net.micro
Subject: Re: What is Tymnet?
Message-ID: <690@wdl1.UUCP>
Date: Thu, 5-Sep-85 21:23:24 EDT
Article-I.D.: wdl1.690
Posted: Thu Sep  5 21:23:24 1985
Date-Received: Mon, 9-Sep-85 02:14:09 EDT
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Organization: Ford Aerospace, Western Development Laboratories
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Nf-From: wdl1!jbn    Sep  5 13:28:00 1985


     Tymnet is the first large packet switching network; it came up slightly
before the ARPANET in the late 1960s, as a system used to allow customers 
to access the time sharing computers of Tymshare, Incorporated.  As 
deregulation of telecommunications began, the network was offered as a service 
to other operators of computer systems, and the business was split off as 
Tymnet, Incorporated.
     The original Tymshare hosts were Scientific Data Systems 945 machines;
the original packet switches were Varian Data 620Is.  Tymnet was and is
a virtual circuit network with central call setup and teardown.  There is
a central network supervisor that sets up and tears down connections,
authenticates users, and records accounting information.  There are several
machines throughout the net that can be the supervisor, but only one is
active at any one time.  (In recent years, the network has grown to the
point that there are now regional supervisors, but the centralized control
concept remains.)  The original network backbone was only 2400 baud, but
this has been increased substantially over the years.
     All virtual circuit networks are in a sense descendants of Tymnet;
the X.25 link / X.75 gateway model of the world is close to the Tymnet
design.  The original Tymnet papers make fascinating reading today; the
terminology of ``red balls,'' ``green balls'', ``circuit zappers'', and
``leprechauns'' seems very strange today.  But someone had to invent the
technology, and they did it.  Tymnet is definitely not based on the
ARPANET; in fact, Telenet, which started with ARPANET technology, has
converted over to a system more like Tymnet.
     Tymnet today has dial-in ports in most major population centers
of the U.S.; their primary business is offfering dial-in access over a
wide area for terminal to host communications.

					John Nagle