Tymnet

Tymnet was an international data communications network developed and operated by Tymshare. It was based at the company’s headquarters in Cupertino, California. The network used packet-switching techniques, including statistical multiplexing, and connected host computers at companies, educational institutions, and government agencies through synchronous leased lines and programmable terminal interfaces.
The business consisted of a large public network that supported dial-up users and a private network that allowed government agencies and large companies to build their own dedicated networks. The private networks were often connected via gateways to the public network to reach locations not on the private network. Tymnet was also connected to dozens of international public gateways via Tymnet II protocol and other public networks in the United States and internationally via X.25/X.75 gateways.
As the Internet grew and became almost universally accessible in the late 1990s, the need for services such as Tymnet migrated to the Internet style connections, but still had some value in the Third World and for specific legacy roles. However the value of these links continued to decrease, and Tymnet shut down in 2004.

Network

Tymnet offered local dial-up modem access in most cities in the United States and to a limited degree in Canada, which preferred its own DATAPAC service.
Users would dial into Tymnet and then interact with a simple command-line interface to establish a connection with a remote system. Once connected, data was passed to and from the user as if connected directly to a modem on the distant system.
Tymnet was extensively used by large companies to provide dial-up services for their employees who were "on the road", as well as a gateway for users to connect to large online services such as CompuServe or The Source.

Organization and functionality

In its original implementation, the network supervisor contained most of the routing intelligence in the network. Unlike the TCP/IP protocol underlying the internet, Tymnet used a circuit switching layout which allowed the supervisors to be aware of every possible end-point. In its original incarnation, the users connected to nodes built using Varian minicomputers, then entered commands that were passed to the supervisor which ran on a XDS 940 host.
Circuits were character oriented and the network was oriented towards interactive character-by-character full-duplex communications circuits. The nodes handled character translation between various character sets, which were numerous at that time. This did have the side effect of making data transfers quite difficult, as bytes from the file would be invisibly "translated" without specific intervention on the part of the user.
Tymnet later developed their own custom hardware, the Tymnet Engine, which contained both nodes and a supervisor running on one of those nodes. As the network grew, the supervisor was in danger of being overloaded by the sheer number of nodes in the network, since the requirements for controlling the network took a great part of the supervisor's capacity.
Tymnet II was developed in response to this challenge. Tymnet II was developed to ameliorate the problems outlined above by off-loading some of the work-load from the supervisor and providing greater flexibility in the network by putting more intelligence into the node code. A Tymnet II node would set up its own "permuter tables", eliminating the need for the supervisor to keep copies of them, and had greater flexibility in handling its inter-node links. Data transfers were also possible via "auxiliary circuits".

History

Beginnings: Tymnet

was founded in 1964 as a time sharing company, selling computer time and software packages for users. It had two SDS/XDS 940 computers; access was via direct dial-up to the computers. In 1968, it purchased Dial Data, another time-sharing service bureau.
In 1968, Norm Hardy and LaRoy Tymes developed the idea of using remote sites with minicomputers to communicate with the mainframes. The minicomputers would serve as the network's nodes, running a program to route data. In November 1971, the first Tymnet Supervisor program became operational. Written in assembly code by LaRoy Tymes for the SDS 940, with architectural design contributions from Norman Hardy, the "Supervisor" was the beginning of the Tymnet network.
One instance of the supervisor would be running at all times and choose a path through the network for each new interactive session.
The Varian 620i was used for the TYMNET nodes. Initially, Tymshare and its direct customers were the network's only users. In February, 1972, the National Library of Medicine became the first non-Tymshare network customer with a toxicology data base on an IBM 360.
It soon became apparent that the SDS 940 could not keep up with the rapid growth of the network. In 1972, Joseph Rinde joined the Tymnet group and began porting the Supervisor code to the 32-bit Interdata 7/32, as the 8/32 was not yet ready. In 1973, the 8/32 became available, but the performance was disappointing and a crash-effort was made to develop a machine that could run Rinde's Supervisor.
In 1974, a second, more efficient version of the Supervisor software became operational. The new Tymnet "Engine" software was used on both the Supervisor machines and on the nodes. After the migration to the Tymnet Engine, they started developing Tymnet accounting and other support software on the PDP-10. Tymshare sold the Tymnet network software to TRW, who created their own private network, TRWNET.
Tymes and Rinde then developed "Tymnet II". Tymnet II ran in parallel with the original network, which continued to run on the Varian machines until it was phased out over a period of several years. Tymnet II's different method of constructing virtual circuits allowed for much better scalability.
In 1996, the third and final version of the Supervisor was written in C for a Sparc multiprocessor work station by Tymes and Romolo Raffo. Node code software was ported from the Tymnet Engine to a Sparc platform by Bill Soley. Up to 10 old-style Tymnet Engines were replaced by a single Sparc node in the network switching centers.

Tymnet, Inc. spun off

In about 1979, Tymnet Inc. was spun off from Tymshare Inc. to continue administration and operation of the Tymnet network and its VAN services. The network continued to grow, and customers who owned their own host computers and wanted access to them from remote sites became interested in connecting their computers to the network. This led to the foundation of Tymnet as a wholly owned subsidiary of Tymshare to run a public network as a common carrier within the United States. This allowed users to connect their host computers and terminals to the network, and use the computers from remote sites or sell time on their computers to other users of the network, with Tymnet charging them for the use of the network.
The network offered an email service called OnTyme.

Sold to McDonnell Douglas

McDonnell Douglas Tymshare
In 1984 Tymnet was bought by the McDonnell Douglas Corporation as part of the acquisition of Tymshare. The company was renamed McDonnell Douglas Tymshare, and began a major reorganization. A year later, McDonnell Douglas split Tymshare into several separate operating companies: MD Network Systems Company, MD Field Service Company, MD RCS, MD "xxx" and many more.. At this point, Tymnet had outlived its parent company Tymshare.
McDonnell Douglas acquired Microdata and created MD Information Systems Group, expecting to turn Microdata's desktop and server systems along with Tymshare's servers and Tymnet data network into a major player in the Information Services market. Microdata's systems were integrated into many parts of McDonnell Douglas, but Tymnet never was. MDC really did not seem to understand the telecommunications market. After five years, peace was breaking out in many places in the world and McDonnell Douglas sold off MDNSC and MDFSC at a profit for much needed cash.
Earlier, in 1986, the Canadian Radio-television and Telecommunications Commission liberalized the interconnection rules in the provinces it then regulated and this allowed McDonnell Douglas to expand the network into select Canadian cities. The Canadian operation was part of McDonnell Douglas Computer Systems Company as this was the only MDxxx company operating in Canada. MDCSC hired David Kingsland to spearhead this expansion into Canada.

Sold to British Telecom

BT Tymnet, BT North America, BTNA

On July 30, 1989, at the Marriott Hotel in Santa Clara, it was announced that British Telecom was purchasing McDonnell Douglas Network Systems Company, and McDonnell Douglas Field Service Company was being spun off as a start-up called NovaDyne. British Telecom wanted to expand and the acquisition of Tymnet, which already a worldwide data network, was projected to help to achieve that goal. On November 17, 1989, MDNSC officially became BT Tymnet with its parochial U.S. headquarters in San Jose, California. BT brought with it the idea of continuous development with teams in America, Europe, and Asia-pacific all working together on the same projects. BT renamed the Tymnet services, Global Network Services.
British Telecom brought new life to the company with development of hardware and software for the Tymnet data network using contacts BT already had with telecommunication hardware vendors. There was a trial of "next-generation" nodes scattered throughout the network, called "TURBO engine nodes" based on the Motorola 68000 family. In the mid to late 1980s, serious node-code development was migrated from the PDP-10s to UNIX. Sun-3 and later Sun-4 workstations and servers were purchased from Sun Microsystems, though the majority of PDP-10s were still around in the early '90s for legacy code, as well as documentation storage. Eventually, all of the code development trees were on the Sun-4s, and the development tools had been ported to SunOS.
Another project begun a few months before the BT purchase was to migrate the Tymnet code repository from the PDP-10s to Sun systems. The new servers were dubbed the Code Generation Systems or CGS. They were initially six Sun-3 servers upgraded eventually to two Sun-4/690 servers for redundancy. A second pair of servers for catastrophic failover were also installed in Malvern, PA and later moved to Norristown, PA as part of later site consolidation efforts. After the migration, there was code for more than 6000 nodes and 38,000 customer interfaces.
Tymnet was still growing, and at several times reached its peak capacity when some of its customers held network intensive events. One of these of note was a live, on-line presentation and chat on America On-Line with Michael Jackson. Tymnet usage statistics showed AOL's call capacity was greater than its maximum volume for the duration of the event.