Information about Tymnet

Tymnet was an international data communications network headquartered in San Jose, California that utilized virtual call packet switched technology and used X.25, SNA/SDLC, ASCII and BSC interfaces to connect host computers (servers) at thousands of large companies, educational institutions, and government agencies. Users typically connected via dial-up connections or dedicated async connections. The business consisted of a large public network that supported dial-up users and a private network business that allowed government agencies and large companies (mostly banks and airlines) 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 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 was officially 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 as well.

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. For various technical reasons, the connection was not entirely "invisible", and sometimes required the user to enter arcane commands to make 8-bit clean connections work properly for file transfer.

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 point in 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

Tymshare was founded in 1966 as a time sharing company, selling computer time and software packages for users.[1] 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.[2]

In 1968, Ann & Norm Hardy, Bill Frantz, Joe Rinde, 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 called a "Supervisor" 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. The Varian 620i was also used for the TYMNET nodes. During those first years, Tymshare and its direct customers were the network's only users.

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 Interdata, they started developing Tymnet on 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.

Tymnet Inc spun off

In about 1979, Tymnet Inc. was spun off from Tymshare Inc. to continue administration and development of the network. 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.

Trouble reporting on Tymnet was done through TTS/PAPER (the Trouble Ticket System), which ran on two mainframes from Digital Equipment Corporation. These PDP-10 computers, model KL-1090, were accessible via the Tymnet Packet Network as Tymshare hosts 23 and 26. Each computer was the size of 5 refrigerators, and had a string of disks that looked like 18 washing machines. Their power supplies produced +5 volts at 200 amps (non-switching) making them expensive to operate. The PDP-10s ran TYMCOM-X, an offshoot of TOPS-10 modified by Tymshare. The application was written in FORTRAN and used the 1022 database.

Concert

In 1984 Tymnet was bought by the McDonnell Douglas Corporation. In the very late '80s / early '90s, there was a trial of "next-generation" nodes scattered throughout the network, called "TURBO nodes" and based on the Motorola 68000 family. Also, in the mid to late '80s, serious node-code development was migrated off of the PDP-10s to Sun Microsystems Sun-3 (and later Sun-4) machines, though the majority of PDP-10s were still around in the early '90s for legacy code, as well as documentation storage. By this time, all of the code development trees were on the Sun-4s, and the development tools (NAD, etc.) had been ported to SunOS.

In 1989, BT North America bought Tymnet from McDonnell Douglas, and renamed the network BT Tymnet.

In 1993 MCI Communications (MCI) bought Tymnet in order to create Concert. The new name was CPS (Concert Packet-switching Services). Tymnet had outlived its parent company Tymshare.

In May 1994, there were still three DEC KL-10s under TYMCOM-X. At this time, the network had approximately 5000 nodes in 30 foreign countries. A variety of protocols can be run over a single packet-switching-network, and Tymnet's most-used protocols were X.25, asynchronous (ATI/AHI) and SNA.

Major upgrades

In 1996 the DEC PDP-10s that ran Tymnet's trouble-ticket system were replaced by PDP-10 clones from XKL PLC. They were accessible via TCP/IP as ticket.tymnet.com and token.tymnet.com, by both TELNET and HTTP. A low-end workstation from Sun was used as a telnet gateway; it accepted X.25 logins from the Tymnet network and forwarded them to "ticket" and/or "token". The XKL systems ran TOPS-20. The application was ported to a newer version of the Fortran compiler, and still used the 1022 database. After 1998, both systems were decommissioned.

Migration from X.25 to IP

Because of the BT / MCI split up, it was not 100% sure what would happen in the future. The most logical step was that the U.S. part of Tymnet would remain within MCI. The non-US part would likely remain Concert. MCI migrated their nodes to Sun SPARC systems and Concert migrated their nodes to Telematics ACP/PCPs running TYM2. It is known that Tymnet is providing a lot of financial profit to their owners because of the worldwide service availability and reliability.

The Concert packet switching network was migrated to an IP based platform by the end of 2002. In February 2004, Tymnet was officially shut down.[3]

See also

• DATAPAC
• ConnNet

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X.25 is an ITU-T standard protocol suite for connection to packet switched wide area networks using leased lines, the phone or ISDN system as the networking hardware. It was developed before the OSI Reference Model or the equivalent Network Access Layer of the DoD protocol model,
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Systems Network Architecture (SNA) is IBM's proprietary networking architecture created in 1974. It is a complete protocol stack for interconnecting computers and their resources. SNA describes the protocol and is, in itself, not actually a program.
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Synchronous Data Link Control (SDLC) is a computer communications protocol. It is the layer 2 protocol for IBM's Systems Network Architecture (SNA). SDLC supports multipoint links as well as error correction.
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American Standard Code for Information Interchange (ASCII), generally pronounced ask-ee IPA: /ˈæski/ ( [1] ), is a character encoding based on the English alphabet.
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Binary Synchronous Communication (BSC or Bisync) is an IBM link protocol, announced in 1967 after the introduction of System/360. It replaced the synchronous-transmit-receive (STR) protocol used with second generation computers.
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In telecommunications, a circuit switching network is one that establishes a dedicated circuit (or channel) between nodes and terminals before the users may communicate. Each circuit that is dedicated cannot be used by other callers until the circuit is released and a new
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Varian Data Machines was a division of Varian Associates which sold minicomputers. It entered the market in 1966^[1], but met stiff competition and was bought by Sperry in 1977.^[2]

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The SDS 940 was Scientific Data Systems' (SDS) first machine designed to support time sharing directly, and was based on the SDS 930's 24-bit CPU built primarily of integrated circuits.
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A duplex communication system is a system composed of two connected parties or devices which can communicate with one another in both directions. (The term duplex is not used when describing communication between more than two parties or devices.
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Time-sharing refers to sharing a computing resource among many users by multitasking.
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Varian Data Machines was a division of Varian Associates which sold minicomputers. It entered the market in 1966^[1], but met stiff competition and was bought by Sperry in 1977.^[2]

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1.

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The Model 7/32 and Model 8/32 were 32-bit minicomputers developed by Interdata, Inc. of Oceanport, New Jersey during the 1970s. They are primarily remembered for being the first 32-bit minicomputers, and the first non-PDP computers to run Unix.
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The PDP-10 was a computer manufactured by Digital Equipment Corporation (DEC) from the late 1960s on; the name stands for "Programmed Data Processor model 10". It was the machine that made time-sharing common; it looms large in hacker folklore because of its adoption in the 1970s
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