Tymnet
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Tymnet was an international computer network based on the X.25 protocol.
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Tymshare time-sharing
Tymshare was founded in 1966 as a computer services company, that is, it sold computer time (time-sharing), and provided software packages for users. It had two SDS/XDS 940 computers; access was via direct dial-up to the computers.
Tymnet network
This United States-wide commercial computer network was used for remote-login and file-transfer.
Beginnings
In 1968, Ann & Norm Hardy, Bill Frantz, Joe Rinde (writer of the original supervisor program) and LaRoy Tymes developed the idea of using remote sites with minicomputers to communicate with the mainframes. This was the beginning of the Tymnet network. During those first years, Tymshare and its direct customers were its only users. When Tymshare started using Interdata 7/32 minicomputers as nodes, they started developing Tymnet on PDP-10. Tymshare sold the Tymnet network software to TRW, who created their own private network (which was not called Tymnet).
Organization and functionality
In its original implementation, the network supervisor contained most of the intelligence in the network. The supervisor performed login validations as well as circuit management. Circuits were character oriented and the network was oriented towards interactive character-by-character full duplex communications circuits. The supervisor ran on an XDS 940 host, and the nodes were limited-capacity Varian minicomputers. With the development of the Tymnet Engine, the power of the nodes in the network increased considerably, and the supervisor became a node in the network, running in an Engine. The major part of the intelligence of the network still resided in the supervisor. 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 sets up its own "permuter tables", eliminating the need for the supervisor to keep copies of them, and has greater flexibility in handling its inter-node links. There was a clever scheme to switch the echoing function between the local node and the host based on whether or not a special character had been typed by the user. Data transfers were also possible via "auxiliary circuits".
Comparison with ARPANET
Another example of a big computer network is ARPANET which uses standard packet switching, with dynamic rerouting of messages, while Tymnet uses multiplexed packet switching and centrally directed, fixed message paths. Each node in ARPANET has a global picture of the network as it exists at any given moment. The node then decides which direction it should send a packet at that time. This requires large amounts of buffer space for nodes and hosts in the network because a large message consisting of several packets could arrive with the packets out of sequence, due to their having taken different routes to their destination. In Tymnet, once the destination is established, either by default or by the users' specifications, the signal path is established as part of the log-in sequence. This virtual circuit will go over this path, as a part of various multiplexed packets. The disadvantage of this method is that if a line goes out, all of the users on that line will be knocked off the network, and have to log back in again.
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 Inc. 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.
Before 1996 TTS/PAPER (the Trouble Ticket System) 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 for Tymshare. The application was written in FORTRAN and used the 1022 database. After 1996 the DEC PDP-10s 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 Microsystems 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.
In 1984 Tymnet was bought by the McDonnell Douglas Corporation. In the very late 80's / early 90's, 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 80's, serious node-code development was migrated off of the PDP-10's to Sun4 machines, though the majority of PDP-10's were still around in the early 90's for some legacy code, as well as documentation storage. By this time, all of the code development trees were on the Sun4's, and the development tools (NAD, etc.) had been ported to SunOS. In 1989, BT North America bought Tymnet from the McDonnell Douglas Corporation. In 1993 MCI Communications(MCI) bought Tymnet (stock exchange) in order to create Concert. The new name is CPS (Concert Packet-switching Services). Tymnet has outlived its parent company Tymshare. In May 1994, there were still three DEC KL-10s under TYMCOM-X. At this time, we have approximately 5000 nodes in the network, in 30 foreign countries. Over a packet-switching-network a various number of protocols can be run. The most used protocols are X.25, asynchronous (ATI/AHI) and SNA.
Although BT is fully out of the picture now(?), and MCI was acquired by WorldCom, Tymnet has so far survived its transient past to remain a strategically valuable network. It now has about 5200 nodes, 4000 of which are in the U.S. However, as the network turned 30 years old, a major upgrade was necessary if Tymnet was going to continue as a cost-effective backbone.
Dennis Jonas (advisory engineer for local and strategic engineering) planned the networkwide upgrade, which began in 1996 and is still ongoing. The project aimed to reduce operating costs for Tymnet's 115 legacy X.25 switching centers, while migrating away from a technical and cumbersome assembly language operating system that Tymnet had developed. The company wanted to replace proprietary equipment and protocol with open, modern off-the-shelf solutions that could improve the efficiency of these centers. MCI was seeking to install about one new system for every five to 10 pieces of legacy server equipment housed in its switching centers. MCI also wanted to reduce the number of access nodes in the network by closing more than 400 asynchronous access sites and back-hauling the access points to other nodes. The eventual goal is to collapse more than 500 access nodes into about 50.
Jonas decided that the Solaris operating system developed by Sun Microsystems fit the bill for Tymnet's operations and management needs. Although rack-mount solutions tend to cost more than other options, the ease and speed of installing rack-mount systems promised to minimize the time and hassle inherent to a broad network upgrade. MCI contracted with Sun reseller Artecon to carry out the upgrade. Artecon's rack-mount PowerSphinx solution, based on Sun's Sparc 20, supports a -48 volt DC power environment for standard 110-volt servers and peripherals, and it is compliant with Bellcore NEBS. MCI installed 25 Sphinx units in switching centers in Dallas and Chicago during the second half of 1996 and so far has installed about 120 units in these and other cities, including Los Angeles, San Jose, Doraville, Ga., and Fairfax, Va.
Upgrades that previously took days are now taking only a few minutes because rack-resident equipment can be easily moved in and out of rack-mount designs. In Artecon's solution, the racks offer unobstructed backplane access, while the workstations stay in their original casing. These facts also bode well for the future because MCI will be able to conduct quick, smooth upgrades whenever Sun offers new Sparc versions. Minimizing labor time is not the Sphinx rack's only benefit. The rack is designed only slightly larger than the Sparc 20 itself, so that the server footprint is kept to a minimum.
That is especially true of the last few years. Many telcos hoping to establish more efficient operations have launched projects to re-engineer their COs only to find that the execution of these projects is impractically slow or complex. However, competition is a forceful hand if ever the industry has seen one, and modernizing the network every 30 years will no longer suffice. Rack-mount frameworks may be a quick, methodical solution for bringing networks into the 1990s and beyond.
Because of the BT / MCI splitup, it was not 100% sure what would happen in the future. The most logical step was that the US part of Tymnet would remain within MCI. The non-US part would likely remain Concert. MCI migrated their nodes to SUN Sparcs 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 packetswitching network will be migrated to an IP based platform by the end of 2002. In 2004, Tymnet was officially ceased.