Telenet was an American commercial packet switched network which went into service in 1974. It was the first packet-switched network service that was available to the general public. Various commercial and government interests paid monthly fees for dedicated lines connecting their computers and local networks to this backbone network. Free public dialup access to Telenet, for those who wished to access these systems, was provided in hundreds of cities throughout the United States.
- Internal Network Technology
- Basic Asynchronous Access
- Other Access Protocols
- PC Pursuit
The original founding company, Telenet Inc., was established by Bolt Beranek and Newman (BBN) and recruited Larry Roberts (former head of the ARPANet) as President of the company, and Barry Wessler. GTE acquired Telenet in 1979. It was later acquired by Sprint and called "Sprintnet". Sprint migrated customers from Telenet to the modern-day Sprintlink IP network, one of many networks composing today's Internet. Telenet had its first offices in downtown Washington DC, then moved to McLean, Virginia. It was acquired by GTE while in McLean, and then moved offices in Reston, Virginia.
Under the various names, the company operated a public network, and also sold its packet switching equipment to other carriers and to large enterprise networks.
After establishing "value added carriers" was legalized in the U.S., Bolt Beranek and Newman (BBN) who were the private contractors for ARPANET set out to create a private sector version. In January 1975, Telenet Communications Corporation announced that they had acquired the necessary venture capital after a two-year quest, and on August 16 of the same year they began operating the first public packet-switching network.
Originally, the public network had switching nodes in seven US cities:
The switching nodes were fed by Telenet Access Controller (TAC) terminal concentrators both colocated and remote from the switches. By 1980, there were over 1000 switches in the public network. At that time, the next largest network using Telenet switches was that of Southern Bell, which had approximately 250 switches.
Internal Network Technology
The initial network used statically-defined hop-by-hop routing, using Prime commercial minicomputers as switches, but then migrated to a purpose-built multiprocessing switch based on 6502 microprocessors. Among the innovations of this second-generation switch was a patented arbitrated bus interface that created a switched fabric among the microprocessors. By contrast, a typical microprocessor-based system of the time used a bus; switched fabrics did not become common until about twenty years later, with the advent of PCI Express and HyperTransport.
Most interswitch lines ran at 56 kbit/s, with a few, such as New York-Washington, at T1 (i.e., 1.544 Mbit/s). The main internal protocol was a proprietary variant on X.75; Telenet also ran standard X.75 gateways to other packet switching networks.
Originally, the switching tables could not be altered separately from the main executable code, and topology updates had to be made by deliberately crashing the switch code and forcing a reboot from the network management center. Improvements in the software allowed new tables to be loaded, but the network never used dynamic routing protocols. Multiple static routes, on a switch-by-switch basis, could be defined for fault tolerance. Network management functions continued to run on Prime minicomputers.
Its X.25 host interface was the first in the industry and Telenet helped standardize X.25 in the CCITT.
Basic Asynchronous Access
Users could use modems on the Public Switched Telephone Network to dial TAC ports, calling either from "dumb" terminals or from computers emulating such terminals. Organizations with a large number of local terminals could install a TAC on their own site, which used a dedicated line, at up to 56 kbit/s, to connect to a switch at the nearest Telenet location. Dialup modems supported had a maximum speed of 1200 bit/s, and later 4800 bit/s.
For example, a customer in NYC could dial into the local number, then type in a command similar to:
which would connect (that "c") them to a computer system designated as number "555" located in the same vicinity as the standard telephone "area code" 301.
One significant customer was an early (what would now be called) internet service provider The Source which had their equipment in Mclean, Va. Telenet offered a much lower nighttime rate when there were few corporate customers, and this let The Source set up a modestly priced offering to tens of thousands of customers. Another prominent customer in the 1980s was Quantum Link (now AOL).
Other Access Protocols
Telenet supported remote concentrators for IBM 3270 family intelligent terminals, which communicated, via X.25 to Telenet-written software that ran in IBM 370x series front-end processors. Telenet also supported Block Mode Terminal Interfaces (BMTI) for IBM Remote Job Entry terminals supporting the 2780/3780 and HASP Bisync protocols.
In the late 1980s, Telenet offered a service called PC Pursuit. For a flat monthly fee, customers could dial into the Telenet network in one city, then dial out on the modems in another city to access bulletin board systems and other services. PC Pursuit was popular among computer hobbyists because it sidestepped long-distance charges. In this sense, PC Pursuit was similar to the Internet.