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Telenet was a packet switched network which went into service in 1974. It was the first publicly available commercial packet-switched network service.

The original founding company, Telenet Inc., was established by Larry Roberts (former head of the ARPANet), 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.


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 switching fabric, a shared bus in modern terms, among the microprocessors .

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.

Accessing the Network

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.

Computer Access

Computers supporting the X.25 protocol could connect directly to switching centers. These connections ranged from 2.4 to 56 kbit/s.

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.

PC Pursuit

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 a forerunner of Voice over IP services.

Cities accessible by PC Pursuit

City Code Area Code City
AZPHO 602 Phoenix, Arizonamarker
CAGLE 818 Glendale, Californiamarker
CALAN 213 Los Angeles, Californiamarker
CODEN 303marker Denver, Coloradomarker
CTHAR 203 Hartford, Connecticutmarker
FLMIA 305 Miami, Floridamarker
GAATL 404marker Atlanta, Georgiamarker
ILCHI 312, 815 Chicago, Illinoismarker
MABOS 617 Boston, Massachusettsmarker
MIDET 313 Detroit, Michiganmarker
MNMIN 612 Minneapolis, Minnesotamarker
NCRTP 919 Research Triangle Park, North Carolinamarker
NJNEW 201 Newark, New Jerseymarker
NYNYO 212marker, 718marker New York Citymarker
OHCLV 216 Cleveland, Ohiomarker
ORPOR 503marker Portland, Oregonmarker
PAPHI 215marker Philadelphia, Pennsylvaniamarker
TXDAL 214, 817 Dallas, Texasmarker
TXHOU 713 Houston, Texasmarker
WIMIL 414 Milwaukee, Wisconsinmarker

See also


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