Between 1969 and 1975 the ARPANET expanded at the rate of about 10 IMP per years (to approximately 60 IMPs total). Over the period from July 1 to December 31, 1975, the ARPANET operation was phased over from ARPA to the Defence Communications Agenca (DCA) to be run as an operational network, although it continued to be involved in communications R&D experiments. By 1982, there were about 90 IMPs in the ARPANET and the government made the decision that the ARPANET would be the foundation of the Defense Data Network (DDN). Creation of DDN involved splitting the existing ARPANET into two parts—a part which was still known as ARPANET and served non-military users, and a part which was known as MILNET and served military users. (The two parts could communicate in a controlled way by devices called mail bridges.) Also over this period, the ARPANET (in its pre-DDN and DDN form) became a part of many early Internet experiments and thus the backbone of the Internet in its early growth period. In 1988 steps began to dismantle the ARPANET [McKenzie94]. From relatively early in its ARPANET effort, BBN also had aspirations for expanding upon and exploiting the ARPANET technology beyond the ARPANET, both elsewhere in the government and commercially. Relatively early on a slightly modified version of the 516 IMP technology was deployed in the U.S. intelligence community [COINS].
In 1972 BBN organized a commercial packet-based telecommunications carrier known as Telenet which originally used a version of the 516 IMP code running on Honeywell 716 computers but later built their own computer and redid the software. BBN made consulting agreements with Logica in the U.K. and SESA in France for them to bid the 516/316 IMP technology, and BBN bid on other commercial networks (based on ARPANET technology) itself, for instance at Citibank and On-line Systems. By 1974 BBN had developed the Pluribus parallel processor for which it developed software interoperable with the 516/316 IMP system. In time BBN started its own computer company (BBN Computer Corporation) which original handled the hardware maintenance contracts for BBN-delivered networks (as well as trying to be a mini-computer vendor more generally). By 1982, the name of BBNCC was changed to BBN Communications Corporation and its activities were refocused on networking.
From this part of the company, BBN delivered many commercial, military and other networks around the world.1 BBNCC supported the 516/316 IMP technology, the Pluribus IMP technology, and developed new IMP technology based on BBN’s C/30 and C/300 computers. An overview of these various systems is shown in Figure 1. BBN’s ARPANET technology also influenced the design of several non-BBN networks. The LFK Network was a deliberate copy of the ARPANET code running on Norsk Data computers and rewriting the IMP code from scratch [Liaaen02]. The founders of Packet Communications Corporation (who left BBN a little before Telenet was founded) had a copy of the IMP system listing (BBN was required to give copies to companies which asked for a slightly handling charge), but perhaps did not closely follow BBN’s IMP system design. Other places, for example, at least one company in Japan, studied the function of the original ARPANET IMP, and it influenced the design of their network.
More generally, many of the technology approaches originally demonstrated in the ARPANET have become part of the DNA of modern data communications (e.g., the Internet): dynamic routing, operation without central control, packet flow control and reliable transmission, its operating philosophy, its engineering approach to standards, etc.).