The ARPANET architecture called for specialized network communication computers called Interface Message Processors (IMPs). Each IMP was to connect from 1-4 hosts, and be linked to from 3-5 other IMPs. The original message format specification had only a 6-bit address, limiting the network to 64 IMPs. IMPs performed such communication tasks as routing, error checking, flow control, and network management. The hosts were heterogeneous, time-sharing systems, isolated from their IMPs by well-defined electrical and software interfaces. TIPs, terminal IMPs, were later designed to connect terminals to the net without the need for an intermediate host. (A TIP was a mini-host plus an IMP).
The first IMP was booted up at UCLA in 1969, and was quickly linked to three others at UC Santa Barbara, University of Utah, and the SRI. The net grew like a weed. International links to Norway and England were set up in 1973. (Norway was chosen for military purposes-a NATO nation near the Soviet Union). When the ARPANET was turned over to the Defense Communication Agency for production work (and cloning) in 1975, there were 57 nodes (see Table 2).
The ARPANET was widely publicized in articles, a short documentary, and a major public demonstration in 1972, and the word got out. As with time-sharing understood its value. (My eyes were opened during a joint-authoring exercise in which I collaborated with people around the nation using a Teletype with an acoustical coupler in my den at home.) It was clear to academic researchers their counterparts at centers with ARPANET connectivity had an advantage.




NSF

In 1974 the NSF Computer Science and Engineering Advisory Panel recommended "the NSF provide to qualified computing researchers easy access to an international computer network. This access would create a frontier environment that would offer enhanced communication, collaboration, and the sharing of resources among geographically separated or isolated researchers." [6]
NSF funded THEORYNET, a central email computer at the University of Wisconsin, where roughly 100 theoretical computer scientists dialed in using modems or X.25 and exchanged email. There were scattered UUCP efforts, but relatively few computer scientists were networked. THEORYNET organizer Larry Landweber convened an NSF sponsored meeting in 1979 to plan connectivity for all compute! scientists. The result, after two major review and revision cycles, was the establishment of CSNET in 1981 [6]. CSNET was seeded with a $5 million grant from NSF, which also managed the project for two years, before turning it over to BBN. It provided email service for small institutions, TCP/IP connectivity over X.25 or the ARPANET for larger institutions, and name server. The mail software was provided by the University of Delaware, and TCP/IP, which had become a Department of Defense standard came from ARPA.
CSNET was arguably the first ISP. Their charter called for financial independence after five years, and member institutions paid either $30,000 (industrial), $10,000 (government or nonprofit) or $5,000 (university) per year. This was later reduced for small computer science departments. CSNET was self-sufficient under BBN, and, by 1985, had over 165 member institutions' (mostly academic) in the U.S. and abroad. CSNET, along with Bitnet, was eventually transferred to the Corporation for Research and Education Networking.
By the mid-1980s, the value of networks was abundantly clear, and many discipline-specific, state and regional, corporate, and campus networks were operating [15, 23]. It was time to link these efforts, and move networking from computer science to the entire university and research community, then to the commercial sector. Again, NSF provided seed funding and leadership in creating NSFNET [8].

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