networking was about connecting terminals to their hosts. In the IBM-dominated world of MIT44 Lincoln Moffett RCC49 CORDACOM RCC71 AMES16 BBN40 AMES15 BBN63 SRI51 Xerox BBN72 Stanford Harvard Tymshare DTI WPAFB Sumex DARCOM Aberdeen ANDRW Hawaii ACCAT NOSC Scott NORSAR ISI27 MITRE Pentagon ISI52 ISI22 Gunter Bragg Collins Eglin Robins London Texas Satellite circuit Pluribus IMP Pluribus TIP Figure 4.1 ARPAnet map from 1980 [3]. The Great Telecom Meltdown mainframes, the terminals were typically intelligent devices, block-mode termi- nals like the 3270 family, that performed local screen editing under tight control of the host. In the alternative computer universe then dominated by minicom- puter vendors such as DEC and Hewlett-Packard Inc. (HP), terminals were typically "dumb" character-by-character asynchronous devices. AT&T's own Teletype Corp. had been a large supplier of terminals to minicomputer users in the 1960s and early 1970s, but its slow teleprinters (designed primarily for use as Telex machines) were being replaced by backward-compatible cathode-ray- tube terminals. In either case, the minicomputer terminal was more likely to be hard-wired to a small local machine. Big mainframes, on the other hand, were more likely to be located in a "glass house" computer center some distance away, SO terminal-to-host data communications, or "teleprocessing" technology, was important. Minicomputer users were more concerned with host-to-host interconnection. One very important network technology was the packet-switching proto- col suite based on CCITT Recommendation X.25. This was developed in the mid-1970s as a way to reconcile competing packet-switched networks developed in several countries. (Like many CCITT Recommendations, as their standards were formally known, there was substantial wiggle room; each X.25 network had its own "profile" and actual devices attached to it required significant cus- tomization.) The design center was connecting asynchronous terminals to remote hosts, as an alternative to using modems