The Original NSFNET Backbone

The Original NSFNET Backbone

NSFNET backbone has the most interesting history and used the most interesting technology. The backbone evolved in four major steps; it increased in size and capacity at the time the ARPANET declined until it became the dominant backbone in the Internet. The first version was built quickly, as a temporary measure. One early justification for the backbone was to provide scientists with access to NSF supercomputers. As a result, the first backbone consisted of six Digital Equipment Corporation LSI-ll microcomputers located at the existing NSF supercomputer centers.

At each site, the LSI-11 microcomputer ran software affectionately known as fuzzball? code. Developed by Dave Mills, each fuzzball accessed computers at the local supercomputer center using a conventional Ethernet interface; it accessed leased lines leading to fuzzballs at other supercomputer centers using conventional link-level protocols over leased serial lines. Fuzzballs contained tables with addresses of possible destinations and used those tables to direct each incoming packet toward its destination.

The primary connection between the original NSFNET backbone and the rest of the Internet was located at Carnegie Mellon, which had both an NSFNET backbone node and an ARPANET PSN. When a user, connected to NSFNET, sent traffic to a site on the ARPANET, the packets would travel across the NSFNET to CMU where the fuzzball would route them onto the ARPANET via a local Ethernet. Similarly, the fuzzball understood that packets destined for NSFNET sites should be accepted from the Ethernet and sent across the NSF backbone to the appropriate site.