NSFNET
The National Science Foundation Network (NSFNET) was an evolving set of projects that promoted research into advancing networking technology. The name was also applied to the physical network built by NSF contractors to support NSFNET projects.
NSFNET was an important player in the early day of the expansion of the Internet, between 1985 and 1995. The term is used to apply both to a series of projects aimed at improving networking technology, as well as the physical network the National Science Foundation built to link participating researchers to NSF supercomputing sites. Over time, the network was expanded and eventually grew into part of the Internet backbone prior to it's decommissioning in 1995.
NSFNET went online in 1986 with a 56 kilobit per second backbone, and operated as a TCP/IP network. However, that modest backbone proved inadequate just a few months later, and in 1987 and 1988 the network capacity was increased to 1.5 megabits per second. That amount of bandwidth would prove adequate for a few years, but in 1991, the network was upgraded once more to 45 megabits per second using a T3 line.
From its inception, NSFNET was intended to be a research network and not a commercial network. In order to support this purpose, an Acceptable Use Policy was developed and used to determine whether certain uses of the network were acceptable. As traffic on the network increased, and connections to other networks were made, it became increasingly evident that a non-commercial research-only model was not sustainable. In 1995, the physical NSFNET network was transitioned to new commercially-driven and managed infrastructure. While NSFNET projects did continue for a while longer, the NSFNET network and network service were decommissioned at this point.
What was the difference between ARPANET and NSFNET?
ARPANET predated NSFNET by a couple of decades and was decommissioned in large part because of the existence of superior networks like NSFNET. ARPANET, a project of the Department of Defense, was the network where the Internet protocol suite, TCP/IP, was developed and first used. NSFNET followed behind ARPANET and was designed as a network of research centers and supercomputers communicating over a TCP/IP network much as ARPANET before it. With NSFNET online, ARPANET became redundant and was decommissioned in favor of the more advanced network.
Did the National Science Foundation pursue any additional networking initiatives after folding NSFNET?
When NSFNET closed up shop in 1995, the National Science Foundation was already 2 years into developing a more advanced network backbone service called the very high-speed Backbone Network Service (vBNS). The network was developed in conjunction with, and operated by, MCI. The goal of the project was to push information transmission speeds from 155 megabits per second up to 2.5 gigabits per second – a goal that was reached in 1999.
Following the expiration of NSF's contract with MCI, MCI transitioned the use of vBNS to providing commercial networking service to governmental customers. Today, vBNS is part of Verizon who merged with MCI in 2006, and the network is part of Verizon's business-level Internet architecture.