Techopedia explains
Internet Backbone
Some of the largest companies running different parts of the Internet backbone include UUNET, AT&T, GTE Corp. and Sprint Nextel Corp. Their routers are connected with high-speed links and support different range options like T1, T3, OC1, OC3 or OC48.
A few key features of an Internet backbones include:
- ISPs are either connected directly to their contingency backbones or to some larger ISP that is connected to its backbone.
- The smaller networks are interlinked to support the multiversatile backup that is required to keep the Internet services intact in case of failure. This is done through transit agreements and peering processes.
- The transit agreement is a monetary contract between several larger and smaller ISPs. It is initiated to share traffic loads or to handle data traffic in case of a partial failure of some networks. In peering, several ISPs also share features and traffic burden.
The first Internet backbone was named NSFNET. It was funded by the U.S. government and introduced by the National Science Foundation (NSF) in 1987. It was a T1 line that consisted of approximately 170 smaller networks operated at 1.544 Mbps. The backbone was a combination of fiber-optic trunk lines, each of which had several fiber-optic cables wired together to increase capacity.