Definition[]
The backbone networks interconnect with each other at a dozen or so sites around the United States (and other similar sites around the world). These points of interconnection are called network access points (NAPs).
Overview[]
The connection is by means of a switching computer which looks at each incoming packet to see where that packet should be routed next. This switching computer is called a "router.”
When several backbones agree to interconnect at a given point, the connection is, loosely speaking, between “peers” rather than hierarchical. Consequently it is common for the owning companies to agree to interconnect without charging each other any fees.