previous | start | next

Modern Internet Structure

The Internet in the USA has always used a backbone topology, with the National Science Foundation Network (NSFNET) providing the original backbone network.
 
In 1995, this structure was privatised, with a variety of commercial organisations (National Service Providers (NSPs)) taking over the backbone functionality. Interconnections between these organisations occur at a number of Network Access Points (NAPs). A NAP can be independently owned. NSPs are said to peer with other NSPs at the NAPs, with (apparently) complex financial and/or cooperative arrangments in place to "carry each other's packets". The worldwide Internet is now structured similarly. We have:
 
NSP, R-ISP and Local ISP Hierarchy
NSPs (or tier-1 providers) provide ISP service to Regional Internet Service Providers (or tier-2 providers) -- ie, R-ISPs are customers of NSPs. R-ISPs can also negotiate private peering agreements, as indicated in the diagram. Retail (also called access, local, or tier-3) ISPs generally are clients of a Regional ISP and offer dial-in (and possibly permanent) services to the public. At each level, we say that a provider has a Point of Presence (POP) at a physical location if customers can connect to it at that location.
 
Note that the distinction between each of these classes of provider can become rather blurred, especially in Australia!
 
Lecture 15: Internet Topology and Structure Copyright © 2004 P.Scott, La Trobe University Bendigo.



previous | start | next