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.
Lecture 15: Internet Topology and Structure | Copyright © 2004 P.Scott, La Trobe University Bendigo. |