The most used network in the world.
Made up of thousands of networks of national and state government
agencies, and non-profit organizations and for-profit companies.
Internet Hierarchical Structure
Tier 1: National Internet Service Providers (ISPs)
- Provide services to their customers and sell access to tier 2 and 3 ISPs
- Provide access to their peers (other national ISPs)
Tier 2: Regional ISPs
- Connect to tier 1 ISPs
- Provide services to their customers and sell access to local ISPs
- Provide access to their peers (other regional ISPs)
Tier 3: Local ISPs
- Connected to tier 1 or 2 ISPs
- Sell access to individuals
- Provide access to their peers (other local ISPs)
Network Access Points (NAPs):
Connect tier 1 ISPs together. (Sometimes large tier 2 and 3 ISPs too)
Run by common carriers
Metropolitan Area Exchanges (MAEs):
Connect tier 2 ISPs together. Peering – ISPs at the same level usually do not charge each other for
However higher level ISPs charge lower level ISPs.
E.g. Tier 1 charges Tier 2 and Tier 3
Tier 2 charges Tier 3
Tier 3 charges individuals
Users connect to an ISP through one of the ISPs Point of Presence.
Corporate users have a cost of ISP charges + circuit charges
Backbone for national ISPs uses OC-48 and OC-192, becoming more
Internet Access Technologies
- 56k dial-up lines (mostly rural nowdays)
- Digital Subscriber Line (DSL)
- Cable Modems
Digital Subscriber Line (DSL)
A family of point-to-point technologie