A HIERARCHY OF NETWORKS
Every computer that is connected to the internet is part of a network, even the one in your home. for example, you may use a modem and a dial a local number to connect to an INTERNET SERVICE PROVIDER (ISP). At work, you may be part of a local area network (Lan), but you are most likly still connect to the Internet using ISP that your company has contracted with. When you connect to your ISP, you become part of their network. The ISP may then connect to a larger network and become part of their network.
Most large comunciations comapanies have their own dedicated backbones connecting various regions. In each region, the company has a POINT OF PRESENCE (POP). The POP is a place for local users to access the company's network. The amazing thing here is that there is no overall controlling network. Instead, there are several high-level networks connecting to each other through
Imagine that Comapany B is a corporate ISP. Compant B builds large buildings in major cities and corporations locate their INTERNET server machines in these buildings. Company B is such a large company that it runs its own cables betweeen its buildings so that their are interconnected.
- In this arrangement, all of Company A's customers can talk to each other, and all of Company B's can talk to each other but there is no way they can connect to each other.
In the real INTERNET, dozens of large INTERNET providers interconnect at NAPs in varoius cities and trillons of bytes of data flow between the individual networks at these points. The INTERNET is a collection ofhugh corporate netowrks that aggree to all interconnuncate with each other at teh NAPs. in this way, every computer on the Internet connects to each other.