How the Internet Looks
You'll have to look hard to find a description of what the Internet really is. Most descriptions of the Internet, unfortunately, favor simplicity over detail, and the reader is left with little more than the vague impression that the Internet is "a highway for data."
In fact, the details of Internet topology are so complex that few professional network administrators can tell you precisely what happens to the data that leaves their lines. Nor is it necessary for them to know. The stability and versatility of TCP/IP make it possible for a datagram to enter the cloud of the Internet and emerge without oversight in exactly the right place on the other side of the Earth. Where does the datagram go when it enters that cloud?
Today's Internet is too big for the structure depicted in Figure 10.5, in which a single backbone serves an orderly constellation of autonomous networks. Today's Internet consists of multiple backbone networks, many of them managed by private corporations such as Sprint or WorldCom.
By the Way
It should come as no surprise that long distance phone companies such as Sprint and WorldCom are major players in the Internet topology. The presence of these long distance carriers underscores the fact that the Internet, like the phone system, is built from lots and lots and lots of cable strung over vast distances.
These backbone networks intersect at large switching facilities called Network Access Points (NAPs). WorldCom's MAE East (in the Washington, D.C., area) and MAE West (in the San Jose, California, area) are two of the busiest and most important NAPs in the United States. The MAE East and MAE West sites are considered national connection points for major ISPs. A collection of regional NAP sites are in locations such as Chicago, Dallas, Houston, and New York.
ISPs attach to the Internet through a NAP. NAP sites such as WorldCom's MAE sites do not provide routing services. Instead, the individual ISPs supply and maintain their own routers within a secure space made available at the NAP facility.
The ISP leases what is called a Point of Presence (POP) connection (see Figure 16.1). ISPs that connect to big NAP sites are usually major Internet vendors. Some of these ISPs might be wholesalers who lease bandwidth to smaller ISPs. The smaller ISPs might lease the lines to even smaller ISPs or to corporations.
The Internet, therefore, consists of thousands of intertwined business arrangements—covering lines, connections at the end of lines, bandwidth leases, and hundreds of ISPs providing services for users, businesses, and organizations. You can see why the Internet is often depicted as a cloud: From a distance it looks like a single object, but as you move closer, you can never really find the center, because it is everywhere around you, however you look at it.
The fact that the Internet is a single cohesive entity is not because of its physical connectivity, but because
In Hour 1, "What Is TCP/IP?", you learned about the organizations governing the Internet, including the Internet Advisory Board (IAB) and the Internet Engineering Task Force (IETF). The language of the Internet is, of course, TCP/IP, but it is worth highlighting a significant element of the TCP/IP infrastructure that provides for Internet messaging on a global scale: the common naming and numbering system overseen by ICANN. The DNS naming system is more than the name resolution protocols described in Hour 11, "Name Resolution." Name service on a global scale requires an enormous human effort to manage the lower-tier organizations that manage the orderly assignment of Internet names. Without the powerful DNS naming system, the Internet would not be the pervasive force in daily life it is today.