The Digital Research Initiative
The University of North Carolina at Chapel Hill

Part Two: What is the Internet?

The Internet is a global collection of computer networks.

Some people claim that "Internet" is shorthand for "International Network," while others believe "Internet" is short for "Inter-Network." Both ideas are in keeping with the definition of "Internet," as it is an international collection of millions of computer networks.

The individual networks that combine to make the Internet share a common network protocol, TCP/IP (Transmission Control Protocol/Internet Protocol). These networks utilize common methods for identifying member computers and for transmitting information between computers. The best way to understand how these similar computer networks combine to become the Internet is to compare this idea to the United States Postal Service.

The function of the Postal Service is very similar to that of the Internet, as it is designed to transfer information and resources between locations in the United States. Individuals place letters into the Postal Service's care using a common methodology (protocol) and the Postal Service uses a standard method for directing a letter from its source to its destination.

A house with a mailbox is equivalent to a computer on a network. That house's neighborhood with it's Postal Service worker is equivalent to an individual network. With this in mind, consider these two examples:

  1. On Elm Street in Raleigh, North Carolina, the woman who lives in the red house (110 Elm Street) would like to send a complaint letter to the man who owns three barking dogs in the blue house (119 Elm Street). The woman composes a letter to the offensive dog-owner and then delivers it herself to his mailbox. She can easily find the blue house, since it is directly across the street from her.

  2. Down the street, in 200 Elm Street in Raleigh, North Carolina, a woman wishes to send a letter to her grandson, who lives at 318 Oak Street in Springfield, Ohio. She composes the letter, but is unable to deliver it herself, because she does not know how to get to that exact address, or even to Springfield, Ohio. She seeks the help of the Postal Service by properly-addressing the letter and leaving it in her mailbox with the flag up.

    A Postal Service worker takes the letter from the woman's mailbox to the Post Office in Raleigh, NC. While there is no way to send the letter directly to 318 Oak Street in Springfield, Ohio, the staff at the Raleigh Post Office are able to send the letter to the Washington, D.C. Sorting Facility that can route it towards Springfield. The letter is sent to the Sorting Facility, where it is sent to the Springfield, Ohio Post Office, and from there, the letter is given to the Post Office worker assigned to Oak Street. The Postal worker delivers the letter to the mailbox at 318 Oak Street in Springfield, Ohio.

In the first example, we see how a small network operates. Member computers of that network can easily send items to their peers, as they are all within "eyesight" of each other and can easily find one another. In the second example, there is an "inter-network." A member of one network can send items to a member of a second network by passing that item through a system that can "route" the item to its destination. Of particular importance in the second example is how the routing went from a very specific location to a more general location back to a more specific location. Here were the steps:
  • 200 Elm Street in Raleigh, North Carolina (very specific)
  • Raleigh Post Office (less specific)
  • Washington Sorting Facility (general)
  • Springfield Post Office (specific)
  • 318 Oak Street in Springfield, Ohio (very specific)
The critical step is when the staff of the Raleigh Post Office decides that even while it can't transport the letter directly to 318 Oak Street in Springfield, Ohio, they can send the letter to a place where it can be sent in the direction of Springfield, Ohio. This is exactly how the Internet routes traffic.

While houses with mailboxes have street addresses, computers on networks have "IP Addresses" ("IP" refers to "Internet Protocol"). Under the most common standard, these IP Addresses are made up of four numbers between 1 and 255, separated by periods. Here are some example IP Addresses:

  • 64.54.23.198
  • 244.32.121.100
  • 209.178.41.76
While a street address starts specifically and becomes general (house number, then street, thencity, then state/zip), an IP address starts generally and becomes more specific. Typically, the first three numbers represent the network (or "street") and the last number identifies the particular computer (the "house/mailbox"). In the three numbers that represent the network also become more specific, with the first number usually referring to a large block of networks, the second to a smaller block, and the third to an even smaller block.

Let's assume that the computer that has the IP Address of 209.178.41.76 needs to send a piece of data to the computer with the address of 64.54.23.198. The source computer knows from the first three numbers in the target address that the destination computer is in a different network. The source comptuter will need outside assistance to send the data to its destination. Every network on the Internet has at least one member computer that serves as a "gateway" to the outside world. This member is equivalent to the Postal Service workers assigned to Elm Street and Oak Street, as it only has the ability to send data in the correct general direction rather than in the exact direction. This gateway can also receive data from another network and deliver it to a specific member computer in its network. This gateway computer is often a specialized computer, not a normal desktop PC.

The gateway will not know how to send the data directly to the gateway for 64.54.23.198's network, but it will be able to send the data to a larger gateway, called a router, which can make a better decision on the best direction for the data. This is equivalent to Elm Street's Postal Service worker taking the letter to the Raleigh, North Carolina Post Office. The larger router will know of an even larger, more important router that can make the best decision for the direction of the data, and it will send the data to that larger router, just as the Raleigh Post Office will send the letter to the Washington Sorting Facility for routing to Springfield. The larger router sends the data to the router responsible for all networks with "64.54" in their addresses, equivalent to the Springfield Post Office, and the 64.54 router sends the data to the gateway for the "64.54.23" network, equivalent to the Oak Street Postal Worker. This gateway delivers the data to it's target, the computer with the 64.54.23.178 address.

A more clear representation follows:

Postal Service Internet
A letter is sent from 318 Elm Street in Raleigh, NC. Data is sent from 209.178.41.76.
Elm Street's Postal Service worker carries the letter to Raleigh Post Office. The 209.178.41 gateway sends the data to its router.
The Raleigh Post Office sends the letter to thr Washington Sorting Facility. The router sends the data to a larger/important router.
The Washington Sorting Facility sends the letter to the Springfield Post Office. A larger/important router sends the data to 64.54 router.
The Springfield Post Office gives letter to Oak Street's Postal Service worker. The 64.54 router sends the data to the 64.54.23 gateway.
Oak Street's Postal Service worker delivers the letter to 318 Oak Street. The 64.54.23 gateway delivers the data to 64.54.23.198.

While these examples are very simplified representations of both the United States Postal Service and the Internet, they demonstrate how data is sent through the Internet. In the "real world" of the Internet, there are the following differences:

  • There are generally more "stops" along the way at various routers.
  • The data is generally broken up by the source computer into several smaller "packets" that are each treated as individual "letters." The destination computer will reconstruct the data from the packets.
  • Not all networks are represented by the first three numbers of an IP address. Depending on the size of the network, the network can be represented by the first number only, the first two numbers, the first three, or even all four numbers (the last number can represent the network AND the network member). In all cases, the system works like the above example.
The Postal Service analogy can also illustrate the decentralization of the Internet. What would happen if the Washington Sorting Facility were closed due to a hurricane? Would letters not travel from Raleigh to Springfield? Of course not; another Sorting Facility would be available to pick up the Washington Sorting Facility's duties, and the same occurs on the Internet. Many routers can provide direction for data going to a particular address, and if one router is unavailable, the others take up its responsibilities. Generally, routers try to send data along the fastest route, but this is not always possible.

For more information on Internet Routing, please see this page on HowStuffWorks.Com.

Return to Part One | Part Three: What is DNS and How Does It Work?


This site made by
eric
This site was created especially for students of the UNC School of Journalism's
JOMC 050 Class, and anyone else who may be interested.
For more information, please contactdaikat@email.unc.edu