Internet 101

The Internet as it stands today is a marvel to look at. You are able, at the click of a mouse, to load a web page from Australia and display it in front of you in the United Kingdom with seamless ease. Moving large files around the world is a snap. Video conferencing over the Internet actually works now. All of these functions rely on the resilience of the Internet and the technology that has driven it to help the Internet become an important part of our society.

In the early 1960s, during the Cold War, the U.S. government was concerned with military threats affecting homeland security that could cause the breakdown of communications between one part of the United States and another. Such a lack of communication would prove disastrous to say the least. What was needed was a communications network that was resilient to those types of disasters, and the U.S. government decided to commission the Defense Advanced Research Projects Agency (DARPA) to design this resilient, scalable technology. DARPA's goal was to use technology in defense and give the United States a competitive advantage in times of war.

This was no small feat in those days, and some of the best minds in the world worked on this problem for many years. These minds managed to design not only the physical layout of this resilient system, but also the protocol used to move data from one machine to the next. The protocol eventually became known as the Transmission Control Protocol/Internet Protocol (TCP/IP).

The original Internet was known as the Advanced Research Projects Agency Network (ARPANET) and consisted of fewer than ten main routing points across the United States in universities and government sites. These routing points were the backbone of the communications network that grew steadily over time to connect many educational establishments to one another. This pushed the growth of the technology that drove the Internet, both physically and logically. Applications were designed to work with the new TCP/IP protocol, from simple file transfer (FTP — File Transfer Protocol) to mail (SMTP — Simple Mail Transport Protocol).

The sharing of information drove the expansion of the Internet to exponential proportions with Request for Comment documents (RFCs). RFCs solicited feedback on proposed standards and then, once comments were integrated, formed the basis of standards for Internet technologies. These are still used to this day to put feelers out to peers over new enhancements to protocols and new technology that helps make the Internet what it is today.

If you are interested in reading the RFCs that formed the basis of the Internet as we know it today (and many newer ones), search and

The Internet is a place for pioneers to shape society in one form or another; it has provided users with something that has truly revolutionized the way we communicate and work.

In the preceding section, we discussed how TCP/IP was designed as a resilient network protocol and about how moving data from one part of the world to another is seamless. This is no easy task, and TCP/IP is able to do this for two fundamental reasons — it is simple in its design, and it is open.

A protocol is classified as open when every single person in the world is able to see how it works, right down to the wire.

TCP/IP is based on a layered architecture, as are many network protocols. These layers form the basis of network abstraction. By abstracting layers from each other, you can make sure the technology can grow to meet the demands placed upon it.

Imagine that the TCP/IP protocol was designed and implemented over 20 years ago. With most things in computing, a lot changes in 10, let alone 20 years, but TCP/IP has managed to keep up with trends in computing and networking. As network speeds have gotten faster, the protocol's abstract nature has prevented it from being tied to a technology that is 20 years old.

Every abstracted network protocol adheres to, either loosely or strictly, the International Organization for Standardization's (ISO) standard seven-layer Open Systems Interconnect (OSI) model (see Figure 6-1). It provides a general layered architecture that defines a way to design a network protocol.

From the bottom up, you find the following layers:

■ Physical layer: Deals with how information is transmitted over a medium, whether it is copper or fiber Ethernet, wireless networking, or satellite transmission. This layer has no concept of the upper layers and does not need to, as it is concerned only about getting information safely from one place to another over a medium.

■ Data link layer: Concerned with the encapsulation of data from the upper layers in preparation for moving to the wire. Protocols in this layer can be Ethernet or token ring.

■ Network layer: The network layer is used to define addressing schemes for nodes and networks. It is not concerned with the accuracy of the data it is encapsulating or what format the data is in. Its only concern is that the data is able to get from point A to point B.

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