TCP/IP First-Step [Electronic resources] نسخه متنی

The Official Protocol of the Internet

TCP/IP was born approximately 20 years ago. Its precise genesis is hard to pin down because of the way it emerged. Unlike Kazaa or Doom or even Windows 2000, a date when it was first made available to the public just can't be nailed down. For that matter, it isn't possible to identify TCP/IP's creator. It simply wasn't developed by a software development company. Instead, it emerged piecemeal, over time, thanks to the individual efforts and contributions of people who weren't trying to revolutionize the way the world communicated. Their intent was far more humble: They were merely trying to make their own jobs better.

That might sound a little strange. Today, everyone is so spoiled by sophisticated and powerful software that it is difficult imagining what it was like to try and use a computer 20 years ago. Around that same time, 20 years ago, is when TCP/IP and the Internet began their symbiotic lives. Over time, they would jointly revolutionize the way the world communicates. That revolution can be summed up in just one word: interoperability.

There was a time when you could shop around and pick your favorite brand of TCP/IP software. You could then install this software on your computer so that any applications you installed could communicate using TCP/IP. That was back when the Internet hadn't yet become so widely used. The Internet's success forced the manufacturers of operating systems, such as Windows and Linux, to make TCP/IP a built-in part of their operating systems.

Today, interoperability is achieved by interconnecting all the private networks via the same network and then using TCP/IP to communicate. Back in internetworking's early days, the engineers who maintained these different networks for their organizations often created their own software utilitiesthings that made their lives easier or provided some user-requested functionality that was not yet commercially available. Those engineers collectively decided to share their utilities amongst each other. In this manner, different approaches to solving the same problem were aired, and the best ideas prevailed through consensus. If someone didn't like a particular utility or protocol, that was okaythere was no mandate to use it. It was all consensual and voluntary.

Before they knew it, a remarkably sophisticated and feature-rich communications protocol emerged. With each additional contribution, this communications protocol began looking more like today's TCP/IP.

Originally, the collection of communication utilities that emerged from the Department of Defense's (DoD) internetwork was known as the Network Control Protocol (NCP). NCP continued to grow and evolve over time. Today, this collection of protocols and utilities is known as TCP/IP.

Groups of Functions

After learning a little about how TCP/IP emerged, you might be wondering just how schizophrenic and ill behaved a piece of software it is. It's well behaved, but it does look a bit like a Swiss army knifean attachment for everything. Its internal pieces do everything from taking data from applications to preparing it for the network, managing to act like a whole bunch of applications that make networks useful.

The net effect is a powerful suite of communications protocols that work so well and seamlessly, that it's easy to forget that TCP/IP is there at all. It achieves this remarkable feat by playing sort of a zone defense. It organizes related or similar functions into layers and carefully delineates each layer's role and responsibilities. The passing of data between layers also is carefully orchestrated.Chapter 3, "The Quest for Freedom of Choice."

The three main groups of functions can be categorized as follows:

Tools for users

Tools for applications

Tools for the network

Figure 4-1 shows you these categories in a layered reference model. This isn't the real TCP/IP reference model, but it helps keep things in perspective as you walk through more of the details. Besides, these layer names make a lot more sense than the official names!