Oracle8i

Chapter 1: Overview of Networking

A systems administrator I once worked with was fond of saying, "To understand the future, you must examine the past" because our current technology often reflects and encompasses the advances of the past. This book is both an introduction and a guide to interacting with Oracle in a networked environment. However, I believe that to work effectively with the product set, you must know a little about how network components are assembled and, at the very least, understand some of the basic terminology involved. I spent many years hearing others using terms such as "token-ring" and "Ethernet" or "T1 line," without understanding exactly what they were talking about. (I would, of course, never admit that to them!) Therefore, this first chapter is devoted to some of the history of networking, elementary terminology, and network configurations. I'll also describe some of the hardware involved and the protocols used. Although this book is very Oracle networking centered, this chapter will not cover much Oracle-specific information.

If you already feel comfortable about your knowledge level of basic networking, you can move on to Chapter 2. Of course, you will be missing a review of networking basics, but you will have saved a bit of reading time.

A Brief History of Network Communications

In the mid-1860s, the following scene might have taken place. A sheriff's deputy comes running into the railroad station and hurries to the desk of the Western Union telegraph operator. "Quick," he shouts to the operator, "send a message to the sheriff of Bogus City. Tell him that Butch Blunder and his gang are headed towards his town. He needs to beprepared!" With due haste, the operator sends the message in Morse code. The method used to transmit the message consisting of letters and numbers is a series of timed on-and-off pulses of electricity. Each letter or number has a unique set of short and/or long pulses. The line over which the message is sent is a single wire. The mechanism used to send and receive the message is relatively rugged-to stand up to the rough-and-ready frontier life. Although very simplistic by today's standards, the telegraph provided eastern businesses with a way to communicate with the rugged West. Let's see where communications have gone since the time that early telegram might have been sent. On February 14, 1876, Alexander Graham Bell patented the telephone-two hours before Elisha Gray, of Western Union, filed his patent. The timing on that patent filing is significant because, after a court battle, Bell was awarded not only the rights and patents to the telephone but the network of telephones that Western Union had established, including all enhancements that had been made to Bell's original designs. One hundred years later, Bell's company (later known as AT&T) was the largest company in the world.

Now, let's move our earlier scene forward in time to the late 1800s. Instead of a telegram, the deputy would just pick up a telephone headset consisting of a transmitter (the mouthpiece) and a receiver (the earpiece). He would call a central telephone operator who would then use a switchboard to transfer his call to the sheriff of Bogus City. In 1889, Almon Brown, a Kansas City undertaker, invented the Strowger switch and the telephone dial. These inventions enabled a person to dial a telephone number directly instead of having to go through an operator.

The third version of our story, taking place after the turn of the century, might have the deputy sending a written teletype warning to the sheriff of Bogus City. The original telegraph had some major drawbacks. Only one conversation at a time could cross the line. The wire used was handmade and very brittle. Installing the line was very time consuming, costly, and dangerous. The obvious solution was to develop a multiplex telegraph that would enable several operators to send and receive messages at the same time. The other goal was to create a telegraph system that did not require as much human intervention. A French inventor, Emile Baudot, made many of the necessary breakthroughs. His printing telegraph was the first to use a typewriter keyboard and enabled eight machines to share a single wire. Instead of Morse code, Baudot's machine used a five-level code that sent five pulses down the wire for each character. The machines did the encoding and decoding.

The reoccurring theme in these scenarios is, of course, our society's need to communicate information rapidly from one location to another. There's another, more important point to the three scenarios though. Have you figured it out yet? If you said, "They are all examples of networking," you'd be correct. We tend to think of electronic networks in relation to computers and cable companies that transmit radio and television broadcasts, but, as you can see from this brief history, electronic networks have been around since the mid-1800s.

At first glance, the telephone seems far removed from the computer. In reality, there is a strong interdependency between the two forms of equipment. Over the years, the telephone companies have come to rely on the computer to provide call processing, traffic routing, order tracking, and so on, while computer technology has come to rely on the telephone network to enable worldwide computer interconnection and communication.

For the most part, both the computer and the telephone rely on digital communications-those "on" and "off" pulses that Morse code relied on. However, the telephone still retains analog lines both to your home or office and to the telephone companies' switching equipment. The need to send digital signals over analog lines was the driving force in AT&T's successful invention of the telephone modem. AT&T employees also created the transistor at Bell Labs in 1948. Looking back at our earliest example of networking, the telegraph, you see an example of point-to-point communications...