The Flintstones are a cartoon family that, according to the cartoon, lived in prehistoric times. Because I want to discuss the thought process behind some imaginary initial networking standards, the Flintstones seem to be the right group of people to put in the example.
Fred is the president of FredCo, where his wife (Wilma), buddy (Barney), and buddy's wife (Betty) all work. They all have phones and computers, but they have no network because no one has ever made up the idea of a network before. Fred sees all his employees running around giving each other disks with files on them, and it seems inefficient. So, Fred, being a visionary, imagines a world in which people can connect their computers somehow and exchange files, without having to leave their desks. The (imaginary) first network is about to be born.
Fred's daughter, Pebbles, has just graduated from Rockville University and wants to join the family business. Fred gives her a job, with the title First-Ever Network Engineer. Fred says to Pebbles, "Pebbles, I want everyone to be able to exchange files without having to get up from their desks. I want them to be able to simply type in the name of a file and the name of the person, and poof! The file appears on the other person's computer. And because everyone changes departments so often around here, I want the workers to be able to take their PCs with them and just have to plug the computer into a wall socket so that they can send and receive files from the new office they moved to. I want this network thing to be like the electrical power thing your boyfriend, Bam Bam, created for us last year—a plug in the wall near every desk, and if you plug in, you're on the network!"
Pebbles first decides to do some research and development. If she can get two PCs to transfer files in a lab, then she ought to be able to get all the PCs to transfer files, right? She writes a program called Fred's Transfer Program, or FTP, in honor of her father.
The program uses a new networking card that Pebbles built in the lab. This networking card uses a cable with two wires in it—one wire to send bits and one to receive bits. Pebbles puts one card in each of the two computers and cables the computers together with a cable with two wires in it. The FTP software on each computer sent the bits that comprised the files using the networking cards. If Pebbles types a command like ftp send filename, the software transfers the file called filename to the computer at the other end of the cable. Figure 1-3 depicts the first network test at FredCo.
Figure 1-3 Two PCs Transfer Files in the Lab
Network Card Network Card
Figure 1-3 Two PCs Transfer Files in the Lab
Network Card Network Card the dashed lines represent the two wires inside the cable. The Network cards reside inside the computer.
the dashed lines represent the two wires inside the cable. The Network cards reside inside the computer.
Note that because each networking card uses wire 1 to send bits and wire 2 to receive bits, the cable used by Pebbles connects wire 1 on PC1 to wire 2 on PC2, and vice versa. That way, both cards can send using wire 1, and it will enter the other PC on the other PC's wire 2.
Bam Bam happens by to give Pebbles some help after hearing about the successful test. "I'm ready to start deploying the network!" she claims. Bam Bam, the wizened one-year veteran of FredCo who graduated from Rockville U. a year before Pebbles, starts asking some questions. "What happens when you want to connect three computers together?" he asks. Pebbles explains that she can put two networking cards in each computer and cable each computer to each other. "So what happens when you connect 100 computers to the network—in each building?" Hmmm____Pebbles then realizes that she has a little more work to do. She needs a scheme that allows her network to scale to more than two users. Bam Bam goes on, "We ran all the electrical power cables from the wall plug at each cube back to the broom closet. We just send electricity from the closet out to the wall plug near every desk. Maybe if you did something similar, you can find a way to somehow make it all work."
With that bit of input, Pebbles has all the inspiration she needs. Emboldened by the fact that she had already created the world's first PC networking card, she decides to create a device that will allow cabling similar to Bam Bam's electrical cabling plan. Pebble's solution to this first major hurdle is shown in Figure 1-4.
Figure 1-4 Star Cabling to a Repeater
Pebbles follows Bam Bam's advice about the cabling. However, she needs a device into which she can plug the cables—something that will take the bits sent by a PC, and reflect, or repeat, the bits back to all the other devices connected to this new device. Because the networking cards send bits using wire 1, Pebbles builds this new device so that when it receives bits coming in wire 1 on one of its ports, it will repeat the same bits—but out wire 2 on all the other ports, so the other PCs get those bits on the receive wire. (Therefore, the cabling does not have to swap wires 1 and 2—this new device takes care of that.) And because she is making this up for the very first time in history, she needs to decide on a name for this new device: She names the device a hub.
Before deploying the first hub and running a bunch of cables, Pebbles does the right thing: She tests it in a lab, with three PCs connected to the world's first hub. She starts FTP on PC1, transfers the file called recipe.doc, and sees a window pop up on PC2 saying that the file was received, just like normal. "Fantastic!" she thinks—until she realizes that PC3 also has the same pop-up window on it. She has transferred the file to both PC2 and PC3! "Of course!" she thinks. "If the hub repeats everything out every cable connected to it, then when FTP sends a file, everyone will get it. I need a way for FTP to send a file to a specific PC!"
At this point, Pebbles thinks of a few different options. First, she thinks that she will give each computer the same name as the first name of the person using the computer. She will then change FTP to put the name of the PC that the file was being sent to in front of the file contents. In other words, to send her mom a recipe, she will use the ftp Wilma recipe.doc command. So, each PC will receive the bits because the hub repeats the signal to everyone connected to it, but only the PC whose name is the one in front of the file should actually create the file. Then her Dad walks in: "Pebbles, I want you to meet Barney Fife, our new head of security. He'll need a network connection as well—you are going to be finished soon, right?"
So much for using first names for the computers: There are now two people named Barney at FredCo. Pebbles, being mathematically inclined and in charge of creating all the hardware, decides on a different approach. "I'll put a unique address on each networking card—a 4-digit decimal number," she exclaims. Because Pebbles created all the cards, she will make sure that the number used on each card is unique. Also, with a 4-digit number, she will never run out of unique numbers—she has 10,000 (104) to choose from and only 200 employees at FredCo.
By the way, because she's making all this up for the very first time, she calls these built-in numbers on the cards addresses. When anyone wants to send a file, they can just use the ftp command, but with a number instead of a name. For instance, ftp 0002 recipe.doc will send the recipe.doc file to the PC whose network card has the address 0002. Figure 1-5 depicts the new environment in the lab.
Figure 1-5 The First Network Addressing Convention
Figure 1-5 The First Network Addressing Convention
Now, with some minor updates to the Fred Transfer Program, the user can type ftp 0002 recipe.doc to send the file recipe.doc to the PC with address 0002. Pebbles tests the software and hardware in the lab again, and only PC2 receives the file when it is sent to PC2. When she sends the file to 0003, only PC3 receives the file. She's now ready to deploy the first computer network.
Pebbles now needs to build all the hardware needed. She first creates 200 network cards, each with a unique address. She installs the FTP program on all 200 PCs and installs the cards in each PC. Then she goes back to the lab and starts planning how many cables she will need and how long each cable should be. Then she realizes that she will need to run some cables a long way. Even if she puts the hub in the bottom floor of building A, the PCs on the fifth floor of building B will need a really long cable to connect to the hub. Cables cost money, and the longer the cable is, the more expensive the cable is. Besides, she has not yet tested the network with longer cables; she has been using cables that are only a couple of meters long.
Bam Bam happens by and sees that Pebbles is stressed. Pebbles vents a little: "Daddy wants this project finished, and you know how demanding he is. And I didn't think about how long the cables will be—I'll be way over budget. And I'll be running cables for weeks!" Bam Bam, being a little less stressed, having just come from a workout during lunch break at the club, knows that Pebbles already has the solution—she was too stressed to see it. Of course, the solution is not terribly different from how Bam Bam solved a similar problem with the electrical cabling last year. "Those hubs repeat everything they hear, right? So, why not make a bunch of hubs. Put one hub on each floor, and run cables from all the PCs. Then run a cable from the hub on each floor to a hub on the first floor Then, run one cable between the two main hubs in the two buildings. Because they repeat everything, every PC should receive the signal when just one PC sends, whether they are attached to the same hub or are four hubs away." Figure 1-6 depicts Bam Bam's suggested design.
Figure 1-6 Per-Floor Hubs, Connected Together rrrrrrrrr
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