CIS 3 LM The Internet

LAN, WAN, Thank you Man

We have talked a bit about how information used to be transmitted (analog,) and how technology changed this (to digital.) Now, we expand the context to look at the way computers transmit information.

In the 1960s

Since the emergence of the telephone, researchers have been looking for ways to realize and improve transmission over long distances. Ultimately, as a result of this research, computer-networking mechanisms emerged in the late 1960's.

In the 1960's, smaller and more affordable computers appeared. Corporations could afford to own more than one computer. The need to interconnect them grew.

Why are networks useful?

To transfer information without a network, operators would have to insert a big bulky disk onto one computer, and wait for it to write data onto the disk. They would then remove the disk, walk up to the other computer, and insert the disk so that it reads the information.
Another reason why networks are so important is that without a network, each computer would have to have its own printer its own storage and its own software applications. A network allows more than one computer to share the same resources (printers, faxes, software, etc.) This became possible with the introduction of LANs, which I will talk about shortly.

What is a network?

A network is a group of computers that are interconnected.

The simplest way to connect two computers is to place a communication circuit board on each of them and run a wire cable between them. On each end, the wire connects to a circuit board (this is what it looks like: ) that acts as an input/output (I/O) device. So one computer would write the data to its communication (or interface) circuit board as if it were writing data to a disk, a monitor or a printer. The destination computer would read the received data from its circuit board as if it were reading the data from a disk or a keyboard.

This method had its good and its bad:

It had the advantage that it was FAST. Because the communications circuit boards were directly connected to the computer's memory. And computer's memory is the fastest place for the computer to receive its information
It had three disadvantages however (probably among others):

It was inconvenient. To connect computer A to B, you need a pair of circuit boards (and a cable.) To connect B to C you would need another pair (and another cable.) To connect A to D, you would need yet another pair of communication boards and a cable. And so on. That was inconvenient and expensive.

If you wanted to connect two computers that were of different types, it may be impossible to find a pair of circuit boards to interconnect them.

If one of the computers is OFF, and it lies between two other computers, it would be impossible to transfer data between the two. For example if Computer A is wired to B, and B is wired to C, B would have to be ON for us to transfer any data between A and C.

LANs

LAN stands for Local Area Network. I will explain that in a minute.

Instead of connecting one computer directly to another, and so on in sequence, LAN interconnects many computers using one piece of hardware (usually the LAN cable, and sometimes types of networks use a special purpose computer called the hub. In addition, each computer on the network needs a cable to connect to it, and a circuit board (called Network Interface Card or NIC.)

Here are different types of LAN (if you wanna take notes J ):

Here the network can still function if any of those computers break down.

LANs are designed for use over a short distance (within an office suite, a floor, a whole building), but not across a city or a state. Hence their name, Local Area Network.

Because the distances are small, the electrical signals do not experience any loss inside the wire, and they remain strong. Also the signals (which travel at speeds close to the speed of light,) get to their destination faster simply because the distance is short.

Advantages of LANs:

LANs were and are great because they are inexpensive reliable and easy to install and expand in size later.

LANs also have a very important characteristic. Their speed does not depend of the speeds of the computers that are attached to it. The LAN exists independently from any of the computers attached to it. That is of course, unless it uses a hub to act as the center of the network, As you see in the third example in the figure.

LANs introduced the concept of sharing resources, which I had mentioned earlier. With LANs not only computers, but faxing machines, printers, plotters, the phone switching system, dedicated (special purpose computers) and other devices could all connect to the same network. It was no longer necessary to buy a printer for each computer. As you can see in the Atrium, All 50 or 60 computers are sharing just two printers. That is thanks to LAN technology.

Historical Note: A leading LAN technology is called Ethernet, which was introduced by Xerox.

What About WANs?

In a LAN, all we have to do to connect computers to the network is install network cards on them, and connect them using a cable wire to the network cable or hub of the LAN. As you know now, a LAN only interconnects computers that are located in one physical locality, a room, a floor or a building.

WAN, which stands for Wide Area Network, interconnects computers over long distances. WANs transmit data back and forth either over regular telephone lines using modems, or much more commonly, using dedicated long distance lines that are leased by the Telephone companies (commonly referred to as the telecom).

This kind of network emerged in the 1960s and the 1970s.

Dedicated means they do nothing but transmit data for that specific network. When we say a computer is dedicated, we mean that this computer does nothing but one specific job.

The difference between WAN and LAN, is that the Wide Area Network uses dedicated computers at each end of the network that coordinate network traffic on the transmission lines. The use of these dedicated computers keeps the network running independently of any of the computers that use it.

This is how it works. When a computer in, say, Brooklyn or Chicago wants to send data to another computer in Manhattan or Seattle, it sends the data to the dedicated WAN computer. The dedicated computer accepts the message from any of the local computers and sends it out across the transmission line towards the destination. At the other end, the other dedicated computer receives the incoming message, figures out which computer it is intended to, and delivers it.

A WAN is slower and more expensive than a LAN. Installing a WAN requires careful planning, a significant amount of hardware and software that make up the network.

There are many more LANs than WANs. (Why?)

Some Things to remember about networks with regards to the Internet:

Many different LAN and WAN technologies were developed. Each has its own idea of how to transmit data from one computer to the other. Each are developed for different levels of speed, reliability, types of services it offers, distance traveled by the data, and different types of computing needs, and different types of computers.

That is why not all LANs are compatible among themselves. Similarly, WANs are not compatible with other WANs. Finally, WANs and LANs are incompatible.

Meaning, you cannot simply connect two networks (LANs or WANs) together by running a wire between them.

You would have to use special software and/or hardware to do that.

At a certain site (e.g., a company) that has a LAN, only one of its computers can connect to a WAN. So a computer in one city could not use the printer in another city. This in many cases could be a critical disadvantage. Therefore, for a computer to be both on the LAN and on the WAN it would have to add two sets of network connections. Which is tedious and inefficient. Not to mention, that all the other computers at the LAN would have to send their data to it first, so that it would re-transfer the messages to the other end of the WAN.

So how do we connect all those networks together?

Read on.

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