How Networks Work

Computers aren't people, but they still communicate on a network similar to how a group of people communicates. That is, computers send out information that is addressed to a particular individual and then wait for a response that tells them that the message was successfully received. PCs perform this task quickly, and that's part of what makes networks so practical.

To get a better understanding of the process, imagine that Sarah is working on a homework assignment on the PC in her room. When she completes her book report, she needs a printed copy, but she doesn't have a printer connected to her PC. A printer is connected to the PC in the den, and she can use it to print out her report. The conversation between the PCs goes something like this:

"Hello den computer, this is Sarah's PC. I'm sending you this report to print."
"Okay, Sarah's PC, this is the den PC. I received the data and sent it to my printer."

Sure, that exchange sounds trivial, but it does provide a nutshell description of what's going on. At a basic level, a network functions quite simply by sending different messages as needed. The information in those messages—the data—can be something like Sarah's book report,digital images from your recent vacation, music files that you've saved on one of your PCs, or whatever other types of information you want to share.

Things are more complicated inside the inner workings of the network. In Sarah's case, for example, the printer and the den PC actually engage in quite a bit of additional conversation, discussing whether the printer is out of paper, how many pages have finished printing so far, and details of what other reports the printer has been asked to print recently. Just like the telephone network, your computer network has to keep track of who is supposed to get each bit of information and make sure that everyone else isn't drowned by a sea of data that's not intended for them. Fortunately, your network automatically handles this additional complication, and you don't have to worry about it.

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Wired Networks

A wired network is one where each computer is connected to the network through a cable. These cables typically look like a slightly fatter than normal telephone cable. Until fairly recently, wired networks were the only available option.
Wired networks offer several advantages:
1.The equipment for a wired network is inexpensive.
2.Many computers built in the past few years have a wired network adapter built in.
3.Wired networks move information somewhat faster than wireless networks.
4.Wired networks are generally more secure than wireless networks because they are harder to access physically.
On the other hand, wired networks have some disadvantages, too:
1.Running the wires from room to room can be difficult.
2.Network cables can look messy.
3.Network cables can come loose and cause the connection to fail
4.Adding more computers to a wired network might result in unexpected expense if you run out of connections on your network.
All wired networks are not the same. The most common type of wired network is called an Ethernet network, and it uses special network cables. Some wired networks make use of the existing telephone wiring or your home's power lines, but telephone line and power line networks are not as popular as the Ethernet network.

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Wireless Networks

Wireless networks use radio signals in place of wires to transmit the information among the devices on your network. Wireless is a relatively recent addition to the networking scene, but it has really taken off—especially in the home networking arena. .
Wireless networks offer several advantages compared to wired networks:
1.Installing wireless networks is easier than with wired networks, because you do not have to run cables.
2.Adding more PCs to a wireless network is easy.
3.Wireless networks give you the freedom to move to different locations within the range of the network with virtually no fuss or bother.
4.Wireless networks are rapidly becoming the most popular form of home networking, so the wireless network you set up today might have a longer useful lifetime than a wired network would.
Wireless networks do have some disadvantages, though:
1.The basic equipment required to set up a wireless network costs somewhat more than that for a simple wired network.
2.Wireless networks tend to be slower than wired networks.
3.Keeping a wireless network secure is somewhat more difficult than with a wired network.
4.Wireless networks can suffer from interference from numerous sources, such as microwave ovens and cordless phones.
5.Wireless networks might suffer from obstruction problems that severely restrict their operating distance.

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Ten Ways to Keep Your Network Healthy

As you assume the role of network administrator, remember that you need to care for your network as well as for each individual computer. Following are ten ways to keep your network healthy.

1.Protecting against Electrical Surges

An electrical surge is a sudden spate of very high voltage that travels from the electric lines to your house, and ultimately to your computer. Surges are usually caused by lightning or a return to power after a blackout.

A real surge can fry your computer.You can safeguard against spikes by plugging your computer and any attached devices such as drives, scanners,monitors, speakers, and so on, into a surge protector.

The only devices you don’t want plugged into a surge protector with your computer are printers. Read the specifications before you buy a surge protector to make sure that it’s rated for effective surge protection. (Voltage can rise by 10 volts or hundreds of volts, so make sure that the surge protector you buy can handle these extreme surges.)

In addition, because any surge received by a single computer can travel over the network cable to the other computers on your network, make sure that all the connected equipment for each of your computers is plugged into surge protectors

2.Protecting against Lightning
We’ve seen several large networks destroyed during a lightning storm, and in each case, the surge came through the telephone lines, not the electrical lines.Telephone lines are typically not protected against lightning.

The only sure protection against lightning strikes is to unplug your computers and connected equipment from both the electrical outlets and the phone jacks. Stop working. Then walk around the house and unplug other equipment with chips that could fry during a lightning storm (like your microwave oven).

3.Saving Your Computer when Power Fails
When you’re running Windows, you can’t just turn off your computer. You must initiate a shutdown procedure to shut down all your files in an orderly manner.You can keep your computers running long enough to complete an orderly shutdown of all your software and the operating system if you have an uninterruptible power supply (UPS).

A UPS is a mega-battery that you plug into the wall, and you then use the UPS outlets to connect your computer and monitor.
If your power fails, your computer draws power from the battery, giving you enough time to shut down everything.

For many home users, a UPS may be overkill. But if you live in an area that has reasonably regular power cuts due to foul weather or lousy power service, a UPS may be a good idea. If you work at home all or part of the time, a UPS is arguably
essential.

4.Fixing Low-Voltage Problems
Sometimes, the electrical voltage drops, which is called a brownout. Computers — especially their hard drives — are extremely sensitive to brownouts. Well before you see the lights flicker, your hard drive can be damaged by a brownout.

Here are some of the causes of low voltage, along with possible fixes:

-Too many appliances are plugged into the same circuit as your computer.
-An appliance that’s a voltage pig (central air conditioning, electric heating systems) kicks on, disrupting voltage throughout the house.
-Your laser printer (or powerful inkjet color printer) is plugged into the same circuit as your computer.
-The electric company is sending low voltage into your home.

You can prevent most of these problems by moving things around to different outlets. You can overcome those that you can’t prevent by purchasing a voltage regulator. A voltage regulator constantly measures the voltage coming out of the wall and brings it up to an acceptable minimum. Some uninterruptible power supplies (see the preceding section) have voltage regulation built in.

5.Preventing Static-Electricity Damage
Static electricity is responsible for more damaged computers than most people realize. One day, when some hardware component mysteriously dies, you may not realize that you zapped it yourself.

You must discharge the electricity from your body before you touch the computer or any connected devices. Touch anything metal (except an electric appliance,such as a computer or a lamp). A filing cabinet is good if one is handy. If nothing
metal is within reach, attach a metal bar to the desk or table that your computer sits on.

6.Checking Cables and Connectors
Make sure that the cables aren’t pinched or bent to the point that they can’t handle data. Have you ever sharply bent a water hose? The water stops flowing. The same thing can happen to cable. If you have excess cable, gently roll it into a circle and use a twist tie to keep it together. (Don’t tie it tightly.)

This precaution is true for all the cables in an Ethernet network, as well as for the cables between access points and your router or hub in a wireless network.Cable connectors are the weakest link in the network hardware chain. Because of
this, you should check the connectors first when your computers can’t communicate.

Here’s what to check if you wired your network with 100 BaseT or Category 5 (twisted-pair) cable:

-Make sure that the connectors are properly inserted in the NICs. Make sure that the connectors are properly inserted in the router.
-Make sure that the router is plugged in. (A router usually doesn’t have an on/off switch — if it’s plugged in, it should be working.)

Here’s what to check if you’re using wireless:
-If you’re using a splitter, make sure that the splitter is firmly positioned in the jack.

7.Checking Network Adapters
A network adapter rarely gives up, rolls over, and dies (unless you’ve had a power surge or done something dumb like stick a bobby pin in the connector). However,it’s not unheard of.

Checking Ethernet adapters

If your network adapter has a light on the back panel near the connector, the light should glow green.If you’re using Ethernet and no light is glowing and you’ve checked the connectors and the cable, the only way to check the network adapter is to replace it.

If the new device works, the old one was bad. If the new device doesn’t work, recheck your connectors and cable. Take the new device back to the store and get a credit.If your network adapter has two little light bulbs and the red one is glowing, it’s working but isn’t receiving or sending data. You can be fairly sure that you have a connector or cable problem.

Checking wireless adapters

If you have a wireless network, run your signal strength utility (Programs USR WLAN USR Adapter Wireless LAN Configuration Utility) and see if you’re getting a signal and if the adapter is functioning properly.

If you suddenly have problems with signal strength, or your network just ceases to function and you can’t figure out why, ask yourself whether you have any large appliances running at the same time you’re trying to use your network. Items like microwave ovens, washing machines, and especially anything with a large electrical motor, can cause interference.

Usually, for these appliances to cause trouble with your network, they have to be physically very close to an access point or adapter. If you have multiple 802.11 devices from different companies all trying to work in the same area, you could experience signal problems.

Using the U.S. Robotics Wireless LAN Configuration Utility to help reposition your access point, computer, or the offending electrical appliance should get you network functioning again. Just move things around a bit (usually a few feet will do the trick) until the signal looks good again. We think it’s pretty cool that the wireless networking hardware comes with its own built-in test bench!

8.Monitoring Monitors
Monitors require some special attention, and too many people maul and mishandle them. By no coincidence at all, those same people are the ones who have to buy new monitors more frequently than should be necessary.

A monitor’s screen attracts and collects dust — it actually sucks dust out of the air.You can’t avoid monitor dust. Remove the dust by wiping the screen with a soft,dry cloth. You’re best to do this with the monitor turned off. (Static electricity, which is responsible for attracting the dust, can build up to damaging levels when you rub the screen.)

If you want to use the bottle of window cleaner that you keep around the house,spray it on a cloth, not on the monitor; the monitor isn’t sealed properly to avoid leaks. Then wipe the moistened cloth across the screen.

9.Protecting Printers
You should perform a few maintenance chores regularly to make sure that your printed documents look terrific and your printers perform without errors:

-Don’t overfill paper trays — doing so results in printer jams. If you have to clean up a printer jam, unplug the printer. Never yank on the jammed paper. Pull it steadily and gently.
-Always clean a laser printer when you change toner cartridges, following the directions that come with the cartridge. -Keep printers covered when they aren’t in use. Dust is their biggest enemy.
-Use paper that’s compatible with your printer. (Check the documentation that came with your printer.)

Besides protecting your printer, you also need to protect your computer from your printer, especially if you use a laser printer or a powerful color inkjet printer. These printers use a lot of power. If they’re on the same circuit as your computer, you’re probably causing minor brownouts for the computer, which can harm your hard
drive and your data.

10.Using Antivirus Software
You know if one kid in kindergarten gets the chicken pox, nearly every other kid will too? Computer networks are similar. If one computer has a virus, other computers in your network probably will too.

The very nature of a network — allowing easy sharing of files and folders — means that one infected computer can
easily infect others. Viruses can cause no damage at all, or can be devastating,causing complete loss of all data on a hard drive.

Fortunately, preventing such mishaps is easy. Antivirus software is essential for your network. Each computer on your network needs to have antivirus software installed and regularly updated. With antivirus software installed, you can keep all
the computers on your network happy and healthy.


Backing Up
Loss of data can occur because of, among other things, a virus, a power surge, or plain old hardware failure. Of course, with antivirus software installed and surge protectors on your computers, the chances of data loss are small. However, backing up your data means that you’re protected if the unthinkable should happen.

You can purchase backup programs with sophisticated server features, enabling you to specify a location, such as a shared removable drive on your network for all your computers to back up to.

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LAN Tips, Protecting Shared Documents (1)

This section heading might seem like an oxymoron. I mean, if you want to protect a document and keep it private, why would you share it in the first place? Answer: Perhaps you occasionally work at other computers in the LAN and want to access some of your documents at other computers. You just don’t want anyone else to have access to the document from a shared computer.

The simplest way to do this is to password-protect the document as you save it to a shared folder. The exact technique for password-protecting a shared document varies from one program to the next. I cannot even say for certain that all programs will support it.

Using Microsoft Excel as an example, however, let’s say you’re about to save a worksheet that you want to access from other computers in the LAN, but keep other people out of it. Choose File → Save As and then choose Shared Documents from the Save in drop-down list to make the file’s icon available from all computers in the LAN. Prior to clicking that Save button, however, click Tools in the Save As dialog box and choose General Options.

To prevent others from opening the file, enter a password for Password to open. Needless to say, you don’t want to forget this password or you won’t be able to open the document yourself — ever! Use the same password for every document. If you start making them up on a document-by-document basis — trust me on this — you’ll wish you hadn’t. (The voice of experience here.) Click OK and then click Save to save the document.

Other users can see the document’s icon. When they attempt to open the document, however, they’ll be prompted for the password. If they don’t enter the correct password, the file won’t open.

If you want others to be able to see, but not change, the document, leave the Password to open option blank and enter a Password to modify instead. Upon opening the file, other users are prompted for the password to make modifications. If they can’t enter the appropriate password, they can open the document only in read-only mode. This, in turn, prevents them from changing the document.

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Some people who cause security problems and why

For the first few decades of their existence, computer networks were primarily used by university researchers for sending e-mail and by corporate employees for sharing printers. Under these conditions, security did not get a lot of attention. But now, as millions of ordinary citizens are using networks for banking, shopping, and filing their tax returns, network security is looming on the horizon as a potentially massive problem.

Security is a broad topic and covers a multitude of sins. In its simplest form, it is concerned with making sure that nosy people cannot read, or worse yet, secretly modify messages intended for other recipients. It is concerned with people trying to access remote services that they are not authorized to use. It also deals with ways to tell whether that message purportedly from the IRS saying: Pay by Friday or else is really from the IRS and not from the Mafia.

Security also deals with the problems of legitimate messages being captured and replayed, and with people trying to deny that they sent certain messages.

Some people who cause security problems and why

1.Student,to have fun snooping on people's email
2.Cracker,to test out someone's security sistem or steal data
3.Sales rep,to claim to represent Europe
4.Businessman,to discover a competitor's strategic marketing plan
5.Ex-Employee,to get revenger for being fired
6.Accountant,to embezzle money from a company
7.Stockbroker,to deny a promise made to a customer by e-mail
8.Con man,to steal credit card numbers for sale
9.Spy,to learn an enemy's military or industrial secrets
10.Terrorist,to steal germ warfare secrets

Most security problems are intentionally caused by malicious people trying to gain some benefit, get attention, or to harm someone. A few of the most common perpetrators are listed above. It should be clear from this list that making a network secure involves a lot more than just keeping it free of programming errors. It involves outsmarting often intelligent, dedicated, and sometimes well-funded adversaries. It should also be clear that measures that will thwart casual adversaries will have little impact on the serious ones.

Police records show that most attacks are not perpetrated by outsiders tapping a phone line but by insiders with a grudge. Consequently, security systems should be designed with this fact in mind.

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Securing Windows Machine

To reduce the possibility for intruder to spoof into the network is necessary to a static entry in Address Resolution Protocol (ARP) table. ARP table contains a list of IP address with its corresponding MAC address listen by our machine.
ARP Table is normally dynamically set through Address Resolution Protocol (ARP). Shown in the example, by entering the command

arp –a

the operating system will gives the list of IP address with its corresponding MAC address. It is shown in the top command that the type of entry is dynamic. An intruder can spoof into the network and pretend to have the particular IP address.

Such condition can be circumvent by setting a certain IP address to a fixed MAC address. It is can be done through,

arp –s ip.ad.dre.ss mac-add-res-ss

For example,

arp –s 192.168.0.32 00-50-ba-62-f7-e6

To see if the entry is a static entry, we can enter “arp –a” command again and check if the type of static.

For those who use Windows 98, you may have to look for personal firewall software to secure your machine in WiFi infrastructure. Such software can be easily find through Google search.

For those who use Windows XP, you are in luck as XP has a built-in firewall facility. The firewall can be access through Start -> Control Panel -> Network Connections -> Local Area Network -> Properties -> Advanced -> Settings.

We have to check “Protect my computer and network by limiting or preventing access to this computer from the Internet” before we can click firewall Settings button.

In Firewall Settings page, we can check which services we want our firewall will allow Internet users to access into our computer.We can also Add the service if it is not readily available on the Firewall.A facility to configure the Internet Control Message Protocol (ICMP), used in various program such as ping, can also be controlled through ICMP facility.

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