CyberCollege / InternetCampus

  Updated: 05/07/2013

The Internet - 3 

 

 

 

 

Computers and

the Internet

 

 

Modems

>>Some people still use standard telephone lines to connect to the Internet.  Modem, an acronym that stands for modulation-demodulation, changes digital computer information into sounds that can be sent (modulated) and received (demodulated) via telephone lines.

Many modems, such as the one shown here, plug into a slots inside desktop computers. Laptop computers typically have them built in and they are much smaller.

>>The first modems were introduced in the 1950s. They operated at less than 100bps (bits of data per second). By today's standards this is dreadfully slow, but at that time it was fast enough for such things as text-based airline reservations and AP news wires. In those days the Internet didn't display complex pages with images, only lines of text in black-and-white.


Internet-to-Computer Connections

>>Today, most homes have some form of high-speed internet. A single computer eathernet cablecan be directly connected (hardwired) from an Internet source via an Ethernet cable.  This is the fastest and most secure type of Internet-to-computer connection.

In homes with multiple computers the signal can first be directed to a wireless router, such as the one shown below.  From there the signal can be picked up by any Wi-Fi equipped computer within about 30 meters (100 feet). WiFi Router

This communication must be two-way, so each computer must also send out a WI-FI signal.

Since anyone within the effective range can pick up both of these signals, it means that someone sitting outside of your home (or in a nearby house or apartment) could conceivably eavesdrop on anything being sent from any of your computers.

For this reason routers have a way of "securing the network" by programming a password into the router.  This password must also be used in the computers to access the router's Internet signal. 

Although so-called unsecured networks are available in places like cybercafés that offer free Wi-Fi internet service -- meaning that anyone can use them -- this is not a "feature" you want in your home or business systems. 

Today, hotels, motels, and airports provide Wi-Fi service -- often free of charge.

 

High-Speed Connections

>>If you are reading this in a library or school computer lab, the chances are that the computer is wired to the Internet with a high-speed connection  — probably a T1 line.

T1 lines are capable of transmitting digital data at more than 1.5 megabits (billions of bits) per second -- thousands of times faster than the standard analog-based dial-up modem. There are also T3 lines that can transmit data more than three times faster than T1 lines. 

Even faster are optical fiber lines that use the speed of light to transmit data. Although these are widely used for sending and receiving video, it will be some time before typical homes and businesses make the jump to fiber optic lines.

 Passwords

When it comes to protected Internet accounts, one of the biggest pains is maintaining passwords.

Passwords can be relatively easy for the wrong people to figure out -- especially if they know something about you -- your dog's name, where you were born, etc., etc.

There are even programs that will run through lists of common passwords and try to use them to get into your e-mail (as some well-known people have unfortunately found out) or to sign on to your bill pay or banking records.

Many of these secured services will lock out attempted uses of the wrong password -- and that user may be you, if you can't remember which password you used.

Although there are programs that remember all your passwords for you, the risk, of course, is in the wrong person could get access to that program.

If the system recognizes the difference between upper and lower case letters, there's added protection in using some combination: "maRgaRet." Some people suggest adding characters such as ~, < and * to, if possible, make the password even more secure.

We say "if possible" because some systems can't handle these special characters; however, all of them should be able to handle the underline character, such as in_this.

Another password approach is to use the first letters of words in a phrase you can remember -- MaryHadALittleLamb or MHALL, or something a bit more challenging.

Some password systems require at least eight characters, some of which have to be numbers and capital letters. 

Since passwords should be periodically changed, and some services force you to regularly change them, there are people that use a system that incorporates the number of the month, such as "Mar09garet."

"Margaret," by itself, would not be a good password. In addition to it being a common name -- maybe even the name of the user -- any word in a common dictionary is in the "vocabulary" of password cracking software. 

What you don't want to do is write the password down on a post-it and stick it to the computer monitor (it's been done in companies!) or even somewhere under your desk (people know this is a good place to look).


When You Delete Data It's Still There

 Your computer hard drive keeps a fairly good record of the recent sites you've visited, the pictures you've looked at, and even the files you think you've erased.

"Deleting" a file as it's normally done does not really erase it -- it only deletes the index entry that points to the original file. Assuming the data has also been erased is a little like pulling the index card from a card catalog in the library and assuming the book it points to is also gone! 

Likewise, with your computer the data is still there (for those who know how to find it) until that space if overwritten with new data.

There are programs available that will restore "deleted" files.  These are handy to have if you accidently delete a file you need. Of course, the quicker you "undelete" a file the greater the chance of completely restoring it before it's overwritten by something else.

Government computers and corporations with trade secrets use computer deletion programs that not only delete the index entry, but overwrite the original data space at least two times with randomly generated data (gibberish).

 

"Smartphones"

>> The major cell phone companies provide high-speed wireless internet for both "smart phones" and laptop computers. In the latter case this capability is generally built into the computer.

Although this approach -- often called 3G or 4G -- is much faster than the standard telephone service, it's not as fast as today's high-speed home Internet connections.

 Today's cell phones are actually miniature (and in many cases rather sophisticated) computers.  Some even have miniature hard drives.

 

Hyperlinks and Error Correction

>>When you click on a computer hyperlink you may be taken to a computer site thousands of miles away. This means that the signal may have to be routed through dozens, if not hundreds, of relay points.

If it weren't for error correction, momentary interference or interruptions could easy scramble the message. To stop this from happening data is sent and received in blocks of information. Before a block is sent it's mathematically analyzed and a checksum (a calculated value reflecting the nature of the original data) is transmitted along with the data block.

If the checksum on the receiving end doesn't match the checksum of the original data block, an error signal is transmitted to the originating source and that data block is immediately sent again.

>>You might assume that the blocks of data are all sent over the Internet using the shortest route between computers. That's not necessarily the case. In fact, depending in Internet conditions, the blocks of data within a single message can take very different geographic routes getting to their destination.

This is actually one of the strengths of the Internet. If problems develop at one or more relay points, traffic is automatically rerouted. As we will see in the next module, this feature was a cornerstone in the original Internet design.

Each block of data that is sent over the Internet carries an "address." (There will be more on this in Internet Module 4.) Once the individual data blocks arrive at their destination, they are combined in the intended sequence.


interactive test



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