Hey rm green and in Impact Font!
UNIT 29: Data Transmission Systems, Internet Service Providers (ISP) and Virus Table of Contents
UNIT 29: Data Transmission Systems, Internet Service Providers (ISP) and Virus
1.0 Introduction
One of the most confusing issues for computer users is the excitement that is going on between different Internet access providers. or ISPs as they are called. Dial-up modem, cable modem, digital subscriber lines (DSL), and satellite access are all options available to the average consumer, but which is the fastest of all these? In this unit, we'll look at each of these Internet access methods in depth to show you the advantages and disadvantages of each.
2.0 Objectives
At the end of this unit you will be able to:
Explain how modems work;
Identity the various data transmission system;
Choose an ISP;
Identify the problems of virus and how to solve it.
3.1 Some Background
Internet access speeds are often referred to in k, or kps. KPS stands for kilobits per second, and stands for a specific amount of data sent through a signal. In order to understand, you must first know the basics of the computer language.
Computers use a language of O's and Ps. A bit is a single 0 or 1 in the computer language. When you put 8 bits together, you get 1 byte. 1 byte is the equivalent of 1 character. For example, when you type the letter. A, the computer sees the "A" as 1 byte of information.
When you talk about file storage, you talk in K, which is kilobyte. 1K is equal to 1024 bytes.
When you talk about data transfer like modems, you talk in kbps, or kilobit per second. lk is equal to 1024 bits, or 128 bytes. This is why a 100K file isn't downloaded in 2 seconds on a 56k modem. It actually takes 8 times as long, because 100K is equal to 800k.
3.2 Dial-Up Modem
Since the earliest days of computers, the desire to hook up two systems over long distances was always a challenge. In order to do this, a method of sending a signal over a normal telephone line had to be found. This process is called MOdulation/DEMOdulaltion, short-form to modem.
Modulation and demodulation is required because telephone lines use analog signalling where computers are digital. In order for a computer to talk across a phone line, it first had to change it's signal into a format the phone could understand. This is called modulation. The process of converting the signal back to digital is called demodulation.
Modems are serial connections. That means that they send one signal at a time over the telephone line. In the early days of modems, you could actually talk on the same line to the person on the other computer while the modem was sending. As modems became faster, they regimen more and more space on the phone line to send signals, and ended this ability.
Exercise 1
State the main functions of a modem.
Modem is made up of modulator and demodulators. In order for a computer to talk across a phone line, it first had to change it's signal into a format the phone could understand (modulation). And since the computer signals are digital, the signals from the phone are connected back to digital (demodulation).
Most people use 56k modems to connect to the Internet, although older systems still have 33.6k or 28.8k modems in them. The number (such as 56) is the fastest transfer speed that a modem can send and receive information. A 56k modem can send 56 kilobits of information per second, or about 7Kilobytes per second.
Under the best circumstances with a 56k modem, you will get about 5.5Kbps transfer. This means a 100K file will take about 18 seconds. Noisy phone lines, bad switches, and cheap modems will decrease your chances of attaining these speeds, and speed varies by intemet access provider.
32.1 Cable Modems
When looking for faster data transfer, networking specialists found an easy method of using existing technology to speed up access. This is called a cable modem, and uses the cable TV wire already in your home. Since many networks already run on a cable very similar to cable TV wire, it was just a matter of adapting the signal so the computer could understand.
Cable is considered broadband internet access, because everyone on the cable network sees the signal to and from your computer. This varies from telephone signals that are only seen on your phone line, called baseband transmissions. The advantage of broadband transmissions is that they don't have to dedicate a wire to you and you alone; everyone on the network can share the same wire. The other advantages of broadband is that it's always on, whether you are at your computer or not.
Exercise 2
Explain the difference between broadband and baseband transmission.
In broadband transmission everyone on the cable network and the signal too are from your computer while in the baseband transmission the signals are only seen on your telephone line.
Cable access is sold in many different ways. Most times, you buy it with a limitation on the amount of bandwidth, or the amount of data per second, they allocate to you. This can range from 128kbps to 512bps.
Basically, you pay more for faster service.
The average cable plan offers about 256kbps transfer. Some will offer faster access at a premium price, but as more and more people sign up, the data rates tend to fall to slower levels than the 512kbps packages many providers offer. So for argument's sake, we're going to assume you get steady 256kps transfer. Our 100K file now takes only 3.1 seconds to download.
3.2.3 Digital Subscriber Lines (DSL)
In the middle-90's. technicians at Bell Laboratories discovered a new way to use existing phone line to transfer data at a faster rate. They used a combination of existing technologies with the fact that analog phone line only use 2% of the bandwidth available to them. This technology is called DSL.
What inventors did was essentially figure out a way to use the 95% of the bandwidth available on your phone for data transfer. From our dial-up modem's sections, POTS (Plain Old Telephone Systems) work on an analog signal. The wires that carry the signal work for both analog and digital signals. All they had to do was find a way to transfer both at once.
DSL access works by separating the analog and digital signals at your house, allowing the digital and analog signals to co-exist over the distance from your house to the phone company's office, and vice versa. A packet sniffer separates data packets from analog signals. and routes the signals to the proper equipment. This allows you to talk on the same phone line as you're using to access the internet.
DSL comes in many varieties and many speeds. You may have heard of it as ADSL, VDSL,
Exercise 6
State the two phases of a virus and the solution to these virus attacks.
As indicated above, virus have two specific phases which are, infection phase and active phase. The only solution to a virus effect is the use of anti-virus software to clean the infected machine.
4.0 Conclusion
In order for a computer to talk across a phone line, modem is required because telephone lines use analog signalling, where computers are digital. DSL access works by separating the analog and digital signals at your house, allowing the digital and analog signals to co-exist over the distance from your house to the phone company's office, and vice versa. For those of us in areas that are not serviced by cable and ADSL. Dial-up access will continue to be our only method of connection. Well, until wireless services are available nationwide.
Half of the computers on the internet either have viruses, or are a prime target for one. Only you can protect your computer, so take the time to install anti-virus software and keep your virus definition file up to date.
5.0 Summary
In this unit, we considered the various methods of Internet access, with respect to the access speeds with a view of choosing an ISP. The advantages and disadvantages of the methods were considered.
The effect of viruses, worms, and Trojans and how to protect our computers from them were discussed.
6.0 References and Suggestion for Further Reading
Computer Networking http://compnetworking.about.com Widernet Project, http//www.widernet.org
Developing HTML http:www.davesite.com/webstation/html/
7.0 Tutor-Marked Assignment
Question
Discuss the four various systems of data transmission stating their advantages and disadvantages.