computers

Content
Content 1
Channels of communication 2
What are ‘telecommunications’? 2
What can you do with a modem? 2
Modems 2
What do you need to telecommunicate? 2
Local bulletin boards 2
Online service providers 3
Security and privacy on the Internet 3
Security on the Web 3
E-mail privacy 4
Network security 4
Virus protection 4
Network configurations 4
WANs and worldwide communications 5
New technologies 6
Hackers! 7Channels of communication
What are ‘telecommunications’?
This term refers to the transmission of information over long distances using the telephone system, radio, TV satellite or computer links. Examples are two people speaking on the phone, a sales department sending a fax to a client or someone reading thhe teletext pages on TV But in the modern world, telecommunications mainly means transferring information from one PC to another via modem and phone lines (or fibre-optic cables).What can you do with a modem?
A modem is your computer’s link to the external world. With a modem you can exchange e-mail and files with friends and colleagues; you can access the Web and search for information about the stock market, current affairs, entertainment, etc..; you can participate in newsgroups and live coonversations; you can make bank transactions and buy things from the comfort of your home. You can also access your office from your computer at home or your laptop in a hotel room.Modems
Your PC is a digital device (it works wi

ith strings of 1s and 0s). However, the telephone system is an analogue device, designed to transmit the sounds and tones of the human voice. That’s why we need a modem – a bridge between digital and analogue signals. The word ‘modem’ is an abbreviation of MOdulator/DEModulator. When a modem modulates, it sends very rapid on/off pulses. The computer on the other end translates (demodulates) those signals into intelligible text or graphics. Modem transmission speeds are measured in kilobits per second. Typical speeds on 28.8, 33.6 and 56 kbps.
Today a lot of companies find it more efficient to have some employees doing their work at home. Using a modem, they transfer their work into the office where it is printed and distributed. The list off applications is endless.What do you need to telecommunicate?
You just need a PC (or a terminal), a modem 30 connected to the computer and the telephone line, and communication software. Once you have installed and configured your modem, you can communicate with people through bulletin boards and online services.Local bulletin boards
Bulletin board systems (BBS) are frequently free because they are run by enthusiasts and sponsored by user groups or small businesses. The first time you make a BBS connection you are re
equired to register your name, address, phone number and other information such as the kind of computer and modem you are using. The person who administers the BBS is called sysop (system operator). You can use a BBS to download artwork, games and programs, or you can participate in ongoing discussions. You can also upload (send) programs, but make sure they are shareware or public domain programs.Online service providers
To gain access to the Internet you must first open an account with an Internet service provider (ISP) or a commercial online service provider. Both offer Internet access, but the latter provides exclusive services.
• Internet service providers usually offer access to the Web and newsgroups, an e-mail address, a program to download files from FTP sites, and IRC software so that you can have live chats with other users. Most ISPs charge a flat monthly or annual fee that gives you unlimited access to the Internet.
• The main commercial online services are America Online, CompuServe, Prodigy and Microsoft Network. They differ from dedicated ISPs in two ways: (1) they use a smooth, easy-to-use interface, and (2) they have extra services for members only (but they charge higher prices). For example, they offer airline reservations, professional forums, on
nline shopping and stories for children. They also let you search their online encyclopaedias and special databases.Security and privacy on the Internet
There are a lot of benefits from an open system like the Internet, but we are also exposed to hackers who break into computer systems just for fun, as well as to steal information or propagate viruses. So how do you go about making online transactions secure?Security on the Web
The question of security is crucial when sending confidential information such as credit to card numbers. For example, consider the process of buying a hook on the Web. You have to type your credit card number into an order form which passes from computer to computer on its way to the online bookstore. If one of the intermediary computers is infiltrated by hackers, your data can be copied. It is difficult to say how often this happens, but it’s technically possible.
To avoid risks, you should set all security alerts to high on your Web browser. Netscape Communicator and Internet Explorer display a lock when the Web page is secure and allow you to disable or delete ‘cookies’.
If you use online bank services, make sure your bank uses digital certificates. A po
opular security standard is SET (secure electronic transactions).E-mail privacy
Similarly, as your e-mail message travels across the net, it is copied temporarily on many computers in between. This means it can be read by unscrupulous people who illegally enter computer systems.
The only way to protect a message is to put it in a sort of ‘envelope’, that is, to encode it with some form of encryption. A system designed to send e-mail privately is Pretty Good Privacy, a freeware program written by Phil Zimmerman.Network security
Private networks connected to the Internet can be attacked by intruders who attempt to take valuable information such as Social Security numbers, bank accounts or research and business reports.
To protect crucial data, companies hire security consultants who analyse the risks and provide security solutions. The most common methods of protection are passwords for access control, encryption and decryption systems, and firewalls.Virus protection
Viruses can enter a PC through files from disks, the Internet or bulletin board systems. If you want to protect your system, don’t open e-mail attachments from strangers and take care when downloading files from the Web. (Plain text e-mail alone can’t pass a virus.)
Remember also to update your anti-virus software as often as possible, since new viruses are being created all the time.Network configurations
A network is a group of devices (PCs, printers, etc.) or ‘nodes’ connected by communications circuits so that users can share data, programs and hardware resources. A network has two main elements: the physical structure that links the equipment and the software that allows communication.
The physical distribution of nodes and their circuits is known as network ‘topology’ or ‘architecture’. The software consists of the protocols, i.e. the rules which determine the formats by which information may be exchanged between different systems. We could say that cables and transceivers (the architecture) allow computers to ‘hear’ one another, while the software is the ‘language’ that they use to ‘talk’ to one another over the network.
As regards the cables, they consist essentially of the transceiver – the hardware that sends and receives network signals. At present the most widely used transceivers are Token Ring, Ethernet and LocalTalk. Token Ring is the most common method of connecting PCs and IBM mainframes. Most Token Ring adapters transmit data at a 25 speed of 16 megabits per second. With Ethernet, data is transmitted at 1IX) Mbits/sec. Ethernet provides a very robust, trouble-free architecture with good levels of performance. In this regard, Ethernet is the best solution for fast and intensive activity.
LocalTalk transceivers are the cheapest of all because they are directly included in each Macintosh. However, they’re a bit slow, which is why most Macs come with built-in Ethernet.
As for protocols, these are rules which describe things like transmission speed and physical interfaces. The Token Ring protocol avoids the possibility of collisions. ‘1’o transmit data, a workstation needs a token, and as there is only one token per network, holding one guarantees sole use of the network. With Ethernet there are other options, of which TCP/IP (Transmission Control Protocol/Internet Protocol) is perhaps the most useful since it allows different operating systems to communicate with each other. With regard to LocalTalk networks, they use AppleTalk protocols. The Macintosh operating system includes the AppleTalk manager and a set of drivers that let programs on different Macs exchange information.
LANs can be interconnected by gateways. These devices help manage communications and control traffic on large networks. They change the data to make it compatible with the protocols of different networks.WANs and worldwide communications
For long-distance or worldwide communications, computers and LANs are usually connected into a wide area network (VAN) to form a single, integrated network. Two good examples of wide area networks are Internet and Arpanet. They transfer data and e-mail for university researchers and academics, commercial groups, military installations and ordinary people.
Networks can be linked together by either telephone lines or fibre-optic cables. For example, ISDN (integrated services digital network) is an international standard for transmitting digital text, sound, voice and video data over telephone lines. On the other hand, FDDI (fibre distributed data interface) is an optical-fibre network. This new standard transmits data at great speed – 100 megabits per second.
Modern telecommunications use fibre-optic cables because data can be transmitted at a very high speed through the extremely wide bandwidths of glass fibres. The fibre system operates by transmitting light pulses at high frequencies along the glass fibre. This offers considerable advantages: (i) the cables require little physical space; (ii) they are safe because they don’t carry electricity; (iii) they avoid electromagnetic interference.
Networks on different continents can also be connected via satellite. Computers are connected by a modem either to ordinary telephone wires or fibre-optic cables, which are linked to a dish aerial. This aerial has a large concave reflector for the reception and sending of signals. Then, when signals are received by the satellite, they are amplified and sent on to workstations in another part of the world.New technologies
1 Smart phones for, sending and receiving voice, e-mail, and Internet data are already available. One example MobileAccess, the wireless phone from Mitsubishi. The software from Unwired Planet connects you to a server, displaying a directory of databases and information services.
You can connect MobileAccess to your laptop and use its modem to access the Internet. The technology is based on the cellular digital packet data (CDPD) protocol.
2 Internet TV sets allow you to surf the Web and have c-mail while you are watching TV or vice versa. Imagine watching a film on TV and simultaneously accessing a Web site where you get information on the actors in the film. This is ideal for people who are reluctant to use PCs but are interested in the Internet.
WebTV was the first company which brought Internet services to TV viewers through a set-top computer box. Another option is WorldGate’s technology, which offers the Internet through cable TV.
The model built by OEM Metec integrates a complete Windows PC in a TV set. The next generation of Internet-enabled televisions will incorporate a smart-card for home shopping, banking and other interactive services.
3 Virtual reality lets people interact with artificial objects and environments through three-dimensional computer simulation. In a VR system, you are hooked to a computer through a controlling device, such as a glove, and head-mounted displays give you the feeling of being propelled into an artificial three-dimensional world. The computer brings to life events in a distant, virtual world using databases or real-time objects and sounds. Your senses are immersed in an illusionary; yet sensate, world.
VR can be applied to anything from video games, testing a motor vehicle, visiting a virtual exhibition, to checking out imaginary kitchen designs.
4 Video teleconferencing is a new technology that allows organizations to create ‘virtual’ meetings with participants in multiple locations.
A video teleconferencing system combines data, voice and video.
Participants see colour images of each other, accompanied by audio, and they can exchange textual and graphical information.
In video teleconferencing, images are captured by computer-mounted cameras. Video processors digitize and compress the images, which are transmitted over a network bidirectionally. Data and sound travel via telephone lines.Hackers!
Sept ‘70 John Draper, also known as Captain Crunch, discovers that the penny whistle offered in boxes of Cap’n Crunch breakfast cereal perfectly generates the 2,600 cycles per second (Hz) signal that AT&T used to control its phone network at the time. He starts to make free calls.
Aug ‘74 Kevin Mitnick, a legend among hackers, begins his career, hacking into banking networks and destroying data, altering credit reports of his enemies, and disconnecting the phone lines of celebrities. His most famous exploit – hacking into the North American Defense Command in Colorado Springs – inspired War Games, the 1983 movie.
Jul ‘81 Ian Murphy, a 23-year-old known as Captain Zap on the networks, gains instant notoriety when he hacks into the White House and the Pentagon.
Dec ‘87 IBM international network is paralysed by hacker’s Christmas message.
Jul ‘88 Union Bank of Switzerland ‘almost’ loses £32 million to hacker-criminals. Nicholas Whitely is arrested in connection with virus propagation.
Oct ‘89 Fifteen-year-old hacker cracks US defence computer.
Nov ‘90 Hong Kong introduces anti-hacking legislation.
Aug ‘91 Israelis arrest 18-year-old for hacking foreign banking and credit card networks.
Jul ‘92 In New York, five teenagers are charged with breaking into computer sytems at several regional phone companies, large firms and universities.
Dec ‘92 Kevin Poulsen, known as ‘Dark Dante’ on the networks, is charged with stealing tasking orders relating to an Air Force military exercise. He is accused of theft of US national secrets and faces up to 10 years in jail.
Feb ‘97 German Chaos Computer Club shows on TV the way to electronically obtain money from bank accounts using a special program do the Web.
May ‘98 Computer criminals propagate a lot of viruses through the Internet.

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