Communication channels

A communication channel is a trans­mission path for electrical or optical sig­nals. All communication channels use the medium of electromagnetic waves, such as radio waves, light waves, and microwaves, which differ only in their frequency. Frequency is a measure of the number of waves that are transmit­ted per second and is measured in hertz.) By converting one kind of wave, such as sound, into another, such as radio, waves can be made to carry conversations, data, and video around the world. There are two categories of communication channels: wired and wireless.

Several different types of wire are com­monly used to implement communica­tion channels. The simplest and least expensive medium is called twisted-pair wire. The wires that connect your tele­phone to the local telephone office are an example of twisted-pair wires. An­other common medium is the coaxial cable, which is wire surrounded by a flexible metallic shielding. A familiar ex­ample is found in cable TV connections. Coaxial cables have much higher capac­ity than do twisted-pair wires but are more expensive. The newest form of cable that is replacing coaxial cable is called a fibre-optic cable, which is made of optical fibres. An optical fibre is a filament of glass about the same size in diameter as a human hair. It uses light instead of electricity to transmit informa­tion. In theory, a fibre-optic cable can replace a wire in any application.

The second category of communication channel uses waves transmitted through open space. This category includes mi­crowaves, light waves, and radio waves.

An early form of wide-area wireless communication used microwaves to transmit and receive information. This type of system is capable of transmitting at higher capacities than are twisted-pair wires (twisted pair) or most coaxial cables. However, microwave systems are expensive be­cause they require relay stations with repeater antennas every 20 to 30 miles (32 to 48 kilometres). Relay stations are needed because microwave systems can only transmit data on a “line-of-sight” path. Each station is placed in line with the next, amplifiesthe signal received, and transmits it to the next relay station in the chain.

Infrared light waves are used as a communication channel, but only for short distances. Your television or VCR remote-control device is an example of an infrared communication channel. In­frared technology is also used in local-area networks to connect computers and devices in the same office. Infrared is also a popular wireless medium for por­table hand-held computers. For ex­ample, two users of infrared-equipped handheld computers could exchange electronic business cards by simply pointing the devices at one another, or connect to a local-area network in the same room to send and receive messages.

Radio waves are the most common wireless communication medium. They are transmitted by antennas, which can send or receive the waves. For local-area networks, one technology is called spread-spectrum radio, which is similar to the technology used in cordless tele­phones and garage door openers.

In the case of metropolitan-area net­works, one antenna is located in the mobile device, the other at the base sta­tion in the geographic cells. In wide-area networks, one antenna is located on the ground, the other in a satellite. Some communication satellites are placed in orbit 22,300 miles (35,680 kilometres) above the Earth’s surface. At this orbit, called geosynchronous, it takes exactly 24 hours to circle the earth, so the satel­lite appears to be stationary to the ground station. Television programs, telephone calls, and data can be trans­mitted from one continent to another using geosynchronou s satellite-based. A major aspect of a communication channel is its capacity or the rate at which it can transfer information. The capacities of different communication channels can vary greatly and are not directly related to the physical medium. A coaxial cable, for example, can have as high a capacity as a satellite channel. Networks can convey information at a wide range of speeds, ranging from a few thousand bits per second for sending a brief text message, to tens of millions of bits per second for sending video images.

Bluetooth is an industrial specification for wireless personal area networks (PANs). Bluetooth provides a way to connect and exchange information between devices such as mobile phones, laptops, PCs, printers, digital cameras, and video game consoles over a secure, globally unlicensed short-range radio frequency. Bluetooth is a radio standard and communications protocol primarily designed for low power consumption, with a short range (power-class-dependent:1 metre, 10 metres, 100 metres) based on low-cost transceiver microchips in each device. Bluetooth lets these devices communicate with each other when they are in range. The devices use a radio communications system, so they do not have to be in line of sight of each other, and can even be in other rooms, as long as the received transmission is powerful enough.

List of applications

More prevalent applications of Bluetooth include:

• Wireless control of and communication between a cell phone and a hands-free headset or car kit. This was one of the earliest applications to become popular.
• Wireless networking between PCs in a confined space and where little bandwidth is required.
• Wireless communications with PC input and output devices, the most common being the mouse, keyboard and printer.
• Transfer of files between devices with OBEX (OBject EXchange).
• Transfer of contact details, calendar appointments, and reminders between devices with OBEX.
• Replacement of traditional wired serial communications in test equipment, GPS receivers, medical equipment and traffic control devices.
• For controls where infrared was traditionally used programs that are required to get additional information about remote devices.
• Sending small advertisements from Bluetooth enabled advertising hoardings to other, discoverable, Bluetooth devices.

Bluetooth vs. Wi-Fi in Networking Bluetooth and Wi-Fi (Wireless Fidelity) both have their places in today's offices, homes, and on the move: setting up networks, printing, or transferring presentations and files from PDAs (Personal Digital Assistant) to computers. Bluetooth is implemented in a variety of new products such as phones, printers, modems, and headsets. Bluetooth is acceptable for situations when two or more devices are in proximity to each other and don't require high bandwidth. Bluetooth is most commonly used with phones and hand-held computing devices, either using a Bluetooth headset or transferring files from phones/PDAs to computers.

Bluetooth also simplified the discovery and setup of services. Wi-Fi is more analogous to the traditional Ethernet network and requires configuration to set up shared resources, transmit files, set up audio links (for example, headsets and hands-free devices), whereas Bluetooth devices advertise all services they actually provide; this makes the utility of the service that much more accessible, without the need to worry about network addresses, permissions and all the other considerations that go with typical networks.

Wi-Fi Wi-Fi uses the same radio frequencies as Bluetooth, but with higher power output resulting in a stronger connection. Wi-Fi is sometimes, but rarely, called "wireless Ethernet." Although this description is inaccurate, it provides an indication of Wi-Fi's relative strengths and weaknesses. Wi-Fi requires more setup, but is better suited for operating full-scale networks because it enables a faster connection, better range from the base station, and better security than Bluetooth. One method for comparing the efficiency of wireless transmission protocols such as Bluetooth and Wi-Fi is spatial capacity, or bits per second per square meter.

Computer Requirements A personal computer must have a Bluetooth dongle in order to be able to communicate with other Bluetooth devices (such as mobile phones, mice and keyboards). While some portable computers and fewer desktop computers already contain an internal Bluetooth dongle, most computers require an external USB Bluetooth dongle. Unlike its predecessor, iRDA, in which each device requires a separate dongle, multiple Bluetooth devices can communicate with a computer over a single dongle.

The term bandwidth refers to the amount of data that is transmitted over the network per unit oftime, typically expressed as bits per second.

Bandwidth is related to the needs of the communication application. For ex­ample, typing characters on a keyboard is limited by the typing speed of the user, so only a small bandwidth is needed for such an application. In an application such as linking a personal computer to a time-sharing computer service, data are typically transmitted at 1200 to 9600 bits per second.

Traffic over a communication channel is rarely smooth and continuous. Just as freeways are jammed during rush hour and empty late at night, or electrical con­sumption rises dramatically on a hot evening when air conditioners and appli­ances are turned on, communication channels also have peaks and valleys. Similarly, adding more lanes to already-crowded freeways does not necessarily solve the traffic problem, and adding more capacity to a communication chan­nel does not necessarily provide better communication capability. Other solutions involve more effective utilization of the bandwidth that is already there.

Compression (and decompression) is a technique for shrinking huge data files for storage and transmission. In our highway analogy, compression is the equivalent of carpooling. By packing more data into each packet, the capacity of an existing channel can be used more effectively.

A multiplexer is a device that allows multiple communication signals to share one communication channel. This low­ers communication costs by allowing more efficient use of a channel.

Frequency-division multiplexing in­volves dividing the transmission channel into different frequencies. Data from each user are then sent over a specific frequency. Radio is a familiar analogy. You can switch among radio stations and listen to each one without interference because each radio station is broadcast­ing at a different frequency. A typical telephone coaxial cable is capable of car­rying 10,000 simultaneous voice conver­sations simply by frequency-division multiplexing the signals that represent individual conversations.

Time-division multiplexing involves dividing the channel on the basis of fixed time intervals called time slots. For ex­ample, many digital channels are di­vided into 24 time slots less than a mil­lionth of a second long, which repeat in cycles of 24. Thus, each user’s data are separated in time from all other users’ data. By assigning a user time-slot num­ber 12, for example, that user’s data will always occupy time-slot number 12.

2.3 Translate the following phrases so that you could form compound nouns.

Kанал зв‘язку, мікрохвильові системи, ретрансляторна антенна, засіб зв‘язку, супутник зв‘язку, наземна станція, супутниковий канал, схема ущільнення, канал передачі, інтервал часу, ретрансляторні станції, можливості зв‘язку.

2.4 Give English equivalents of the following phrases.

Споживання електроенергії, численні сигнали зв‘язку, на основі фіксованих інтервалів часу, цифрові канали, ефективне використання смуги частот, для зберігання і передавання, без завад, пристрій дистанційного контролю, передавати і одержувати інформацію, посилати і одержувати повідомлення, підсилювати сигнал, використовувати світло замість електрики, бути безпосередньо з‘єднаними з фізичним середовищем.

2.5 Find synonyms.

Differ, require, locate, restrict, method, vary, need, shrink, share, connect, link, transmit, situate, exact, involve, replace, convey, sharp, include, substitute, transfer, needs, compress, common, requirements, divide, widespread, send, limit, technique

2.6 Fill in the blanks with the words from the text.

1. Networks can be connected together by either _____________ lines or ___________ canals.

2. Modern telecommunications use ___________ cables because data can be transmitted at a very high speed through extremely wide bandwidth of glass fibres.

3. A technique for shrinking huge data files for storage and transmission is called __________.

4. __________ cables require little physical space, they avoid electromagnetic interference and they are safe because they do not carry electricity.

5. A device that allow multiple communication signals to share one communication channel is called a ______________.

6. ______________ involves dividing the transmission channel into different frequencies.

7. ______________ involves dividing the transmission channel into time slots.

8. Frequency is measured in ____________.

2.7 Explain the following terms in your own words.

Compression, bandwidth, communication channel, multiplexing

2.8 Answer the questions.

1. What physical medium is used by all communication channels?

2. In what units is frequency measured?

3. What types of wire are commonly used to implement communication channel?

4. What are the advantages of fibre-optic cable in comparison with twisted-pair wire and coaxial cable?

5. What are the main categories of communication channels?

6. What types of waves does communication channel use?

7. What type of waves is the most common wireless communication medium? Why?

8. Are the capacities of different communication channels directly related to the physical medium?

9. What is the compression necessary for?

10. How does a multiplexer function?

3.1 Read and translate the following word-combinations.

A hardware component, vice versa, with the advent, in conjunction with, built-in telephone, digitize the image, to convert the signals, a telephone-jack connection, terminate the connection, reliable and convenient to use, facsimile transmission.

3.2 Learn key words and word-combinations.

acoustic modem – акустичний модем

acoustic coupler – гніздо для під’єднання телефону

analog telephone line – аналогова телефонна лінія

digital signal – цифровий сигнал

digitize(v) – перетворювати у цифрову форму

facsimile(n) – факсиміле; точна копія

provide feedback – забезпечувати зворотній зв‘язок

RF(radio-frequency) modem – радіочастотний модем

resolution(n) – роздільна здатність

telephone-jack connections – сполучення через телефонне гніздо

terminate connection – закінчувати зв‘язок

3.3 Read and translate the text.

Modems. The most common piece of data com­munication hardware in use today is the modem (short for modulator demodu­lator). It is popular because the most convenient communication channel is the analog telephone line. A modem at each end of the channel performs the function of converting digital signals into analog signals and vice versa.

Several types of modems are com­monly used. The earliest form is the acoustic modem. It consists of an acous­tic coupler designed to hold the handset of an ordinary telephone as well as mo­dem circuits to convert the signals and to interface with a terminal or personal computer. With the advent of the stan­dard telephone-jack connection, newer modems have taken on a slightly differ­ent form. They consist of the interface circuits along with a standard plug into which the telephone jack fits. These newer modems are typically more reli­able and convenient to use. Specialized modems designed for much higher transmission rates (up to 19,200 bits per second) are used in conjunction with communication channels that support the higher speeds. In wireless metro­politan-area networks, radio-frequency (RF) modems perform the same func­tions as their wired counterparts.

Facsimile or FAX is a method for elec­tronically copying and transmitting an image. FAX machines send and receive images over telephone lines. They scan documents, digitize the image, and transmit the information to another FAX machine, which reconstructs the image and prints it.

Using a FAX machine is similar to making a telephone call. To send a FAX, you first use the FAX’s built-in telephone to dial the number of another FAX ma­chine. After a connection is established, you insert your document into the FAX machine. When the transmission is suc­cessfully completed, the FAX machine provides feedback and terminates the connection. Receiving a FAX is automatic. The FAX machine must, of course, be turned on and connected to a phone line. An incoming call triggers the FAX to begin receiving the document. This type of point-to-point communication re­quires the sending and receiving FAX machines to be connected simulta­neously.

To make sure that FAX machines from different manufacturers can com­municate with one another, all vendors have adopted standard protocols from the Consultative Committee for Interna­tional Telephony and Telegraphy (CCITT). FAX machines can be combined with other computer and communica­tion technologies. FAX boards that con­tain a built-in modem and plug into one of the expansion slots inside of a personal computer enable facsimile trans­mission of word-processing documents without first making a paper copy. By using communication software, the document can be sent to a FAX machine or a comparably equipped computer.

For two devices to communicate, they must “speak the same language. “ What is communicated, and how and when it is communicated must conform to some mutually agreed-upon conventions. A protocol is a formal set of rules for specifying the format and relationship when exchanging data among commu­nicating devices.

Because communication between dissimilar devices is extremely complex, it is desirable to standardize protocols so that any device can use them. Two sys­tems, no matter how different, can com­municate if they use standard protocols. Also, a set of protocols instead of a single protocol is usually needed. These proto­cols are arranged in a hierarchy of layers. The top layers provide services in sup­port of the applications; the bottom layers are concerned with transmitting infor­mation between communicating devices.

By treating each layer independently, it becomes possible to change a protocol at one layer without affecting the other layers. For example, as higher-speed communication technology emerges, only the lower-level protocols need to change. The application can continue to function without having to “know” the details of the physical communication channel.

3.4 Answer the questions.

1. What is the idea behind the modem?

2. How is the modem connected to a telephone line?

3. How does a fax machine operate?

4. What is the protocol used for?

Read and translate the text.

THE INTERNET

The Internet is a computer network made up of thousands of networks worldwide. No one knows exactly how many computers are connected to the Internet. It is certain, however, that these number in the millions. No one is in charge of the Internet. There are organizations which develop technical aspects of this network and set standards for creating applications on it, but no governing body is in control. The Internet backbone, through which Internet traffic flows, is owned by private companies. All computers on the Internet communicate with one another using the Transmission Control Protocol/Internet Protocol suite, abbreviated to TCP/IP. Computers on the Internet use a client/server architecture. This means that the remote server machine provides files and services to the user's local client machine. Software can be installed on a client computer to take advantage of the latest access technology. An Internet user has access to a wide variety of services: electronic mail, file transfer, vast information resources, interest group membership, interactive collaboration, multimedia displays, real-time broadcasting, shopping opportunities, breaking news, and much more. The Internet consists primarily of a variety of access protocols. Many of these protocols feature programs that allow users to search for and retrieve material made available by the protocol.

COMPONENTS OF THE INTERNET The World Wide Web (abbreviated as the Web or WWW) is a system of Internet servers that supports hypertext to access several Internet protocols on a single interface. Almost every protocol type available on the Internet is accessible on the Web. This includes e-mail, FTP, Telnet, and Usenet News. In addition to these, the World Wide Web has its own protocol: HyperText Transfer Protocol, or HTTP. These protocols will be explained later in this document.

The World Wide Web provides a single interface for accessing all these protocols. This creates a convenient and user-friendly environment. It is no longer necessary to be conversant in these protocols within separate, command-level environments. The Web gathers together these protocols into a single system. Because of this feature, and because of the Web's ability to work with multimedia and advanced programming languages, the Web is the fastest-growing component of the Internet.

The operation of the Web relies primarily on hypertext as its means of information retrieval. HyperText is a document containing words that connect to other documents. These words are called links and are selectable by user.A single hypertext document can contain links to many documents. In the context of the Web, words or graphics may serve as links to other documents, images, video and sound. Links may or may not follow a logical path, as each connection is programmed by the creator of the source document. Overall, the Web contains a complex virtual web connections among a vast number of documents, graphics, videos, and sounds.

Producing hypertext for the Web is accomplished by creating documents with a language called HyperText Markup Language, or HTML. With HTML, tags are placed within the text to accomplish document formatting, visual features such as font size, italics and bold, and the creation of hypertext links. Graphics and multimedia may also be incorporated into an HTML document. HTML is an evolving language, with new tags being added as each upgrade of the language is developed and released. The World Wide Web Consortium (W3C), led by Web founder Tim Berners-Lee, coordinates the efforts of standardizing HTML. The W3C now calls the language XHTML and considers it to be an application of the XML language standard.

The World Wide Web consists of files, called pages or home pages, containing links to documents and resources throughout the Internet. The Web provides a vast array of experiences including multimedia presentations, real-time collaboration, interactive pages, radio and television broadcasts, and the automatic "push" of information to a client computer. Programming languages such as Java, JavaScript, Visual Basic, Cold Fusion and XML are extending the capabilities of the Web. A growing amount of information on the Web is served dynamically from content stored in databases. The Web is therefore not a fixed entity, but one that is in a constant state of development and flux.

E-MAIL Electronic mail, or e-mail, allows computer users locally and worldwide to exchange messages. Each user of e-mail has a mailbox address to which messages are sent. Messages sent through e-mail can arrive within a matter of seconds. A powerful aspect of e-mail is the option to send electronic files to a person's e-mail address. Non-ASCII files, known as binary files, may be attached to e-mail messages. These files are referred to as MIME attachments. MIME stands for Multimedia Internet Mail Extension, and was developed to help e-mail software handle a variety of file types. For example, a document created in Microsoft Word can be attached to an e-mail message and retrieved by the recipient with the appropriate e-mail program. Many e-mail programs, including Eudora, Netscape Messenger, and Microsoft Outlook, offer the ability to read files written in HTML, which is itself a MIME type.

TELNET Telnet is a program that allows you to log into computers on the Internet and use online databases, library catalogs, chat services, and more. There are no graphics in Telnet sessions, just text. To Telnet to a computer, you must know its address. This can consist of words (locis.loc.gov) or numbers (140.147.254.3). Some services require you to connect to a specific port on the remote computer. In this.case, type the port number after the Internet address. Example: telnet nri.reston.va.us 185. Telnet is available on the World Wide Web. Probably the most common Web-based resources available through Telnet have been library catalogs, though most catalogs have since migrated to the Web. A link to a Telnet resource may look like any other link, but it will launch a Telnet session to make the connection. A Telnet program must be installed on your local computer and configured to your Web browser in order to work. With the increasing popularity of the Web, Telnet has become less frequently used as a means of access to information on the Internet.

FTP FTP stands for File Transfer Protocol. This is both a program and the method used to transfer files between computers. Anonymous FTP is an option that allows users to transfer files from thousands of host computers on the Internet to their personal computer account. FTP sites contain books, articles, software, games, images, sounds, multimedia, course work, data sets, and more. If your computer is directly connected to the Internet via an Ethernet cable, you can use one of several PC software programs, such as WS FTP for Windows, to conduct a file transfer. FTP transfers can be performed on the World Wide Web without the need for special software. In this case, the Web browser will suffice. Whenever you download software from a Web site to your local machine, you are using FTP. You can also retrieve FTP files via search engines such as FtpFind, located at http://www.ftpfind.com/. This option is easiest because you do not need to know FTP program commands.

E-MAIL DISCUSSION GROUPS One of the benefits of the Internet is the opportunity it offers to people worldwide to communicate via e-mail. The Internet is home to a large community of individuals who carry out active discussions organized around topic-oriented forums distributed by e-mail. These are administered by software programs. Probably the most common program is the listserv. A great variety of topics are covered by listserves, many of them academic in nature. When you subscribe to a listserv, messages from other subscribers are automatically sent to your electronic mailbox. You subscribe to a listserv by sending an e-mail message to a computer program called a listserver. Listservers are located on computer networks throughout the world. This program handles subscription information and distributes messages to and from subscribers. You must have a e-mail account to participate in a listserv discussion group. Visit Tile.net at http://tile.net/ to see an example of a site that offers a searchable collection of e-mail discussion groups. Majordomo and Listproc are two other programs that administer e-mail discussion groups. The commands for subscribing to and managing your list memberships are similar to those of listserv.

USENET NEWS Usenet News is a global electronic bulletin board system in which millions of computer users exchange information on a vast range of topics. The major difference between Usenet News and e-mail discussion groups is the fact that Usenet messages are stored on central computers, and users must connect to these computers to read or download the messages posted to these groups. This is distinct from e-mail distribution, in which messages arrive in the electronic mailboxes of each list member. Usenet itself is a set of machines that exchanges messages, or articles, from Usenet discussion forums, called newsgroups. Usenet administrators control their own sites, and decide which (if any) newsgroups to sponsor and which remote newsgroups to allow into the system. There are thousands of Usenet newsgroups in existence. While many are academic in nature, numerous newsgroups are organized around recreational topics. Much serious computer-related work takes place in Usenet discussions. A small number of e-mail discussion groups also exist as Usenet newsgroups. The Usenet newsfeed can be read by a variety of newsreader software programs. For example, the Netscape suite comes with a newsreader program called Messenger. Newsreaders are also available as standalone products.

CHAT & INSTANT MESSENGING

Chat programs allow users on the Internet to communicate with each other by typing in real time. They are sometimes included as a feature of a Web site, where users can log into the "chat room" to exchange comments and information about the topics addressed on the site. Chat may take other, more wide-ranging forms. For example, America Online is well known for sponsoring a number of topical chat rooms. Internet Relay Chat (IRC) is a service through which participants can communicate to each other on hundreds of channels. These channels are usually based on specific topics. While many topics are frivolous, substantive conversations are also taking place. To access IRC, you must use an IRC software program. A variation of chat is the phenomenon of instant messenging. With instant messenging, a user on the Web can contact another user currently logged in and type a conversation. Most famous is America Online's Instant Messenger, ICQ, MSN and Yahoo also offer chat programs.

4.4 Explain the following terms in your own words.

e-mail, electronic mailbox, a video conference, an electronic bulletin board, an electronic, conference

4.5 Which data communication services would you use for each of these requirements?

1. To send a personal message to a friend who is at a different workstation.

2. To send a copy of a paper document, for instance, a scientific article.

3. To access massive databases, containing all kinds of information.

4. To receive shareware and public domain programs from a user (a group).

5. To find out weather forecasts and sports information from television.

a) fax

b) electronic mail

c) teletext

d) local bulletin board

e) commercial online service

4.6 Fill in the blanks with the words from the text.

1. The Internet is the largest global _____________ network connecting millions of users all over the world.

2. Users can ___________ commercial and non-commercial services of the USA, Canada, Australia and many European countries.

3. _____________ is one of the earliest and most popular services provided by the Internet.

4. _____________ is real-time collaboration between people using video, voice and data.

5. Most users access the Internet through ____________ such as CompuServe and Prodigy.

4.7 Put the verb into the correct form.

1. The Internet which was used mainly by researchers, _____________ more popular in business spheres.(become)

2. Prodigy‘s services ________ particularly at shoppers and the needs of children.(aim)

3. Telecommunications __________ for hundreds of different applications.(use)

4. Electronic mail _________ some special hardware.(require)

5. The Internet ________ very rapid growth in traffic.(experience)

4.8 Proverbs for the Internet. Try to guess what proverbs they originated from.

1. Home is where you hang your @.

2. You cannot teach a new mouth old clicks.

3. Too many clicks spoiled the browse.

4. Do not buy more than you can view.

5. The user and his leisure time are soon parted.

6. There is no place like http://www.home.com

7. Give a man a fish and you feed him for a day: teach him how to use the Net and he won‘t bother you for weeks.

4.9 Answer the questions.

1. What are the advantages of electronic mail over the telephone?

2. What problems can be solved with help of computer-based collaborative work?

3. What are the advantages of a video conference over an electronic conference?

4. What is the role of the Internet in modern life?

5. What is the architecture of the Internet?

6. What hardware and software are necessary to access the Internet?

7. What is the transceiver?

8. What are the most popular transceivers?

9. What is the average speed of transmitting information via the Ethernet?

4.10 Make a report on

1. The Internet as the global information space.

2. The Intranet.

3. The Ethernet.

4. The architecture of the Internet and Ethernet.

5. Services provided by the Internet.

6. Protocols.

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