COMMUNICATION NETWORKS

COMMUNICATION NETWORKS

AIM:

To recognize the English technical terms related to communication networks;

OBJECTIVES:

On successfully completing this unit the student should be able to:

identify correctly the terms defining all types of transmission media;

recognise the specific terms related to cable networks, radio waves and communications satellites;

describe the components of communications networks;

identify the types of equipment used for obtaining reliable signal transmission;

describe the operation principle of each type of communication network;

assimilate at least 30 terms specific of signal transmission;

KEY TERMS:

wire, cable, telecommunications services, to connect, telephone switching facility, coaxial cable, video channel, subscriber, head-end, amplifier, process, retransmit, fibre-optic cable, pulsed beams of laser light, pulses of light, 'backbone' link, Internet traffic, antenna, AM and FM radio, beam, dish-shaped antenna, high-capacity link, ionosphere, orbit, geostationary or geosynchronous orbit, Earths rotation, coverage area, relay function, 'bent pipes'.

COMMUNICATION NETWORKS

1. WIRES AND CABLES

Wires and cables were the original medium for telecommunications and are still the primary means for telephone connections. Wire line transmission evolved from telegraph to telephone service and continues to provide the majority of telecommunications services. Wires connect telephones together within a home or business and also connect these telephones to the nearest telephone switching facility.

Other wire line services employ coaxial cable, which is used by cable television to provide hundreds of video channels to subscribers. Much of the content transmitted by the coaxial cable of cable television systems is sent by satellite to a central location known as the head end. Coaxial cables flow from the head end throughout a community and onward to individual residences and, finally, to individual television sets. Because signals weaken as distance from the head end increases, the coaxial cable network includes amplifiers that process and retransmit the television signals.

2. FIBRE OPTICS CABLE

Fibre-optic cables use specially treated glass that can transmit signals in the form of pulsed beams of laser light. Fibre-optic cables carry many times more information than copper wires can, and they can transmit several television channels or thousands of telephone conversations at the same time. Fibre-optic technology has replaced copper wires for most transoceanic routes and in areas where large amounts of data are sent.  This technology uses laser transmitters to send pulses of light via hair-thin strands of specially prepared glass fibres. New improvements promise cables that can transmit millions of telephone calls over a single fibre. Already fibre optic cables provide the high capacity, backbone' links necessary to carry the enormous and growing volume of telecommunications and Internet traffic.

3. RADIO WAVES

Wireless telecommunications use radio waves, sent through space from one antenna to another, as the medium for communication. Radio waves are used for receiving AM and FM radio and for receiving television. Cordless telephones and wireless radio telephone services, such as cellular radio telephones and pagers, also use radio waves. Telephone companies use microwaves to send signals over long distances. Microwaves use higher frequencies than the radio waves used for AM, FM, or cellular telephone transmissions, and they can transmit larger amounts of data more efficiently. Microwaves have characteristics similar to those of visible light waves and transmit pencil-thin beams that can be received using dish-shaped antennas. Such narrow beams can be focused to a particular destination and provide reliable transmissions over short distances on Earth. Even higher and narrower beams provide the high-capacity links to and from satellites. The high frequencies easily penetrate the ionosphere (a layer of Earths atmosphere that blocks low-frequency waves) and provide a high-quality signal.

COMMUNICATIONS SATTELITES

Communications satellites provide a means of transmitting telecommunications all over the globe, without the need for a network of wires and cables. They orbit Earth at a speed that enables them to stay above the same place on Earth at all times. This type of orbit is called geostationary or geosynchronous orbit because the satellites orbital speed operates in synchronicity with Earths rotation. The satellites receive transmissions from Earth and transmit them back to numerous Earth station receivers scattered within the receiving coverage area of the satellite. This relay function makes it possible for satellites to operate as 'bent pipes'that is, wireless transfer stations for point-to-point and point-to-multipoint transmissions. Communications satellites are used by telephone and television companies to transmit signals across great distances. Ship, airplane, and land navigators also receive signals from satellites to determine geographic positions.

	You may want to go back to the key words listed at the beginning of the unit and check that you are familiar with each one. Give their Romanian equivalents (if necessary, you can use the glossary provided at the end of the textbook).

EXERCISES

A. READING

The purpose of the following exercises is to develop reading strategies and reinforce topic related vocabulary, not to check background knowledge.

A.1. Look through the text and answer the following questions:

1. Which is the original medium for telecommunications and the primary means for telephone connections?

2. Which type of cable is used by cable television to provide hundreds of video channels to subscribers?

3. Why is it necessary for the coaxial cable network to include amplifiers that process and retransmit the television signals?

4. What kind of transmission medium is used for cordless telephones and wireless radio telephone services, such as cellular radio telephones and pagers?

5. What is the name of communications satellites that provide a means of transmitting telecommunications all over the globe, without need for a network of wires and cables by orbiting Earth at a speed that enables them to stay above the same place on Earth at all times.

A.2. Re-read the text and decide on the uses, advantages and disadvantages of the types of communication networks listed below:

List 1

1. Coaxial cable networks

2. Fibre-optic cable networks

3. Radio waves

B. VOCABULARY WORK

The purpose of the following exercises is to promote the acquisition of new lexical items by providing collocations, terms followed by prepositions lexical sets and translations of the terms considered relevant to the topic.

B.1. Enter the following terms under the appropriate heading in the table below:

List 2.

wireless transfer stations, microwaves, wireless radio telephone services, laser transmitters, to determine geographic positions, geostationary or geosynchronous orbit, satellites orbital speed, high-quality signal, wire line services, head end, coaxial cable;

Table 1

C. LANGUAGE FOCUS: ABILITY/CAPACITY

The purpose of the following exercises is to develop language awareness in terms of expressing ability/capacity.

C.1. Rephrase the following statements using the /phrases in brackets.

1. Fibre-optic cables use specially treated glass that can transmit signals in the form of pulsed beams of laser light. (HAS THE ABILITY OF)

2. Fibre-optic cables carry many times more information than copper wires can, and they can transmit several television channels or thousands of telephone conversations at the same time. (HAVE THE CAPACITY)

3. New improvements promise cables that can transmit millions of telephone calls over a single fibre. ( ARE ABLE TO)

4. Microwaves use higher frequencies than the radio waves used for AM, FM, or cellular telephone transmissions and they can transmit larger amounts of data more efficiently. (ARE SUITABLE FOR)

D. TRANSLATION

The purpose of this exercise is to develop translating skills.

D.1. Translate the following sentences into English:

1. Satelitii de telecomunicatii asigura mijloacele de transmisie necesare in telecomunicatiile de pe intregul glob, fara a necesita o retea de cabluri.

2. Acest tip de orbita este cunoscuta sub denumirea de orbita geostationara sau geosincrona deoarece viteza de deplasare orbitala a satelitului este sincrona cu viteza miscarii de revolutie a pamantului.

E. SPEAKING

The purpose of these exercises is to develop speaking skills with a focus on describing the four main signal transmission media.

E.2. Role play:

Group A: You are sales manager of a large coaxial cable manufacturing company.

Group B: You are sales manager of a large fibre-optic cable manufacturing company.

Group C: You are sales manager of a large antennae manufacturing company.

Imagine you are in a conference regarding the consolidation of the telecommunications system of Romania and you must convince the contracting party of the advantages of the company you represent.