Comprehension Check

2.4 Make up no less than 10 questions.

2.5 Read the following text and write a summary to it (no less than 7 sentences) in Russian and English.

Text 2 Telephone

In a conventional telephone system, the caller is connected to the person he wants to talk to by the switches at various exchanges. The switches form an electrical connection between the two users and the setting of these switches is determined electronically when the caller dials the number based upon either pulses or tones made by the caller's telephone. Once the connection is made, the caller's voice is transformed to an electrical signal using a small microphone in the telephone's receiver. This electrical signal is then sent through various switches in the network to the user at the other end where it transformed back into sound waves by a speaker for that person to hear. This person also has a separate electrical connection between him and the caller, which allows him to talk back.

Today, the fixed-line telephone systems in most residential homes are analogue — that is the speaker's voice directly determines the amplitude of the signal's voltage. However although short-distance calls may be handled from end-to-end as analogue signals, increasingly telephone service providers are transparently converting signals to digital before converting them back to analogue for reception. The advantage being that digitized voice data can travel side-by-side with data from the Internet and those digital signals can be perfectly reproduced in long distance communication as opposed to analogue signals, which are inevitably impacted by noise.

Mobile phones have had a significant impact on telephone networks. Mobile phone subscriptions now outnumber fixed-line subscriptions in many markets. There have also been dramatic changes in telephone communication behind the scenes. Starting with the operation of TAT -8 in 1988, the 1990s saw the widespread adoption of systems based upon optic fibers. The benefit of communicating with optic fibers is that they offer a drastic increase in data capacity. TAT-8 itself was able to carry 10 times as many telephone calls as the last copper cable laid at that time and today's optic fiber cables are able to carry 25 times as many telephone calls as TAT-8. This drastic increase in data capacity is due to several factors. First, optic fibers are physically much smaller than competing technologies. Second, they do not suffer from crosstalk, which means several hundred of them can be easily bundled together in a single cable. Lastly, improvements in multiplexing have led to an exponential growth in the data capacity of a single fiber.

Assisting communication across these networks is a protocol known as Asynchronous Transfer Mode (ATM) that allows the side-by-side data transmission mentioned in the first paragraph. The importance of the ATM protocol is chiefly in its notion of establishing pathways for data through the network and associating a traffic contract with these pathways. The traffic contract is essentially an agreement between the client and the network about how the network is to handle the data, if the network cannot meet the conditions of the traffic contract it does not accept the connection. This is important, because telephone calls can negotiate a contract to guarantee themselves a constant bit rate, something that will ensure a caller's voice is not delayed in parts or cut-off completely. There are competitors to ATM, such as Multiprotocol Label Switching (MPLS) that perform a similar task and are expected to supplant ATM in the future. However, this has not yet happened.

Unit 3 Video

3.1 Read and translate the text. Use a dictionary to help you.

Date: 2016-03-03; view: 915