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Text 1. Asynchronous Transfer Mode (ATM)

Broadband integrated services digital network (B-ISDN) is conceived as a digital network envisioned to facilitate worldwide information exchange between any two subscribers without limitations that can be imposed by the communication medium or the media. At least conceptually, B-ISDNs will not only support all types of networking applications that we know of today but also provide the framework to support future applications.

B-ISDN standards are being developed in a number of national standards bodies around the world and by the International Telecommunications Union- Telecommunications Standards Sector (ITU-TS). Another major contributor to solving interoperability problems among asynchronous transfer mode (ATM) equipment is the ATM Forum, а consortium of more than 500 companies worldwide.

Its main mission is to speed up the development and deployment of ATM products through interoperability specifications. The B-ISDN standards and protocol layers are being developed around the BISDN protocol reference model. ATM is the transport mode of choice for B-ISDN. It is a connection-oriented packet-switching technique that uses 53-byte fixed size cells to transfer information in the network. The short packet size of ATM, at high transmission rates, is expected to offer full bandwidth flexibility, provide the basic framework to support a wide range of services required by different applications, and achieve high-resource utilization through statistical multiplexing. With statistical multiplexing, the sum of maximum bit rates of connections multiplexed on a link may exceed the link transmission rate if their average bit rates are (much) less than their maximum. The term asynchronous states that the cells generated by a source may appear at irregular intervals in the network. The connection-oriented nature of ATM arises out of the need to reserve resources in the network to meet the quality of service requirements of applications.

The transfer mode is defined as a technique used for transmission, multiplexing, and switching aspects of communication networks. ATM is envisioned to have the following properties:

- supports all existing services and those with yet unknown characteristics that would emerge in the future in an integrated manner, including voice, video, image, audio, and data;

- minimizes switching complexity;

- minimizes the processing time at intermediate nodes to support very high transmission speeds;

- minimizes the number of buffers required at the intermediate nodes to bound the delay and minimize buffer management complexity.

An ATM cell consists of a 5-byte cell header and a 48-byte payload. The cell header includes the following fields: generic flow control, virtual path identifier, virtual channel identifier, payload type (PT), cell loss priority, and header error control. ATM requires connections to be established prior to data flow. It uses routing tables at each node along the path of a connection that maps the connection identifiers from the incoming links to the outgoing links.



(By Ralf O. Onvural)

Vocabulary

8.2 Compile the vocabulary (term) log as shown in the preface (part of speech, definition, translation, synonyms and antonyms if possible, example of use). Words (concepts) are given below:

Path; broadband; flexibility; multiplexing; node; interoperability; framework; asynchronous; bandwidth; packet switching; cell header; fixed size cells.

 

8.3 Find in the text and suggest English equivalents for the following:

Поле данных (48 байт); организация буферизации данных; идентификатор виртуального канала; на высоких скоростях передачи (данных); быть навязанным; широкий спектр услуг.

 

Grammar

 

8.4 В тексте встречается конструкция, именуемая “Complex subject”: The short packet size of ATM, at high transmission rates, is expected to offer full bandwidth flexibility.

Повторите грамматический материал и перефразируйте предложения, используя предложенное слово и учитывая тему Complex Subject.

 

1) Somebody has told me that Ann is at home.

(is said) Ann……………at home

2) It is thought that life on our planet was brought by aliens.

(is thought) The life on our planet ……..by aliens.

3) Many people believe that Shakespeare wrote more poems that we know of.

(is believed) Shakespeare………… more poems than we know of.

4) Some people believed that somebody had helped Alison during the test.

(was believed) Alison ………..during the test.

5) People suppose that disasters are an inevitable part of our lives.

(are supposed) Disasters………. an inevitable part of our lives.

6) Some people suppose that this abandoned house was a museum in the past.

(is supposed) This abandoned house ………..a museum in the past.

7) They thought that Andrew committed that crime.

(was thought) Andrew………. that crime.

8) Everyone believes that Chelsea is the most expensive team.

(is believed) Chelsea …………..the most expensive team.

9) Everyone believed that Chelsea was the most expensive team.

(was believed) Chelsea………. the most expensive team.

Comprehension Check

 

8.5 Answer the following questions:

1) Is broadband integrated services digital network conceived as a digital network? Why? 2) What are B-ISDN standards being developed by?

3) What is the ATM-Forum?

4) What is its main mission?

5) What are the B-ISDN standards and protocol layers being developed around?

6) What is an asynchronous transfer mode?

7) How many fixed size cells does this packet switching technique use?

8) What is the short packet size of ATM expected to do?

9) What does the term asynchronous state?

10) Do you know the properties of ATM?

11) What does an ATM cell consist of?

12) What fields does the cell header include?

13) Does ATM require connections to be established prior to data flow?

 

8.6 Read and translate the following terms (word combinations:

Integrated services digital network, to facilitate, a subscriber, communication medium, national standard bodies, interoperability, a reference model, a packet-switching technique, to transfer information, at high-transmission rates, to provide the basic framework, different applications, average, to emerge, at intermediate nodes, the delay, cell header, virtual path identifier, payload, connection, data flow, to map, incoming links, outgoing links.

 

8.7 Find words in the text to which the following are antonyms:

Minor, synchronous, to slow down, narrow, known, to maximize, trailer, regular, outgoing, national, analog.

Developing language skills

8.8 Complete the following sentences:

1) Asynchronous transfer mode is . . . . . . . . . that uses 53-byte fixed size cells to transfer information in the network.

2) . . . . . . . are being developed in a number of national standards bodies around the world.

3) The term asynchronous states that the cells . . . . . . . . may appear at irregular intervals in the network.

4) An ATM cell . . . . . . . a 5-byte cell header and a 48-byte payload.

5) ATM requires connections to be established prior to . . . . . . .

 

8.9 Make the following sentences negative:

1) Each country developed its own cellular system.

2) The network with leased fiber formed a bi-directional, self-healing fiber optic cable system.

3) Nokia supplied GSM switching equipment last month.

4) The network operators made a lot of money from the traffic in August.

5) This cell-based mobile system appeared in 1973.

6) Cell delineation determined the cell boundaries from the received bit stream.

7) A low probability corrupted cell delivery capabilities.

8.10 Read the following text, guess or suggest a title to it, and write a summary (approximately 7 sentences):

Text 2. ________________________

The Internet has benefits but also drawbacks. Because of this, some organizations have developed their own versions called intranets. For example, a school might decide that open access to the Internet is not appropriate for all students, so develops an intranet. What would this intranet look like?

The school has a number of LANs which are connected together to form WAN. Students have access to various parts of the WAN. It includes an email service for teachers and for students. Students often use it for handing in homework which has been done on computer using resources made available on the WAN.

Teachers use the WAN to send messages to students about work and also about clubs and societies. The teacher in charge of the hockey team can send an email to all the players, marked urgent, telling them that the game this evening is cancelled. The science teacher can make information available to students in the form of web pages either taken from the Internet or created especially for the school WAN.

Students can access the WAN at school but also through their Internet connection from their home computer. To do this they will need a user ID and a password. The WAN is now a small version of the Internet - it even has pages of information which look like Internet pages because they are created in the same way.

Access to information on the WAN is via a web browser, just like on the Internet. A network used in this way is called an intranet.

Both intranets and the Internet have a large amount of information and can be used for communication. They both use browser software to allow a user to access information in web pages.

The main difference between an intranet and the Internet is size: an intranet is a small version of the Internet. In order to see and use the contents of an intranet you need to be known to the system and have logon details to identify yourself. The need for users to be known to the system and the consequent restriction on the number of people using it leads to a number of important differences between intranets and the Internet.

Advantages of intranets.

1. Because the membership of the intranet is restricted, the views that are posted there are more likely to be relevant (they will be about school or schoolwork).

2. The information on the intranet will be useful (information on the school intranet will be aimed at IGCSE level of understanding, not university level).

3. The information on the intranet will be reliable (information on the intranet will be correct and there will be no hoax sites).

4. There are fewer people using the intranet and there will be a limited amount of information on it. This will mean that communication and access to the information will be much faster; it will also be much easier to search for the required information.

5. Using the intranet is safer than using the Internet because the intranet does not have any inappropriate material on it and the people who are using it are all from within the school.

6. The intranet is less susceptible to hacking and viruses because access to it is limited.

Disadvantages of intranets.

1. Intranets are restricted so they have the disadvantage of not having the same volume of information as the Internet.

2. Intranets tend only to have one view whereas the Internet will provide different arguments from different people about a topic. (The science department may only have information about the beginning of the universe being due to the big bang because that is what is on the syllabus. There are many other theories about the start of the universe which would be featured on the Internet but not necessarily on the intranet.) Because of the need to control the size of the intranet it is necessary to be very selective about the information on it. This means that the information tends to reflect the views of the people who decide the information to be included, in this case the science teacher.

3. Communication on the intranet is fine as long as the people who you need to communicate with are also members of the organization and hence have access to the intranet. This is very restricting and communication with others outside the organization needs to be done by using the Internet.

 

8.11 Make up 10 questions of your own about the information in text 2.

Unit 9

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

 

Text 1. Echo cancellation

Full-duplex data transmission over a single twisted-pair cable permits the simultaneous flow of information in two directions when the same frequency band is used. Examples of this technique are digital communication systems that operate over the telephone network. In a digital subscriber loop, at each end of the full-duplex link, a circuit known as a hybrid separates the two directions of transmission. To avoid signal reflections at the near- and far-end hybrid, a precise knowledge of the line impedance would be required. Since the line impedance depends on line parameters that, in general, are not exactly known, however, an attenuated and distorted replica of the transmit signal leaks to the receiver input as an echo signal. Data-driven adaptive echo cancellation mitigates the effects of impedance mismatch.

A similar problem is caused by crosstalk in transmission systems over voicegrade unshielded twisted-pair cables for local-area network applications, where multipair cables are used to physically separate the two directions of transmission.

Crosstalk is a statistical phenomenon due to randomly varying differential capacitive and inductive coupling between adjacent two-wire transmission lines. At the rates of several megabits per second that are usually considered for local-area network applications, near-end crosstalk represents the dominant disturbance; hence near-end crosstalk cancellation must be performed to ensure reliable communication.

In voiceband data modems, the model for the echo channel is considerably different from the echo model adopted in baseband transmission. In fact, since the transmitted passband signal is obtained by modulating a complex-valued baseband signal, the far-end echo signal may experience significant jitter and frequency shift, which are caused by signal processing at intermediate points in the telephone network. Therefore, a digital adaptive echo canceller for passband transmission needs to embody algorithms that account for the presence of such additional impairments.

(Giovanni Cherubini. IBM Zurich Research Laboratory)

Vocabulary

9.2 Compile the vocabulary (term) log as shown in the preface (part of speech, definition, translation, synonyms and antonyms if possible, example of use). Words (concepts) are given below:

full-duplex; a digital subscriber loop; a circuit; impedance; echo cancellation; passband; mismatch; disturbance; jitter; crosstalk; algorithm; a hybrid; baseband; impairment.

 

9.3 Find in the text and suggest English equivalents for the following:

На близком (соседнем) конце; зависеть от; дубликат (точная копия); одновременный; неэкранированная витая пара.

Grammar

9.4 Translate the sentences paying attention to Gerund with prepositions:

1) By repeating the experiment you can get additional results. 2) Control unit is used for interpreting the machine instructions. 3) In describing most physical processes one can use mathematical equations. 4) In training specialists practice is as important as theory. 5) In modern computers transistors are used for performing complicated operations. 6) It would be impossible to offer a fully global service without using satellites.

9.5 Translate into Russian paying special attention to Perfect Participle:

1) Having experienced the advantages, we plan to equip our 140 vehicles with mobile communication. 2) Having been repaired, the computer began operating better. 3) Having taken all these factors into account, the latest investment paid for itself. 4) Having repaired the computer, the engineer showed it to the manager. 5) Having been installed, the nonsystem premises wiring began to meet the requirements of an insulation standards. 6) Having said this, she stopped speaking. 7) Having established the channel response, the scheme illustrates noise spectrum identification.

 

Comprehension Check

 

9.6 Translate the following words and word combinations into Russian. Find and write out sentences with them:

Over a single twisted pair cable, the simultaneous flow of information, the same frequency band, at each end, to operate, to separate, signal reflections, precise knowledge, in general, to mitigate the effects, crosstalk, unshielded, due to, at the rates of, the dominant disturbance, cancellation, to ensure reliable communication, to be different from, the transmitted passband signal, frequency shift, jitter, at intermediate points, to account for.

9.7 Find the corresponding ending for the following statements:

1) This sequence is converted into an analog signal…

2) To avoid signal reflections at the near and far-end hybrid,….

3) The signal obtained after echo cancellation…..

4) The transmitted data consist of a sequence of…..

5) Near-end crosstalk cancellation must be performed……

a) a precise knowledge of the line

b) impedance would be required.

c) is processed by a detector.

d) by a digital to analog converter.

e) to ensure reliable communication.

f) independent and identically disturbed

g) real-valued symbols.

 

Developing language skills

9.8 Complete the sentences with the correct preposition:

1) Signalling constitutes the control infrastructure ….. the modern

telecommunication network.

2) The signalling link functions correspond ….. the data link layer.

3) In modern circuit switches, crosspoint memory is frequently found ….. a

common random access memory.

4) Conversion of signals ….. analog to digital may occur in the switch.

5) The line impedance depends ….. line parameters.

6) The telephone uses normal human speech and therefore can be used ….. anyone.

 

9.9 Read the following text, guess or suggest a title to it, choose and insert the proper verb form, and write a summary (approximately 7 sentences):

Offers, operated, interconnects, be carried, called, is connected, occurs, connects, connecting, carried, placed.

Text 2.___________________

The switched network ….. not only telephones but also facsimile machines, cellular telephones, and personal computers – anything that ….. to the network. The telephones and other station apparatus in homes are all connected by pairs of copper wire to a signal point, ….. the protector block, which ….. simple protection to the network from over voltages. A twisted pair of wires then ….. the protector block all the way back to the central office. Many twisted pairs are all ….. together in a cable that can be burried underground, ….. in conduit, or strung between telephone poles.

The twisted pair of wires ….. station apparatus to the central office is called the local loop. The very first stage of switching ….. at the central office. From there, telephone calls may be connected to other central offices, over interoffice trunks.

Calls may also……… over much greater distances by connection to the longdistance networks….. by a number of interchange carriers.

 

9.10 Make up 10 questions of your own using the information in text 2.

 

 

Unit 10

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






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