- •Учреждение образования «высший государственный колледж связи» «чтение и перевод технических текстов по специальности ткс»
- •Часть II
- •Unit 3 Time Division Multiplexing
- •21.1 General definition
- •21.2 Digital time division multiplex structure
- •21.2.1 Frame organisation
- •21.2.2 Frame alignment
- •21.2.3 Signalling
- •1 Learn the words & word combinations:
- •4 Answer the questions:
- •21.3 The digital hierarchy levels
- •21.4 The t carrier framing and coding formats
- •The superframe format
- •21.4.2 The extended superframe format
- •21.4.3 Clear channels for data applications
- •1 Learn the words & word combinations:
- •4 Answer the questions:
- •21.5 The cept pcm-30 framing format
- •21.5.1 Frame composition
- •1 Learn the words & word combinations:
- •21.6.2 Error conditions
- •21.7 Coding schemes
- •1 Learn the words & word combinations:
- •4 Answer the questions:
- •Unit 4 (58) Telephones and headsets
- •58.1 Telephones
- •58.2 Telephone speech functions
- •58.3 Telephone transmitters
- •58.3.1 Carbon granule transmitter
- •58.3.2 Rocking armature transmitter
- •58.3.3 Piezoelectric transmitter
- •58.4 Telephone receivers
- •58.4.1 Rocking armature receiver
- •58.4.2 Moving coil receiver
- •1. Learn the words & word combinations:
- •4. Answer the questions:
- •5. Translate in written form point 58.3.1:
- •58.5 Telephone handset design
- •58.6 Telephone transmission performance
- •58.6.1 Sending sensitivity
- •58.6.2 Receive sensitivity
- •58.6.3 Impedance
- •58.6.4 D.C. Characteristics
- •1 Learn the words & word combinations:
- •3 Find English equivalents:
- •Answer the questions:
- •5 Translate in written form points 58.6.1 – 58.6.4:
- •58.7 Signalling
- •Incoming ringing signals
- •Outgoing 48raveling
- •Dial pulse or loop disconnect 49raveling
- •Dual tone multifrequency 50raveling
- •Loudspeaking telephones
- •1 Learn the words & word combinations:
- •4 Answer the questions:
- •5 Translate in written form points 58.9:
- •58.9 Digital telephones
- •58.10 Telephone standards
- •58.11 Headsets
- •58.12 Headset aesthetics
- •58.13 Headset technical considerations
- •58.13.1 Microphones
- •58.13.2 Earphones
- •58.14 The growing need for headsets
- •58.15 Headset approval process
- •58.16 Headset design criteria
- •1 Learn the words & word combinations:
- •Unit 5 (60) Facsimile transmission
- •60.2 Facsimile types
- •60.2.1 Photofax equipment
- •60.2.2 Weatherfax equipment
- •60.2.3 Pagefax equipment
- •60.2.4 Mobile equipment
- •60.2.5 Government and military equipment
- •60.2.5.1 Strategic requirements
- •60.2.5.2 Tactical requirements
- •60.3 Ccitt document facsimile equipment
- •1 Learn the words & word combinations:
- •3 Find English equivalents:
- •4 Answer the questions:
- •5. Translate in written form points 60.3.4:
- •60.4 G3 facsimile equipment
- •60.4.1 Scanner
- •60.4.2 Data compression
- •60.4.2.1 Modified Huffman
- •60.4.2.2 Modified read
- •60.4.3 Modulation and demodulation
- •60.4.3.1 G3 signal transmission
- •60.4.3.2 Modem operation
- •60.4.3.3 14.4Kbills option
- •1 Learn the words & word combinations:
- •2 Find Russian equivalents; mind the meaning of these expressions:
- •60.4.4.1 Ecm receiver operation
- •60.4.4.2 Ecm performance
- •60.4.5 Printer
- •60.4.6 G3 handshake protocol
- •60.5 64Kbit/s facsimile equipment
- •60.5.1 G4 equipment
- •60.5.2 64Kbit/s g3 type equipment
- •1 Learn the words & word combinations:
- •2 Find Russian equivalents; mind the meaning of these expressions:
- •3 Answer the questions:
- •5. Translate in written form points
- •60.6 G3 networks, switches, gateways and pc fax.
- •60.6.1 Managed network use
- •60.6.2 Facsimile switches
- •60.6.3 Facsimile gateways
- •60.6.4 Pc fax cards
- •60.7 Facsimile futures
- •1 Write out all the words unknown to you, learn them properly.
- •2 Translate in written form points 60.6 – 60.7
- •«Чтение и перевод технических текстов по специальности ткс»
- •Часть II
Учреждение образования «высший государственный колледж связи» «чтение и перевод технических текстов по специальности ткс»
Методическое пособие
по дисциплине «АНГЛИЙСКИЙ ЯЗЫК»
Часть II
для студентов уровня ВО, 3 курс, 5 семестр
специальности 1-45 01 03 – Сети телекоммуникаций
Минск 2005
|
Составитель |
И.Н. Ращинская |
В методическую разработку вошли 5 текстов из оригинального учебника для специальности «Сети телекоммуникаций»:
Antennas
Frequency Division Multiplexing
Time Division Multiplexing
Telephones & Headsets
Facsimile transmission
Рецензент |
Е.М. Игнатьева |
Издание утверждено на заседании кафедры ГН
«__» ______ 2004г., протокол № __
Зав.кафедрой ____________Л.П. Томилина
Содержание
Unit 3 (21)Time Division Multiplexing |
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Part 1 |
4 |
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Part 2 |
11 |
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Part 3 |
20 |
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Part 4 |
24 |
UNIT 4 (58) Telephones and headsets |
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Part 1 |
31 |
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Part 2 |
38 |
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Part 3 |
48 |
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Part 4 |
55 |
UNIT 5 (60) Facsimile transmission |
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Part 1 |
63 |
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Part 2 |
72 |
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Part 3 |
79 |
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Part 4 |
87 |
Unit 3 Time Division Multiplexing
PART 1 (21.1 – 21.2)
21.1 General definition
In telephone systems a time division multiplexer, better known as a TDM, is generally defined as a device that distributes a number of channels periodically in time through the intermediary of pulse modulation. Each pulse corresponds to a channel and is interleaved between those of other channels. Hence, a time division multiplexed signal is always composed by means of synchronous sampling of the channels, with pulses shifted with respect to each other. This is illustrated in Figure 21.1. The interleaved channels form one frame of a duration corresponding to the sampling period Ts. The pulse modulation used can be analog (e.g. РАМ, PPM) or digital (PCM).
With rime division multiplexing time is a relative value, i.e. TDM requires a reference point in the frame cycle to which the receiver must be synchronised in order to correctly demultiplex the stream of pulses it receives and extract the signals concerning each channel individually. Since the receiver must be continuously synchronised in both frequency and phase this reference point is repeated periodically. The easiest way to understand this is to cyclically represent the time division multiplexing process as illustrated in Figure 21.2.
Figure 21.2 depicts a rotating switch S scanning a number of channels connected to its inputs. The channels are scanned one by one in the order they are encountered by the switch: channel 1 is sampled at time tj, channel 2 at time Xy and finally channel n at time t , after which the process is repeated. The resulting output signal is composed of the samples of the different channels, shifted over a time period given by Equation 21.1.
(21.1)
If the channels presented at the input are pulse amplitude modulated signals, we obtain a signal as depicted in Figure 21.1. At the other side of the connection we find an identical switch executing the opposite operation, i.e. scanning the composite input signal at exactly the same frequency and phase, it demultiplexes the input signal and distributes the extracted signals over the respective channels. Both systems synchronise each time they pass the reference point.
Time division multiplexing has become very important, not only in transmission but also in switching, particularly in connection to the digital systems.
In the early days of electrical communications a medium such as copper wire carried a single information channel. For economic reasons, in terms of both cost and equipment, it was necessary to find ways of packing multiple channels onto one physical link. The resulting system is referred to as a carrier. Digital signals are now transmitted from one location to another by transmission facilities or systems using a multitude of media (paired cable, coaxial cable, analog or digital radio systems, optical fibres, satellite communication).
The synchronous time division multiplexers typically are used as termination equipment of such carrier systems. These multiplexers are better known as Tl or El multiplexers, depending on the multiplexing scheme they use. Tl is generally used in America and is based on the PCM system that was originally designed by AT&T. The name Tl was derived from the identification number of the committee set up by the American National Standards Institute (ANSI). Europe, on the other hand, uses the El system, which is based on CEPT (Conference of Post and Telecommunications) recommendations. The delay with which CEPT has undertaken the definition of a primary digital PCM system has allowed it to profit from the experience of the American systems.
On the international level, the two types of system coexist although they are incompatible, and are a subject of two recommendations of the CCITT. Although both systems will be discussed later in this chapter, Table 21.1 compares their main characteristics. The meaning of the different items will become clear throughout the rest of this chapter.
Before discussing the Tl and El technologies in detail, consider first the general structure of a digital time division multiplex.