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Hệ thống viễn thông điện tử, Chương 10
Mạng chuyển mạch gói như chỉ rõ trong hình 2.23, gồm một hệ thống chuyển mạch cấp cao để nối những hệ thống chuyển mạch và một hệ thống tập trung cấp cao từ các trạm đầu cuối tới các hệ thống chuyển mạch. Hệ thống tập trung cấp thấp gồm có một PMX và các trạm đầu cuối. Thiết bị ghép kênh gói phục vụ các trạm đầu cuối loại chung và loại gói. Đó là một thiết bị dùng để tập hợp dữ liệu từ các trạm đầu cuối loại chung ở dạng gói, lưu trữ tạm thời...
8/29/2018 6:21:08 PM +00:00
Hệ thống viễn thông điện tử, Chương 11
phần truyền bản tin (MTP) và các phần cho người sử dụng. Có 3 phần cho người sử dụng: - Cho người sử dụng điện thoại (TUP) - Cho người sử dụng số liệu (DUP) và một bộ phận khác mà trong ngữ cảnh này muốn nói tới phần người sử dụng ISDN (ISUP). Hình 3.21 và 3.22 cho thấy các tầng 1, 2 và 3, là các tầng cấu thành MTP. Các đoạn chỉ dẫn kế tiếp mô tả chức nǎng của từng tầng này theo quan điểm hệ thống. Tầng 1 xác định các đặc tính vật lý,...
8/29/2018 6:21:08 PM +00:00
Quy hoạch động
Trong ngành khoa học máy tính, quy hoạch động là một phương pháp giảm thời gian chạy của các thuật toán thể hiện các tính chất của các bài toán con gối nhau (overlapping subproblem) và cấu trúc con tối ưu (optimal substructure). Nhà toán học Richard Bellman đã phát minh phương pháp quy hoạch động vào năm 1953. Ngành này đã được thành lập như là một chủ đề về kỹ nghệ và phân tích hệ thống đã được tổ chức IEEE thừa nhận....
8/29/2018 6:21:00 PM +00:00
Giáo trình môn học Xử lý tín hiệu số
Xử lý tín hiệu số (Digital Signal Processing - DSP) hay tổng quát hơn, xử lý tín hiệu rời rạc theo thời gian (Discrete-Time Signal Processing - DSP) là một môn cơ sở không thể thiếu được cho nhiều ngành khoa học, kỹ thuật như: điện, điện tử, tự động hóa, điều khiển, viễn thông, tin học, vật lý,...
8/29/2018 6:21:00 PM +00:00
Chuyển đổi lý thuyết P4
Non-blocking Networks The class of strict-sense non-blocking networks is here investigated, that is those networks in which it is always possible to set up a new connection between an idle inlet and an idle outlet independently of the network permutation at the set-up time. As with rearrangeable networks described in Chapter 3, the class of non-blocking networks will be described starting from the basic properties discovered more than thirty years ago (consider the Clos network) and going through all the most recent findings on network non-blocking mainly referred to banyanbased interconnection networks. Section 4.1...
8/29/2018 6:20:59 PM +00:00
Chuyển đổi lý thuyết P5
The ATM Switch Model The B-ISDN envisioned by ITU-T is expected to support a heterogeneous set of narrowband and broadband services by sharing as much as possible the functionalities provided by a unique underlying transport layer based on the ATM characteristics. As already discussed in Section 1.2.1, two distinctive features characterize an ATM network: (i) the user information is transferred through the network in small fixed-size packets, called cells1, each 53 bytes long, divided into a payload (48 bytes) for the user information and a header (5 bytes) for control data; (ii) the transfer mode of user information is connection-oriented, that...
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Chuyển đổi lý thuyết P6
ATM Switching with Minimum-Depth Blocking Networks Architectures and performance of interconnection networks for ATM switching based on the adoption of banyan networks are described in this chapter. The interconnection networks presented now have the common feature of a minimum depth routing network, that is the path(s) from each inlet to every outlet crosses the minimum number of routing stages required to guarantee full accessibility in the interconnection network and to exploit the self-routing property....
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Chuyển đổi lý thuyết P7
ATM Switching with Non-Blocking Single-Queueing Networks A large class of ATM switches is represented by those architectures using a non-blocking interconnection network. In principle a non-blocking interconnection network is a crossbar structure that guarantees absence of switching conflicts (internal conflicts) between cells addressing different switch outlets. Non-blocking multistage interconnection networks based on the self-routing principle, such as sorting–routing networks, are very promising structures capable of running at the speed required by an ATM switch owing to their self-routing property and their VLSI implementation suitability....
8/29/2018 6:20:59 PM +00:00
Chuyển đổi lý thuyết P8
ATM Switching with Non-Blocking Multiple-Queueing Networks We have seen in the previous chapter how a non-blocking switch based on a single queueing strategy (input, output, or shared queueing) can be implemented and what traffic performance can be expected. Here we would like to investigate how two of the three different queueing strategies can be combined in the design of a non-blocking ATM switch. The general structure of a non-blocking switch with size N × M is represented in Figure 8.1. Each input port controller (IPC) and output port controller (OPC) are provided with a FIFO buffer of size B i and...
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Chuyển đổi lý thuyết P9
ATM Switching with Arbitrary-Depth Blocking Networks We have seen in Chapter 6 how an ATM switch can be built using an interconnection network with “minimum” depth, in which all packets cross the minimum number of self-routing stages that guarantees the network full accessibility, so as to reach the addresses switch outlet. It has been shown that queueing, suitable placed inside or outside the interconnection network, allows the traffic performance typical of an ATM switch.
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Thông tin thiết kế mạch P1
THE HISTORY OF TELECOMMUNICATIONS According to UNESCO statistics, in 1997, there were 2.4 billion radio receivers in nearly 200 countries. The figure for television was 1.4 billion receivers. During the same year, it was reported that there were 822 million main telephone lines in use world-wide. The number of host computers on the Internet was estimated to be 16.3 million [1]. In addition to this, the military in every country has its own communication network which is usually much more technically sophisticated than the civilian network. ...
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Thông tin thiết kế mạch P2
AMPLITUDE MODULATED RADIO TRANSMITTER A radio signal can be generated by causing an electromagnetic disturbance and making suitable arrangements for this disturbance to be propagated in free space. The equipment normally used for creating the disturbance is the transmitter, and the transmitter antenna ensures the efficient propagation of the disturbance in free space. To detect the disturbance, one needs to capture some finite portion of the electromagnetic energy and convert it into a form which is meaningful to one of the human senses...
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Thông tin thiết kế mạch P3
THE AMPLITUDE MODULATED RADIO RECEIVER The electromagnetic disturbance created by the transmitter is propagated by the transmitter antenna and travels at the speed of light as described in Chapter 2. It is evident that, if the electromagnetic wave encounters a conductor, a current will be induced in the conductor. How much current is induced will depend on the strength of the electromagnetic field, the size and shape of the conductor and its orientation to the direction of propagation of the wave....
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Thông tin thiết kế mạch P4
FREQUENCY MODULATED RADIO TRANSMITTER In Chapter 2, the amplitude of a high-frequency (carrier) sinusoidal signal was varied in accordance with the waveform of an audio-frequency (modulating) signal to give an amplitude modulated (AM) wave which could be transmitted, received, and demodulated to recover the original audio frequency signal. In frequency modulated (FM) radio, the frequency of the carrier is varied about a fixed value in accordance with the amplitude of the audio frequency.
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Thông tin thiết kế mạch P5
THE FREQUENCY MODULATED RADIO RECEIVER In amplitude modulation, the frequency of the carrier is kept constant while its amplitude is changed in accordance with the amplitude of the modulating signal. In frequency modulation, the amplitude of the carrier is kept constant and its frequency is changed in accordance with the amplitude of the modulating signal. It is evident that, if a circuit could be found which will convert changes in frequency to changes in amplitude, the techniques used for detecting AM can be used for FM as well....
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Thông tin thiết kế mạch P6
THE TELEVISION TRANSMITTER The transmission of video images depends on a scanning device that can break up the image into a grid and measure the brightness of each element of the grid. This information can be sent serially or in parallel to a distant point and used to reproduce the image. It is evident that the smaller the size of the grid element, the better the definition of the image. One of the simplest devices which can measure the brightness of light is the phototube
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Thông tin thiết kế mạch P7
THE TELEVISION RECEIVER In Chapter 6, the coding of video signals in a form suitable for transmission over a telecommunication channel was discussed. In this chapter, the techniques for decoding the signals and their presentation on a cathode ray tube will be examined. The television receiver is almost identical to the AM radio receiver in its use of the superheterodyne principle. There are a few differences in the details of the signal processing due to the greater complexity of the system. Figure 7.l shows a block diagram of a typical television receiver....
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Thông tin thiết kế mạch P8
THE TELEPHONE NETWORK The early history of the telephone system has been outlined in Chapter 1. The growth of the telephone system has been truly phenomenal and forecasts show a continuing growth as new services such as data transfer, facsimile and mobile telephone are added. The telephone differs from the broadcasting system in two basic ways: (1) In broadcasting, a few people who, in theory, have information send it out to the many who are presumed to want the information; it is one-way traffic....
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Thông tin thiết kế mạch P9
SIGNAL PROCESSING IN THE TELEPHONE SYSTEM Until the introduction of the digital telephone, there was virtually no signal processing on the subscriber loop. Indeed, there was no need for it. The majority of subscriber loops were able to transmit voice signals with no particular difficulty and in cases where the lines were longer than usual, line ‘‘loading’’ was used with success. Signal processing has two major aims: (1) To improve the quality of signal transmission over the telephone communication channels....
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Thông tin thiết kế mạch P10
THE FACSIMILE MACHINE Although the facsimile machine was invented in the 1840s, it remained largely a device used in the newspaper industry for the transmission of pictures until the mid1980s. There were several reasons for this; some were technical and the others commercial. The technical problems which held up the development of the fax machine are illustrated in Figure 10.1. For simplicity we use the letter H and assume that scanning is carried out horizontally from the top left side to the right. ...
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Thông tin thiết kế mạch P11
PERSONAL WIRELESS COMMUNICATION SYSTEMS The idea that a person could carry around with him a telephone booth of his own is a very attractive one. However, the technology required to make the telephone booth small and light enough for this to be possible, and furthermore convenient to carry, has been available only in the last 30 years. Mobile radio has been available in North America since the 1930s but they were exclusive in the hands of the police.
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Thông tin thiết kế mạch P12
TELECOMMUNICATION TRANSMISSION MEDIA In this chapter the characteristics of the media in which the transmission of signals takes place will be discussed. It so happens that we humans basically communicate through speech=hearing and by sight. Human hearing is from 20 Hz to 20 kHz and we can see only the portion of radiation spectrum from about 4:3 Â 1014 Hz (infrared; l ¼ 7 Â 10À7 m) to approximately 7:5 Â 1014 Hz (ultraviolet; l ¼ 4 Â 10À7 m). These communication channels occupy only small portions of the detectable frequency spectrum which has no lower boundary but has an upper...
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Tối ưu hóa viễn thông và thích nghi Kỹ thuật Heuristic P1
Optimization Issues in Telecommunications The complexity and size of modern telecommunications networks provide us with many challenges and opportunities. In this book, the challenges that we focus on are those which involve optimization. This simply refers to scenarios in which we are aiming to find something approaching the ‘best’ among many possible candidate solutions to a problem. For example, there are an intractably large number of ways to design the topology of a private data network for a large corporation....
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Tối ưu hóa viễn thông và thích nghi Kỹ thuật Heuristic P2
Evolutionary Methods for the Design of Reliable Networks Alice E. Smith and Berna Dengiz Introduction to the Design Problem The problem of how to design a network so that certain constraints are met and one or more objectives are optimized is relevant in many real world applications in telecommunications (Abuali et al., 1994a; Jan et al., 1993; Koh and Lee, 1995; Walters and Smith, 1995), computer networking (Chopra et al., 1984; Pierre et al., 1995), water systems (Savic and Walters, 1995) and oil and gas lines (Goldberg, 1989). This chapter focuses on design of minimum cost reliable communications networks when a set...
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Tối ưu hóa viễn thông và thích nghi Kỹ thuật Heuristic P3
The efficient design of telecommunication networks has long been a challenging optimization problem. It is made difficult by the conflicting, interdependent requirements necessary to optimize the network’s performance. The goal of the designer is to produce a minimum cost network that allows maximum flow of information (in the form of messages) between multiple source-sink pairs of nodes that simultaneously use the network. An optimum design method must also produce a network topology that efficiently routes these messages within an acceptable amount of time...
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Tối ưu hóa viễn thông và thích nghi Kỹ thuật Heuristic P4
Digital Data Service (DDS) is widely used for providing private high quality digital transport service in the telecommunications industry. The network connections of DSS are permanent and its transmission facilities are dedicated, enabling it to transfer digital data with less interference and greater security than switched service. DSS also proves to be appropriate for linking sites that have applications which require a permanent connection and a demonstrated need for frequent data transfer.
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Tối ưu hóa viễn thông và thích nghi Kỹ thuật Heuristic P5
In line with the rapid growth of telecommunications networks in recent years, there has been a corresponding increase in the level of network complexity. Consequently, it is now generally accepted that advanced computer aided simulation and analysis methods are essential aids to the management of large networks. The 1990s will be recalled as the decade of business process re-engineering
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Tối ưu hóa viễn thông và thích nghi Kỹ thuật Heuristic P6
Telecommunications is a vital and growing area, important not only in its own right, but also for the service it provides to other areas of human endeavour. Moreover, there currently seems to be a demand for an ever-expanding set of telecommunication services of ever-increasing bandwidth. One particular technology that has the potential to provide the huge bandwidths necessary if such broadband services are to be widely adopted, is multiwavelength all-optical transport networks (Mukherjee, 1997)....
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Tối ưu hóa viễn thông và thích nghi Kỹ thuật Heuristic P7
The telecommunications access network is the section of the network that connects the local exchange to the customers. At present most of the access network is composed of low bandwidth copper cable. Electronic communications are becoming an essential feature of life both at home and at work. The increasing use of applications that require larger bandwidths (such as the internet and video on demand) are making the copper infrastructure inadequate. These demands could be met using optical fibre technologies....
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Tối ưu hóa viễn thông và thích nghi Kỹ thuật Heuristic P8
This chapter describes the joint application of two soft computing methods – evolutionary algorithms and fuzzy reasoning – to the problem of adaptive distributed routing control in packet-switched communication networks. In this problem, a collection of geographically distributed routing nodes are required to adaptively route data packets so as to minimise mean network packet delay. Nodes reach routing decisions locally using state measurements which are delayed and necessarily only available at discrete sampling intervals. ...
8/29/2018 6:20:59 PM +00:00