Có 20+ tài liệu thuộc chủ đề "tín hiệu truyền dẫn"
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Indeed these last two phrases are at the heart of the Oxford Dictionary’s definition of the word information. Communication, on the other hand, is defined as ‘the imparting, conveyance or exchange of ideas, knowledge or information’. communication, in the sense of information passed to and fro between human beings, and animals, is an activity that goes back beyond recorded times....
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Introduction to Signal Transmission and the Basic Line Circuit. These allow the conveyance of an electrical current or signal from a transmitter at one end of the wires to the receiver at the other end.. There are two basic methods for information encoding which may be applied by the transmitter and decoded by the receiver. As the name suggests, analogue...
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None of the circuits that we have so far discussed are suitable as they stand for long haul communication. With electrical signals the attenuation (as this type of loss in signal strength is called) is caused by the various electrical properties of the line itself. The attenuation becomes more severe as the line gets longer. On very long haul links...
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Data and the Binary Code System. As a necessary introduction to the concept of ‘digital’ transmission, this chapter is devoted to a description of tha method of representing textual and numeric information which is called the ‘binary code’.. 4.1 THE BINARY CODE. Binary code is a means of representing numbers. A single digit in decimal code may represent any of...
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Digital Transmission and Pulse Code Modulation. Now, in the networks of most countries and with wider world international satellite and submarine networks, digital transmission has no rivals. 5.1 DIGITAL TRANSMISSION. In contrast with analogue networks, digital networks are ideal for the direct carriage of data, because as the name suggests a digital transmission medium carries information in the form of...
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In this chapter we deal with the mechanics of the switching process, describing the sequence of functions necessary to establish connections across a telecommunications network. In addition, we describe in outline some of the better known types of switch technology.. Figure 6.2 shows the new switchpoint. Figure 6.2 The same switch matrix a few moments later. The answer to the...
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It includes the means by which the caller may indicate the desired destination, the means for establishment of the path, and the procedure for subsequent ‘cleardown’. The users of the system in Figure 7.1, A and B, are able to talk at will to one another without fear of interruption. The term ringdown originates from the fact that call clearing...
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The title audio or baseband circuit is given because the frequencies of the electrical signals carried by the circuit are a direct match with those of the audio signal they represent.. Audio circuits may be used to carry any of a wide range of bandwidths, although in general the greater the bandwidth to be carried, the shorter the maximum range...
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squeezing every last drop of ‘power’ out of the computers’ relatively restricted capacity.. Cheap semiconductors heralded the appearance of the microcomputer, which when packaged with the newly developed floppy diskette systems, opened a new era of cheap and widespread com- puting activity. Suddenly, computing was within reach of the masses, and the creation and storage of computer data was easy,...
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to a variety of services while reducing the cost of provision of these services both to the admin-. istration and to the customer. 10.1 THE CONCEPT OF ISDN. Second, that this digital network is not one between exchanges, but it extends to the customers. Figure 10.1 illustrates these principles.. Figure 10.1 ISDN. 10.2 BEARER, SUPPLEMENTARY AND TELESERVICES. The specification of...
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This chapter commences by describing the ‘intelligent networks’ as a concept, and then goes on to give examples of the new services that we can expect from it.. 11.1 THE CONCEPT OF INTELLIGENT NETWORKS. The forerunner was AT&T’s database 800 service, and AT&T continue to be a key driver of the technology. If we were now to examine a second...
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The user parts of the system that have been developed so far are. The MTP and SCCP form the ‘foundations’ of the system, providing for carriage of messages. Initially the SS7 system was designed so that the MTP could be used in association with any or all of the telephone, data and ISDN user parts. However, following the emergence of...
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In particular, the chapter describes the features of SDH which characterize its advantages over PDH.. 13.1 HISTORY OF THE SYNCHRONOUS DIGITAL HIERARCHY (SDH). The fact that SDH is synchronous adds greatly to the efficiency of the transmission network, and makes the network much easier to manage.. 13.2 THE PROBLEMS OF PDH TRANSMISSION. As we also discussed, three distinct PDH hierarchies...
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Operator Assistance and Manual Services. In the 1950s automatic networks began to take over, but even today they have failed to supplant all manual ‘assistance services’. In the public network human operators provide a ‘safety net’ of assistance and advice for customers, and in some private networks human PBX operators are still employed to answer incoming calls from the public...
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Being away from a telephone, a telex or a facsimile machine has become unacceptable for many individuals, not only because they cannot be contacted, but also because they may be deprived of the opportunity to refer to others for advice or information. 15.1 RADIO TELEPHONE SERVICE. The mobile stations were weighty but were nonetheless popular for commercial ‘car telephone’ service,...
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Cordless Telephony and Radio in the Local Loop (RILL). The rapid deregulation of telephone network services taking place during the 1990s has brought a large number of new public network operators to the market, each of which has an interest in optimizing the cost of customer connection to his network. Much interest, in particular, has been channelled into radio technologies...
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Fibre in the Loop (FITL) and Other Access Networks. This has caused rapid heavy investment in optical fibre networks, including access networks for the connection of customers.. This in turn has brought not only focus onto the development of new modulation and multiplexing technologies for use in conjunction with optical fibres themselves, but also the development of new techniques t...
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In this chapter we discuss the basics of packet switching and ITU-T’s X.25 recommendation, nowadays the worldwide technical standard interface to packet-switched networks. 18.1 PACKET SWITCHING BASICS. Figure 18.1 illustrates how a link within a packet switching network is used to carry the jumbled-up packets of various different messages and the use of the information carried in the packet header...
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We have seen how packet switching has contributed greatly to the efficiency and flexibility of. 19.1 THE EMERGENCE OF LANs. LANs emerged in the late 1980s as the most important means of conveying data between different computers and computer peripheral devices (printer, file server, electronic mail server, fax gateway, host gateway, computer printer, scanner, etc.) within a single office, office...
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Frame Relay. However, X.25 is not a technique suited to the higher quality and speeds of modern data communications networks, and so it is beginning to be supplanted by new techniques, among them ‘frame relay’. In this chapter we start by discussing the shortcomings of X.25-based packet switching in carrying highspeed bitrates and explain how frame relay was designed to...