Tài liệu miễn phí Kĩ thuật Viễn thông
Download Tài liệu học tập miễn phí Kĩ thuật Viễn thông
Mạng và viễn thông P12
Signalling System Noe 7 TheITU-Tsignallingsystemnumber7, SS number7,SS7,CCITT7,C7 or numberseven signalling system is the most recently developed of telephone network signalling systems. It is already widely deployed in digital telephone networks and ISDNs across the world, and also will be a ‘cornerstone’ of ‘intelligent networks’ and broadband ISDNs (B-ISDN).
8/29/2018 6:10:16 PM +00:00
Mạng và viễn thông P13
Synchronous Digital Hierarchy (SDH) and Synchronous Optical Network (SONET) The synchronous hierarchy digital (SDH) is emergingthe as universal technology for transmission telecommunications in networks. the publication Since first of international standards by ITU-T in 1989, SDH equipment has been rapidly developedand deployed across the world,andisrapidlytakingoverfromitspredecessor,thePlesiochronousDigitalHierarchy (PDH).ThischapterdescribesSDHandtheNorthAmericanequivalentofSDH,SONET (SynchronousOpticalNetwork),fromwhichitgrew...
8/29/2018 6:10:16 PM +00:00
Mạng và viễn thông P14
Operator Assistance and Manual Services Early telephone networkswere all manually operated.In the 1950s automatic networks began to take over, but even today they havefailed 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 network and to connect them to the required extension.
8/29/2018 6:10:16 PM +00:00
Mạng và viễn thông P15
Mobile Telephone Networks 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 because they may be deprived also of the opportunity to refer to others for advice or information. For these individuals, the advent of mobile communications promises a era, one in which there will never be excuse for being new an ‘out-of-touch’.
8/29/2018 6:10:16 PM +00:00
Mạng và viễn thông P16
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 network. Much interest, in particular, has been his channelled into radio technologies(so-called‘radio-in-the-localloop’ or ‘wireless localloop’, WLL), as these are seen as aquickandeconomic way to create newaccess infrastructure, bypassing the dependence on the established monopoly operators for ‘last-mile’ connections....
8/29/2018 6:10:16 PM +00:00
Mạng và viễn thông P17
Fibre in the Loop (FITL) and Other Access Networks Theadvent ofopticalfibrecommunicationhascoincidedwithaworldwidetrendtowards deregulation public of telecommunication network services. This caused has rapid heavy investment in optical fibre networks, including access networks for the connection of customers.
8/29/2018 6:10:16 PM +00:00
Mạng và viễn thông P18
Packet Switching Packet switching emerged in the 1970s as an efficient means of data conveyance. It overcame the inability of circuit-switched (telephone) networks to provide efficiently for variable bandwidth connections for bursty-type usage as required between computers, terminals and storagedevices.
8/29/2018 6:10:16 PM +00:00
Mạng và viễn thông P19
Local Area Networks (LANs) We have seen how packet switching has contributed greatly to the efficiency and flexibility of ‘wide area’ data networks, involving a large number of devices spread at geographically diverse locations. Packet switching, however, is not so efficient for smaller scale networks, those limited to linking personal computerswithin an office building; that is the realm of an alternative type of packet-switched-like network called a local area network or LAN for short. In this chapter we discuss the concept of a LAN and the various technical realizations which are available. ...
8/29/2018 6:10:16 PM +00:00
Mạng và viễn thông P20
Frame Relay For datatransfer, X.25-based packet switching has established itself worldwide as a standard and very reliable means. However, X.25 is not a technique suited to the higher quality and speeds of so by modern data communications networks, and it is beginning to be supplanted 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 overcome these problems....
8/29/2018 6:10:16 PM +00:00
Mạng và viễn thông P21
Campus and Metropolitan Area Networks (MANs) Metropolitan area networks (MANs) are network technologies similar in nature to local area networks (LANs), but with the capability to extend the reach of the LAN across whole cities or metropolitan areas, rather than being limited to, say, 100-200 metres of cabling. MANS have evolved because of the desire companies to extend LANs throughout company office buildings of spread across a campus or a number of different locations in a particular city.
8/29/2018 6:10:16 PM +00:00
Mạng và viễn thông P22
Electronic Mail, Znternet and Electronic Message Services The ability to connect two computers together and, with relative ease, to send information from one to the other, is bringing a revolution in the way in which business and life as a whole is conducted. Today it is possible to run your bank account from home, book your holiday, send electronic messages to your work colleagues or friends, and look up to see what is on at the theatre in London orNew York City.Alternatively companies may make their orders to and pay their bills from their suppliersby computer program and‘electronic data interchange’....
8/29/2018 6:10:16 PM +00:00
Mạng và viễn thông P23
The Message Handling System (MHS) The message handling system(MHS) is a concept developed by ITU-T thatis intended to lead to the interconnectivity of all different types of message conveying systems, e.g. telephone, telex, facsimile, electronic mail, etc. MHS sets out a simple model of basic interconnection between systems. As it does so it defines a new dictionary of standard terms and jargon to describe the various phases of a communication.
8/29/2018 6:10:16 PM +00:00
Mạng và viễn thông P24
Mobile and Radio Data Networks Just as computers and datacommunication are revolutionizing office life, so mobile and radio data networks are enabling corporate computer networks be extendedto every part of the comto pany’s business, including the mobile sales force, the haulage fleet and the travelling executive. Data network techniques can now also be usedto trace and pinpoint trucks on the roador ships at sea.
8/29/2018 6:10:16 PM +00:00
Mạng và viễn thông P25
Broadband, Multimedia Networks and the B-ZSDN The emergence of ‘multimedia’ computers and software which use all sorts of different audio, data, image and video signals simultaneously has heralded a new generation of computers and computer ‘applications’ and spurred the need to develop and deploy a new universal technology for telecommunications
8/29/2018 6:10:16 PM +00:00
Mạng và viễn thông P26
Asynchronous Transfer M o d e ( ATM) ATM looks set to become the first universal telecommunication technology, capable of switching and transporting all types of telecommunication connection (e.g. voice,data video, multimedia). It willformthebasisofthefuture broadbandintegratedservicesdigitalnetwork(B-ISDN). Because of the anticipated importance of ATM, wediscussherethetechnicalprinciples and terminology in depth, defining the main jargon and explaining what marks out ATM from its predecessors. In particular, discuss the principlesof statistical multiplexing and the specifics of we cell switching. ...
8/29/2018 6:10:16 PM +00:00
Mạng và viễn thông P27
Telecommunications Management Network (TMN) The goalof the ‘telecommunications management network’o r ‘ T M Nis to provide for consistent and efficient management of complex telecommunications networks. The T M N model describes the basic operating and management functionswhich a network operator has to conduct and the standard interfaces to be used between network components and network managementsystems.
8/29/2018 6:10:16 PM +00:00
Mạng và viễn thông P28
Network Routing, Znterconnection and Znterworking The control of the routing of calls and connections (so-called ‘traffic’) across telecommunications networks is the most difficult but most important responsibility of a network operator. Only by careful planning and management of appropriate call and traffic routing plans can the network operator ensure successful connection of calls and the efficient use of network resources.
8/29/2018 6:10:16 PM +00:00
Mạng và viễn thông P29
Network Numbering and Addressing Plans Thenetworknumbering or addressingplanis an important part ofthenetworkrouting plan, because the network address is the identification used by a caller to identify the customer or network port to which he wishes to be connected. Based on the network address, switched connectionswithinalltypesofnetwork are established.Inthischapterwediscussthefive basicnumbering and addressing schemes, and the principles that goalongwiththem
8/29/2018 6:10:16 PM +00:00
Mạng và viễn thông P30
Teletrafic Theory Telecommunication networks, like roads. are saidcarry ‘traffic’, consisting not of vehicles but of to telephone callsor data messages. The more traffic there is, the more circuits and exchanges must be provided. On a road network the more cars and lorries, the more roads and roundabouts are needed. In any kind of network, if traffic exceeds the design capacity then there will be pockets of congestion.
8/29/2018 6:10:16 PM +00:00
Mạng và viễn thông P31
Trafic Monitoring and Forecasting Having explained the underlying principles of electrical communication and the statistical ‘laws’ oftelecommunicationstraffic, we cannowconsiderthepracticaldesignandoperationof networks. A prime concern is to ensure that there are adequate resources to meet the traffic demand, or to prioritize the use of resources when shortfalls are unavoidable. Two things have to be done to keep abreast of demand.
8/29/2018 6:10:16 PM +00:00
Mạng và viễn thông P32
Network Trafic Control Traffic control is as much art as it is science, and the profits are gratifying. The right control mechanisms and routing algorithms in the right places will determine the overall performance and efficiency of our network. What is more, they will giveus simpler administration, better management and lower costs. This chapter describes a number of these admirable devices: first the simple methodscommonlyusedforoptimizingnetworkroutingundertypical‘normal-dayloading’ conditions; then we look at recent more powerful and complex techniques, together with some of the practical complications facing telecommunications today. ...
8/29/2018 6:10:16 PM +00:00
Mạng và viễn thông P33
Practical Network Transmission Planning Transmissionmedia exist to convey information across networks. No matter what form the information takes (be voice, video,data, or some other form), the prime requirement that the it is information received atthedestinationshouldas closelyaspossiblematch that originally transmitted. The signal should be free from noise, echo, interference and distortion, and should be of sufficient strength (or volume) asto be clearly distinguishable by the receiver. The reliability of the service is also important. ...
8/29/2018 6:10:16 PM +00:00
Mạng và viễn thông P34
Quality o Service (QOS) and f Network Performance ( N P ) The maintenance of good quality for any product or service (i.e. its ‘fitness for purpose’ and its price) isofsupremeimportance to theconsumerandthereforerequiresutmostmanagement attention. However, although it easy enoughto test a tangible product destruction, measureis to ment of the quality of a service is more difficult.
8/29/2018 6:10:16 PM +00:00
Mạng và viễn thông P35
Charging and Accounting for Network Use So far we have concerned ourselves entirely with the technical and operational side of running networks and providing telecommunications services. Network operators, if they wantto stay in business, also need to think about capital and operational costs, and how to recover them from their customers.
8/29/2018 6:10:16 PM +00:00
Mạng và viễn thông P36
Maintaining the Network into the design of a network, and no matter how reliable the individual components are, corrective action will always be required in some form or another, to prevent or make good network and component failures, and maintain overall service standards. However, attitudes towards maintenance and the organization behind it vary widely, ranging from the ‘let it fail then fix it’ school of thought right through to ‘prevent faults at any cost’
8/29/2018 6:10:16 PM +00:00
Mạng và viễn thông P37
Containing Network Overload Network designers like think that their traffic models ideally stable, andthat their forecasts to are of future traffic will never be wrong.In real life, however, such assumptions are unwise, because any one of a number of problems may arise, resulting in network overload, and so congestion. The forecast may underestimate demand; there may be a short period of extraordinarily high pressure (for example at New Year, Christmas, or any public holiday, or following a natural disaster); or there may be a network link switch (exchange) failure. ...
8/29/2018 6:10:16 PM +00:00
Mạng và viễn thông P38
Network Economy Measures People who plan telecommunications networks are always searching for equipment economy a network for a given information carrying capacity; or, measures: reducing cost the of conversely, increasing the information throughput of a fixed network resource. To achieve their aims, can they either maximize electrical the bandwidth available from a given physical transmission path,or (if it is the other kindof economy they want)they can reduce the amount of electrical bandwidth required to carry individual messages or connections. ...
8/29/2018 6:10:16 PM +00:00
Mạng và viễn thông P39
Network Security Measures Improvements in,andexpansionsof,communicationssystemsandnetworkshaveleftmany companies open to breaches in confidentiality, industrial espionage and abuse. Sometimes such breaches go unnoticed for longperiods,andcanhaveseriousbusiness or costimplications. Equally damaging can the impactof simple mistakes, misinterpreted, or distorted information. be Increased belief in the reliability of systems and the accuracy of information has brought great gains in efficiency,but blind belief suppresses the questions which might have confirmed the need for corrections. ...
8/29/2018 6:10:16 PM +00:00
Mạng và viễn thông P40
Technical Standards for Networks In the past, telecommunications networks have been evolved in the minds of their designers to meet well defined but changing user demands. These broadly innovative influences are bound to persist and users can look forward toever more sophisticated telecommunications services in the future. Itwas onlyin themid-1960s that customer-dialled international telephone callsfirst became possible, and in those days such calls were for therich alone.
8/29/2018 6:10:16 PM +00:00
Mạng và viễn thông P41
Building, Extending and Replacing Networks It is rare to come across a telecommunications network that is not in a state of continuous evolution. At its simplest, a network could be expanding simply to cope with increased demand. In addition the network may be expected at the same time to provide increasingly sophisticated telecommunications services.
8/29/2018 6:10:16 PM +00:00