The telephone network

Bài giảng “Telephony - Chapter 2: Subscriber access to the telephone network” giới thiệu sơ đồ khối chức năng của điện thoại tương tự, quay số bằng xung thập phân, quay số bằng DTMF, tín hiệu chuông,… Mời các bạn cùng tham khảo nội dung chi tiết.

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Communication Systems Lecturer: M.E. P.T.A. Quang .Contents           Chapter 1: Introductory Concepts Chapter 2: QoS Chapter 3: Transmission and switching Chapter 4: Digital networks Chapter 5: Signaling Chapter 6: PSTN Chapter 7: VoIP Chapter 8: Mobile communication Chapter 9: Satellite communication Chapter 10: Fiber-optic communication .

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The concept of trunking began with the telephone industry. • Multiple calls were moved between customers and central offices or between the offices themselves over a single physical connection.The same principle was applied to data communications to make better use of the communication line. • Additional advantages and cost savings were gained by using the same line for voice communications.The same principle of trunking is applied to network switching technologies. • A trunk is a physical and logical connection between two switches across which network traffic travels....

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(Dùng cho sinh viên hệ đào tạo đại học từ xa) UNIT 1 Exercise 1. Read the following passage then answer the questions. ANALOGUE AND DIGITAL NETWORKS Digital technology in the telephone network is nothing new. Take all the relays in older exchanges as an example. Relays are either "off" or "on", and there is no state in between these. Suitable combinations of relays could build up and "remember" numbers - perhaps a far-fetched example, but in was digital, so it will serve!...

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Communications is a process by which information is exchanged between individuals through a common system of symbols, signs, or behaviour “It is about communication between people; the rest is technology” Communication systems are reliable, economical and efficient means of communications Public switched telephone network (PSTN), mobile telephone communication (GSM, 3G, 4G...), broadcast radio or television, navigation systems, ... The course is aiming at introducing fundamental issues required for understanding and designing a (digital) communication system...

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1.Connect devices that are separated by a broader geographical area. 2.Use the services of carriers, such as telephone companies, network providers… 3.Use serial connections.A VPN is an encrypted connection between private networks over a public network such as the Internet. Instead of using a dedicated Layer 2 connection such as a leased line, a VPN uses virtual connections called VPN tunnels, which are routed through the Internet from the private network of the company to the remote site or employee host.

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Telephone networks use circuit switching. The telephone network had its beginnings in the late 1800s. The entire network, which is referred to as the plain old telephone system (POTS), was originally an analog system using analog signals to transmit voice.

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Simplex One direction e.g. Television Half duplex Either direction, but only one way at a time e.g. police radio Full duplex Both directions at the same time e.g. telephone

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Throughout history, networks have served as the foundation for connecting humans to one another and their activities. Roads were laid, bridges built, and waterways crossed so that humans, be they on foot, on animal, or vehicle could traverse physical distance. The airways were conquered through flight. Communications, in turn, were conducted using the available means of the period, from smoke signals, drum beats, and pigeons, to the telegraph, telephone, and computer networks of today.

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In the last two decades, wireless communication systems such as cordless phones, paging systems, wireless data networks, satellite-based and cellular mobile systems have been steadily increasing in both popular importance and technological sophistication. The firstgeneration wireless systems were developed in the late 1970s and 1980s and were based on analog technology (such as the Advance Mobile Phone Service (AMPS) by AT&T and Nordic Mobile Telephone (NMT) by Ericsson).

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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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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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SAR Distributions in a Head Model The development of cellular telephones and mobile communication systems has led to a growing awareness of the vital role that wireless systems play in communication networks and the biological effects of EM fields on users. Since cellular hand phones are operated in close proximity to human heads while in use, there has been increasing public concern about the health effects of the human head exposed to EM energy emitted from mobile handset antennas.

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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.

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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.

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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.

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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 network.

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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’.

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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.

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