Transmission & Switching Techniques

Chia sẻ: Cao Van Manh | Ngày: | Loại File: PDF | Số trang:78

Thêm vào BST

Báo xấu

76
lượt xem 6
download

Download Vui lòng tải xuống để xem tài liệu đầy đủ

Transmission: the propagation of a signal, message, or other form of intelligence by any means such as optical fiber, wire, or visual means. Switching: selects the route to the desired destination that the transmitted signal travels by the closing of switches in either the space domain or the time domain or some combinations of the two.

Chủ đề:

Bình luận(0) Đăng nhập để gửi bình luận!

Lưu

Nội dung Text: Transmission & Switching Techniques

Communication Systems Lecturer: M. Eng. P.T.A. Quang
Transmission & Switching Techniques 1. Transmission and Switching definitions 2. Traffic intensity defines size of switches and the capacity of transmission links 3. Transmission 4. Switching techniques
Transmission and switching definitions  Transmission: the propagation of a signal, message, or other form of intelligence by any means such as optical fiber, wire, or visual means.  Switching: selects the route to the desired destination that the transmitted signal travels by the closing of switches in either the space domain or the time domain or some combinations of the two.
Traffic intensity vs size of switch & capacity links  Measurement of telephone traffic A  C T A: traffic flow (Erlang) C: number of calls originated during one hour T: average holding time (hours)
Traffic intensity vs size of switch & capacity links  Blockage, lost calls, and grade of service (GoS)  Example: tel. exchange serves 5000 subscribers, no more than 10% can connect simultaneously. When the number of served subscribers is 500, the subscriber 501th cannot connect. This call is a lost call/ blocked call and that subscriber has met blockage.  GoS express the probability of meeting blockage during Busy hours (BH)
Traffic intensity vs size of switch & capacity links  Example: determine the GoS if there are 345 lines connected for service and 6 blocked calls during BH.
Traffic intensity vs size of switch & capacity links  Availability: a switch has full-availability when each inlet has access to any outlet. Otherwise, limited availability Limited availability Full availability
Traffic intensity vs size of switch & capacity links  Erlang and Poisson Traffic formulas
Transmission  Signals  Cables  Line coding techniques
Signals in communications  A signal is a discrete part of a communication  There are many types of signals, forexample: gesture, make a sign to somebody, symbol, state of a thing or phenomenon, …  How to communicate them ? => format, transport and store  Language is a kind of format for symbol communication.  Television is a kind of format for phenomenon communication.  To transport or store the signals need to be convert to electrical signals
Signals transmission Sự vật hiện Mã hóa Các file văn Mã hóa File đã Mã hóa File đã mã Mã hóa Electrical signals tượng mã hoá hoá kênh bản, hình vẽ ASCII nguồn Đường truyền Sự vật hiện tượng nếu là:  Âm thanh => thông tin audio (telephone, mobilephone)  Hình ảnh & âm thanh => thông tin video (Tivi)  Sự thay đổi của một đại lượng vật lý nào đó => convert to => tín hiệu điện, thông qua các sensors
Signals transmission (cont)  There are four types of electrical transmission, Wire pair, Coaxial cable, Fiber-optic cable and Radio.
Common Concepts 1. Modulation (define, why do we need to modulate a signal for tramsmission?) 2. Analog transmission (define, what are the ways that information content can be transferred ?) 3. Digital transmission (define, what are the ways that information content can be transferred ?) 4. Compare the different between analog and digital transmission.
Charateristics of transmission lines  General characteristics: attenuation (loss), degradation/distortion, delay and noise  To evaluate the quality of transmission line, we use PSN measurement in dB,  Peak _ signal  PSN  20 log   dB  Noise  Nguồn phát Truyền dẫn sóng bằng dây song hành (Transmitter) dx R'dx L'dx IN1 OUT1 G'dx C'dx Skin effect creates a change of the charateristic IN2 OUT2  resistance of the transmission lines
Twisted pair cables Unshielded twisted pair (UTP) Shielded twisted pair (STP)
Twisted pairs charteristics Described in EIA/TIA-568. 10BASE-T and Unsuitable for speeds above 16 16MHz[6] 100BASE-T4 Mbit/s. Now mainly for telephone Ethernet[6] cables[6] UTP[6] 20MHz[6] 16 Mbit/s[6] Token Ring Not commonly used[6] 100BASE-TX & 1000BASE-T UTP[6] 100MHz[6] Common in most current LANs[6] Ethernet[6] Enhanced Cat5. Same construction 100BASE-TX & 1000BASE-T UTP[6] 100MHz[6] as Cat5, but with better testing Ethernet[6] standards. Most commonly installed cable in UTP[6] 250MHz[6] 1000BASE-T Ethernet Finland according to the 2002 standard. SFS-EN 50173-1 250MHz (500MHz Not a standard; a cable maker's according to some) own label. 500MHz 10GBASE-T Ethernet ISO/IEC 11801:2002 Amendment 2. Telephone, CCTV, 1000BASE-TX in Four pairs, U/FTP (shielded pairs). S/FTP[6] 600MHz[6] the same cable. 10GBASE-T Standard under development. Ethernet. Telephone, CATV, 1000BASE-TX in Four pairs, S/FTP (shielded pairs, 1000MHz the same cable. 10GBASE-T braid-screened cable). Standard Ethernet. under development.
Coaxial Cables Range up to 10 GHz for the transmission frequency
Fiber-Optic cables Transfer mode in fiber-optic cables Range up to 100 Petabit per second
On Line Coding Techniques  Line coding design:  A line code is designed to meet several objectives:  Self-synchronization  The ability to recover timing from the signal itself  Long series of ones and zeros could cause a problem  Low probability of bit error  The receiver needs to be able to distinguish the waveform associated with a mark from the wave form associated with a space, even if there is a considerable amount of noise and distortion in the channel  Spectrum that is suitable for the channel  In some cases DC components should be avoided  E.g if the channel has a DC block capacitance  The transmission bandwidth should be minimized
Line encoding process  The input to the line encoder is a sequence of values a that is a function of a data bit (or an ADC output bit).  The output of the line encoder is a waveform: x(t )   ak p(t  kTb )  where p(t) is the pulse shape and T is the bit period k  The operational details of this function are set by the particular type of line code that is being used.