2012 session 1 TELE3118: Network Technologies Week 1: Physical Layer Some slides have been taken from: Computer Networking: A Top Down Approach Featuring the Internet, 3rd edition. Jim Kurose, Keith Ross. Addison-Wesley, July 2004. All material copyright 1996-2004. J.F Kurose and K.W. Ross, All Rights Reserved. Computer Networks, 4th edition. Andrew S. Tanenbaum. Prentice-Hall, 2003. Physical Layer

Outline Theoretical basis Physical media Modulation Multiplexing Fourier analysis and bandwidth-limited signals Physical media Guided (copper, fibre) Unguided (wireless) Modulation Multiplexing Physical Layer

Bandwidth-Limited Signals (a) binary signal and its root-mean-square Fourier amplitudes. (b) – (c) Successive approximations to the original signal. Physical Layer

Bandwidth-Limited Signals (2) (d) – (e) Successive approximations to the original signal. Physical Layer

Physical Media Bit: propagates between transmitter/rcvr pairs physical link: what lies between transmitter & receiver guided media: signals propagate in solid media: copper, fiber, coax unguided media: signals propagate freely, e.g., radio Physical Layer

Twisted Pair two insulated copper wires Category 3: phone wires, 10 Mbps Ethernet Category 5: 100Mbps Ethernet Physical Layer

Coaxial Cable two concentric copper conductors bidirectional baseband: single channel on cable legacy Ethernet broadband: multiple channel on cable HFC Physical Layer

Fiber Optic Cable glass fiber carrying light pulses, each pulse a bit high-speed operation: high-speed point-to-point transmission (e.g., 10 Gps) low error rate: repeaters spaced far apart; immune to electromagnetic noise Physical Layer

Optical Transmission Physical Layer

Fiber Cables (a) Side view of a single fiber. (b) End view of a sheath with three fibers. Physical Layer

Wireless Wireless link types: terrestrial microwave e.g. up to 45 Mbps channels LAN (e.g., Wifi) 2Mbps, 11Mbps wide-area (e.g., cellular) e.g. 3G: hundreds of kbps satellite up to 50Mbps channel (or multiple smaller channels) signal carried in electromagnetic spectrum no physical “wire” bidirectional propagation environment effects: reflection obstruction by objects interference Physical Layer

The Electromagnetic Spectrum Physical Layer

Radio Transmission (a) In the VLF, LF, and MF bands, radio waves follow the curvature of the earth. (b) In the HF band, they bounce off the ionosphere. Physical Layer

Free-Space Optics Convection currents can interfere with laser communication systems. Physical Layer

Communication Satellites Communication satellites and some of their properties, including altitude above the earth, round-trip delay time and number of satellites needed for global coverage. Physical Layer

Low-Earth Orbit Satellites: Iridium (a) The Iridium satellites from six necklaces around the earth. (b) 1628 moving cells cover the earth. Physical Layer

Modulation / Demodulation (a) A binary signal (b) Amplitude modulation (c) Frequency modulation (d) Phase modulation Physical Layer

Modems (a) Quadrature Phase-Shift Keying: QPSK (b) Quadrature Amplitude Modulation: QAM-16 (c) QAM-64 Baud-rate: symbols/sec Bit-rate = baud-rate x bits/symbol Physical Layer

Frequency Division Multiplexing (a) The original bandwidths. (b) The bandwidths raised in frequency. (b) The multiplexed channel. Physical Layer

Time Division Multiplexing The T1 carrier (1.544 Mbps). Physical Layer

Wavelength Division Multiplexing Physical Layer