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

Physical Layer 1b-2 Outline  Theoretical basis m Fourier analysis and bandwidth-limited signals  Physical media m Guided (copper, fibre) m Unguided (wireless)  Modulation  Multiplexing

Physical Layer 1b-3 Bandwidth-Limited Signals (a) binary signal and its root-mean-square Fourier amplitudes. (b) – (c) Successive approximations to the original signal.

Physical Layer 1b-4 Bandwidth-Limited Signals (2) (d) – (e) Successive approximations to the original signal.

Physical Layer 1b-5 Physical Media  Bit: propagates between transmitter/rcvr pairs  physical link: what lies between transmitter & receiver  guided media: m signals propagate in solid media: copper, fiber, coax  unguided media: m signals propagate freely, e.g., radio

Physical Layer 1b-6 Twisted Pair  two insulated copper wires m Category 3: phone wires, 10 Mbps Ethernet m Category 5: 100Mbps Ethernet

Physical Layer 1b-7 Coaxial Cable  two concentric copper conductors  bidirectional  baseband: m single channel on cable m legacy Ethernet  broadband: m multiple channel on cable m HFC

Physical Layer 1b-8 Fiber Optic Cable  glass fiber carrying light pulses, each pulse a bit  high-speed operation: m high-speed point-to-point transmission (e.g., 10 Gps)  low error rate: repeaters spaced far apart; immune to electromagnetic noise

Physical Layer 1b-9 Optical Transmission

Physical Layer 1b-10 Fiber Cables (a) Side view of a single fiber. (b) End view of a sheath with three fibers.

Physical Layer 1b-11 Wireless  signal carried in electromagnetic spectrum  no physical “wire”  bidirectional  propagation environment effects: m reflection m obstruction by objects m interference Wireless link types:  terrestrial microwave m e.g. up to 45 Mbps channels  LAN (e.g., Wifi) m 2Mbps, 11Mbps  wide-area (e.g., cellular) m e.g. 3G: hundreds of kbps  satellite m up to 50Mbps channel (or multiple smaller channels)

Physical Layer 1b-12 The Electromagnetic Spectrum

Physical Layer 1b-13 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 1b-14 Free-Space Optics Convection currents can interfere with laser communication systems.

Physical Layer 1b-15 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 1b-16 Low-Earth Orbit Satellites: Iridium (a) The Iridium satellites from six necklaces around the earth. (b) 1628 moving cells cover the earth.

Physical Layer 1b-17 Modulation / Demodulation (a) A binary signal (b) Amplitude modulation (c) Frequency modulation (d) Phase modulation

Physical Layer 1b-18 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 1b-19 Frequency Division Multiplexing (a) The original bandwidths. (b) The bandwidths raised in frequency. (b) The multiplexed channel.

Physical Layer 1b-20 Time Division Multiplexing The T1 carrier (1.544 Mbps).

Physical Layer 1b-21 Wavelength Division Multiplexing