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Contents • Communications Theory – Parallel vs. serial transmission – Transmission Capacity (Shannon) – Error detection and correction • Communications Media – Optical fibers – Coaxial cables – Twisted pairs – Wireless Postacademic Interuniversity Course in Information Technology – Module C1 p1 Snell’s Law sin 1 sin 2 2 n2 n1 n2 n1 1 = n2 n1 n2 n1 c >c n2 < n1 Postacademic Interuniversity Course in Information Technology – Module C1 p2 Optical Fibers (step index) n2 < n1 n2 n1 Protective coating Postacademic Interuniversity Course in Information Technology – Module C1 p3 Multimode Fiber Diameter : > 50 Step index fiber Graded index fiber Low cost but limited bandwidth * distance due to multimode dispersion Postacademic Interuniversity Course in Information Technology – Module C1 p4 Multimode Dispersion t t Step index fiber : < 50 MHz.Km Graded Index Fiber : < 1000 MHz.Km (1990) < 5000 MHz.Km (2000) Postacademic Interuniversity Course in Information Technology – Module C1 p5 Monomode Fiber Diameter : < 5 Only one propagation mode possible Higher cost due to end equipment but enormous bandwidth*distance product 10 Gb/s over 500 Km optical sections (1995) Postacademic Interuniversity Course in Information Technology – Module C1 p6 Wave Domain Multiplexing Each color can carry an independent data flow. In 2000 40 colors carrying each 10 Gb/s or 80 colors carrying each 2.5 Gb/s were commercially available Postacademic Interuniversity Course in Information Technology – Module C1 p7 Optical amplifiers Pump laser Erbium doped fiber Erbium atoms are pumped into a higher energy state by the light of the pump laser, they fall back in synchronism with the incoming light, amplifying it. Postacademic Interuniversity Course in Information Technology – Module C1 p8 Optical Switching From IEEE Com.Mag.V39,N1, Jan 2001. Postacademic Interuniversity Course in Information Technology – Module C1 p9 Contents • Communications Theory – Parallel vs. serial transmission – Transmission Capacity (Shannon) – Error detection and correction • Communications Media – Optical fibers – Coaxial cables – Twisted pairs – Wireless Postacademic Interuniversity Course in Information Technology – Module C1 p10 Coaxial Cables Insulator Conductor Conductor Protective coating Monomode propagation for all data applications Transmission rates up to some Gb/s Distance limited by electrical attenuation Postacademic Interuniversity Course in Information Technology – Module C1 p11 Contents • Communications Theory – Parallel vs. serial transmission – Transmission Capacity (Shannon) – Error detection and correction • Communications Media – Optical fibers – Coaxial cables – Twisted pairs – Wireless Postacademic Interuniversity Course in Information Technology – Module C1 p12 Twisted Pairs Performance highly dependant on cable quality Transmission speed up to several 100 Mb/s for distances of up to 100 m. with better cables (class 5 or 6) Postacademic Interuniversity Course in Information Technology – Module C1 p13