Fundamentals of Data Communications Neil Tang 9/12/2008 CS440 Computer Networks

Major Issues Encoding: Encode binary data to physical signals Framing: Delineate bit stream into messages or frames Error detection: Identify corrupted frames Reliability: Frame-level reliability Media access control: Resolve contentions CS440 Computer Networks

Node Network-Capable Node Architecture CS440 Computer Networks

Link Different physical media: twisted pair, coaxial cable, optical fiber, space. Signals always propagate in a physical medium in the form of electromagnetic waves. Full Duplex and Half Duplex Spectrum allocation CS440 Computer Networks

Types of Links Cable: Connect nodes which are close to each other Leased Lines: DS1/T1 1.544 Mbps DS3/T3 44.736 Mbps STS-1 151.840 Mbps STS-N N * STS-1 T1 bandwidth represents 24 digital voice circuits of 64 kbps each; T3 is 28 T1s. CS440 Computer Networks

Types of Links Last-Mile Links POTS 28.8 - 56 Kbps (Plain Old Telephone Service) ISDN 64 - 128 Kbps (Integrated Services Digital Network) xDSL 16Kbps - 55.2 Mbps (Asymmetric/Symmetric Digital Subscriber Line) CATV 20-40 Mbps (Cable Television) 1.554 ─ 8.448 Mbps 16 640 Kbps Local loop Central office Subscriber premises CS440 Computer Networks

Types of Links Wireless Links GSM system CDMA system WLAN system (IEEE 802.11) WiMAX system (IEEE 802.16) PAN system (IEEE 802.15.1) CS440 Computer Networks

Shannon’s Theorem C = B log2(1 + S/N) C: Capacity (maximum data rate), B: Spectrum Bandwidth, S/N: Signal/Noise For example, if B = 3 kHz, dB = 10 log10(S/N), so S/N = 1000 = 30 dB C = 3000 log2(1001) ≈30 kbps CS440 Computer Networks