1. Fundamentals of Data Communications Neil Tang 9/12/2008
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2. 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
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3. Node
Network-Capable Node Architecture
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4. 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
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5. Types of Links Cable: Connect nodes which are close to each other
Leased Lines:
DS1/T Mbps
DS3/T Mbps
STS Mbps
STS-N N * STS-1
T1 bandwidth represents 24 digital voice circuits of 64 kbps each;
T3 is 28 T1s.
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6. Types of Links Last-Mile Links
POTS Kbps (Plain Old Telephone Service)
ISDN Kbps (Integrated Services Digital Network)
xDSL 16Kbps Mbps
(Asymmetric/Symmetric Digital Subscriber Line)
CATV Mbps (Cable Television)
1.554 ─
8.448 Mbps 16
640 Kbps
Local loop
Central
office
Subscriber
premises
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7. Types of Links Wireless Links GSM system CDMA system
WLAN system (IEEE )
WiMAX system (IEEE )
PAN system (IEEE )
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8. 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
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