DATA COMMUNICATION Lecture-24

Recap of Lecture 23 MODEM Standards Bell Modems ITU-T Modems Traditional Modems 56k Modems

Overview of Lecture 24 Cable Modems Electromagnetic Spectrum Transmission Media and its Types Guided Media Twisted Pair Coaxial Cable Optical Fiber

Cable Modem Cable TV uses a coaxial cable Bandwidth up to 750 MHz (cf. 4KHz telephone line) Each band is 6MHz; Multiplexed by FDM

Cable Modem

Cable Modem Downloading Uploading 64-QAM: 6 MHz * 6 bits/baud = 36 Mbps maximum Uploading Uploading band uses lower frequency range: Noisy QPSK: 6 MHz * 2 bits/baud = 12 Mbps maximum

Electromagnetic Energy Signals are transmitted in the form of electromagnetic energy, which can travel through Metal cables (voice-band frequency) Air/space (radio frequency) Fiber-optic cable (visible light)

Electromagnetic Spectrum

Classes of Transmission Media

Categories of Guided Media

Twisted-Pair Cable Two forms Unshielded twisted-pair (UTP) Shielded twisted-pair (STP)

Frequency of Twisted-Pair Cable

Unshielded Twisted-Pair (UTP) Cable

Parallel Flat Wire

Noise Effect on Twisted-Pair

Advantage of UTP Advantages of UTP are: Cost Ease of Use

UTP Cable

Categories of UTP Cable Category 1 Category 2 Category 3 Category 4 Category 5

UTP Connectors

Summary Cable Modems Electromagnetic Spectrum Transmission Media and its Types Guided Media Twisted Pair Coaxial Cable Optical Fiber

Suggested Reading Section 6.6, 7.1, “Data Communications and Networking” 2nd Edition by Behrouz A. Forouzan