Broadband CSMA/CD

Broadband CSMA/CD

• The major difference between the baseband and broadband CSMA/CD lies in the collision detection and carrier sensing.
• The worst case collision detection time
  • Baseband: 2a (a: channel propagation delay)
  • broadband: 4a
• Carrier Sensing
  • Baseband: Actually, there is no modulated carrier. Carrier is sensed by detecting the presence of transmission on the channel.
  • Broadband: The station's receiver listens for the presence of a modulated carrier on the outbound channel.
• Collision Detection
  • Baseband: The signal on the cable at the receiver exceeds the maximum voltage (-1.825v) that could be produced by the transceiver alone.
  • Broadband:
    • Bit by bit comparison between transmitted and received data
    • Perform collision detection at the headend of the single cable system. The headend can detect collision by looking for garbled data or higher than expected signal strength.

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