Random Access Protocols

• Fundamentally different approach.

• Aloha at Univ of Hawaii: Transmit whenever you like. Random retransmission time.Worst case utilization = 1/(2e) =18%

• Slotted Aloha: Fixed size transmission slotsWorst case utilization = 1/e = 37%

• CSMA: Carrier Sense Multiple Access Listen before you transmit

• CSMA/CD: CSMA with Collision DetectionListen while transmitting. Stop if you hear someone else

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