CSMa Carrier Sense multiple access) CSMA: listen before transmit This is Carrier sensing o If channel sensed idle: transmit entire frame o If channel sensed busy, defer transmission o Human analogy: dont interrupt others If someone else is already transmitting then back off(wait)unti channel is free Wait how long? If collision is detected during transmission then must retransmit the frame When is it retransmitted? 5: DatCSMA (Carrier Sense Multiple Access) CSMA: listen before transmit: This is Carrier Sensing  If channel sensed idle: transmit entire frame  If channel sensed busy, defer transmission  Human analogy: don’t interrupt others! 5: DataLink Layer 5-19 If someone else is already transmitting then back off (wait) until channel is free Wait how long? If collision is detected during transmission then must retransmit the frame When is it retransmitted?