CSMA Why aloha and slotted aloha are so inefficient? Stations don't check the channel status. They just send out frames without considering whether the channel is free or not, which creates too many collisions In fact it is not difficult for a station to sense the channel status(free or not) CSMA: Carrier Sense Multiple access Stations listen to the channel(carrier sense) Stations knowwhether the channel is free or not Stations transmit only if the channel is free -Collisions become rare Only if two or more stations attempt to transmit at about the same time, collisions could happen 88 CSMA • Why ALOHA and slotted ALOHA are so inefficient? — Stations don’t check the channel status. They just send out frames without considering whether the channel is free or not, which creates too many collisions. • In fact, it is not difficult for a station to “sense” the channel status (free or not). • CSMA: Carrier Sense Multiple Access — Stations listen to the channel (carrier sense) — Stations “know” whether the channel is free or not — Stations transmit only if the channel is free — Collisions become rare • Only if two or more stations attempt to transmit at about the same time, collisions could happen