Csmaca
- 1. Carrier Sense Multiple Access with Collision Avoidance The wireless client senses the media Can a signal be detected? If the media is free the client sends data to the access point If the media is not free the client waits The access point receives the data and sends an acknowledgement back to the client If no acknowledgement is received the client resends the data Multiple Access means the media (the service area air space) is shared with other wireless devices Collision Avoidance means that devices listen before sending to avoid collisions Hidden Node problem means that collisions cannot always be detected by all devices
- 2. Hidden Node Problem RF signals loose energy and become weaker as they move away from the transmitter A wireless device transmitting from the outer edge of signal range from the access point will not be able to detect a signal from a wireless device transmitting from the opposite edge of signal range RTS/CTS Request to send/clear to send To avoid the hidden node problem, the wireless device requests the medium and the access point allocates the medium to the device until its transmission has ended
- 3. The process for sending frames is: Create frame Listen before sending, if no signal then Send RTS request to send to Access Point Wait for CTS clear to send from Access Point If CTS is received then transmit data If CTS is not received wait for random back-off time Return to listen before sending Look at the flow chart on: http://en.wikipedia.org/wiki/Carrier_sense_multiple_access_with_collision_avoidanc e