DFWMAC-DCF CSMA/CA with RTS/CTS Transmitter sends an RTS(Request To Send) after medium has been idle for time interval more than dIFS Receiver responds with CTS (Clear To Send) after medium has been idle for siFs Then data is transmitted RTSICTS is used for reserving channel for data transmission so that the collision can only occur in control message CS5602: Principles and Techniques for Sensors and Information Perception
DFWMAC-DCF CSMA/CA with RTS/CTS ▪ Transmitter sends an RTS (Request To Send) after medium has been idle for time interval more than DIFS. ▪ Receiver responds with CTS (Clear To Send) after medium has been idle for SIFS. ▪ Then data is transmitted. ▪ RTS/CTS is used for reserving channel for data transmission so that the collision can only occur in control message. CS5602: Principles and Techniques for Sensors and Information Perception 31
DEWMAC-DCF CSMA/CA with RTS/CTs Use short signaling packets for Collision Avoidance RTS (Request To Send) Packet(20 Bytes) A sender requests the right to send from a receiver with a short RTS packet before it sends a data packet a CTS (Clear To Send) Packet (16 Bytes) The receiver grants the right to send as soon as it is ready to receive They contain:(Sender Address; Receiver Address; Packet Size) CS5602: Principles and Techniques for Sensors and Information Perception
DFWMAC-DCF CSMA/CA with RTS/CTS ▪ Use short signaling packets for Collision Avoidance ▪ RTS (Request To Send) Packet (20 Bytes): A sender requests the right to send from a receiver with a short RTS packet before it sends a data packet ▪ CTS (Clear To Send) Packet (16 Bytes): The receiver grants the right to send as soon as it is ready to receive They contain: (Sender Address; Receiver Address; Packet Size) CS5602: Principles and Techniques for Sensors and Information Perception 32
DFWMAC-DCF CSMA with RTS/CTS DIFS SIFS Date ime RTS S ource SIFS Destination cTs ACK pIFS I Contention window Other Next frame Defer access Backoff After Defer CS5602: Principles and Techniques for Sensors and Information Perception
DFWMAC-DCF CSMA with RTS/CTS CS5602: Principles and Techniques for Sensors and Information Perception 33 DIFS Next Frame CTS RTS Other Source Destination DIFS SIFS Contention Window Defer Access Backoff After Defer SIFS Data SIFS ACK Time
Problems with cSMaca Hidden terminal problem - Exposed terminal problem CS5602: Principles and Techniques for Sensors and Information Perception
Problems with CSMA/CA ▪Hidden terminal problem ▪Exposed terminal problem CS5602: Principles and Techniques for Sensors and Information Perception 34
Hidden Terminal problem RTS B cTs DATA A sends rts B sends cts C overhears CTs C inhibits its own transmitter A successfully sends Data to B CS5602: Principles and Techniques for Sensors and Information Perception
Hidden Terminal Problem ▪ A sends RTS ▪ B sends CTS ▪ C overhears CTS ▪ C inhibits its own transmitter ▪ A successfully sends DATA to B CS5602: Principles and Techniques for Sensors and Information Perception 35 A B C RTS DATA CTS CTS