CSMA/CA Algorithm If Collisions(Control or Data) Binary exponential increase(doubling) of CW; Length of backoff time is exponentially increased as the station goes through successive transmissions CS5602: Principles and Techniques for Sensors and Information Perception
CSMA/CA Algorithm ▪ If Collisions (Control or Data) ▪→ Binary exponential increase (doubling) of CW; Length of backoff time is exponentially increased as the station goes through successive retransmissions. CS5602: Principles and Techniques for Sensors and Information Perception 21
Inter-frame Spaces(IFs) DIFS DIFS PIFS Medium Busy Backoff Window Nex↑ Frame Direct access if medium is free≥DTFs CS5602: Principles and Techniques for Sensors and Information Perception
Inter-frame Spaces (IFS) CS5602: Principles and Techniques for Sensors and Information Perception 22 t Medium Busy SIFS PIFS DIFS DIFS Next Frame Backoff Window Direct access if medium is free DIFS
Inter-frame Spaces(IFS) Priorities are defined through different inter frame spaces SIFS (Short Inter Frame Spacing) Highest priority packets such as ACK, CTS, polling response Used for immediate response actions CS5602: Principles and Techniques for Sensors and Information Perception
Inter-frame Spaces (IFS) ▪ Priorities are defined through different inter frame spaces ▪SIFS (Short Inter Frame Spacing) ▪Highest priority packets such as ACK, CTS, polling response ▪Used for immediate response actions CS5602: Principles and Techniques for Sensors and Information Perception 23
Inter-frame Spaces(IFS) PIFS(PCF IFS)-Point Coordination Function Inter Frame spacing Medium priority, for real time service using PCF SIFS One slot time Used by centralized controller in PcF scheme when using polls CS5602: Principles and Techniques for Sensors and Information Perception
Inter-frame Spaces (IFS) ▪ PIFS (PCF IFS) - Point Coordination Function InterFrame spacing ▪Medium priority, for real time service using PCF ▪SIFS + One slot time ▪Used by centralized controller in PCF scheme when using polls CS5602: Principles and Techniques for Sensors and Information Perception 24
Inter-frame Spaces(IFS) DIFS (DCF, Distributed Coordination Function IFS Lowest priority, for asynchronous data service SFS Two slot times Used as minimum delay of asynchronous frames contending for access CS5602: Principles and Techniques for Sensors and Information Perception
Inter-frame Spaces (IFS) ▪ DIFS (DCF, Distributed Coordination Function IFS) ▪Lowest priority, for asynchronous data service ▪SFIS + Two slot times ▪Used as minimum delay of asynchronous frames contending for access CS5602: Principles and Techniques for Sensors and Information Perception 25