Thomas Kunz
Systems and Computer Engineering
208
HIPERLAN 1 CAC Sublayer
nChannel Access Control (CAC)
–assure that
terminal does not access forbidden channels
–priority
scheme, access with EY-NPMA
nPriorities
–5 priority
levels for QoS support
–QoS is
mapped onto a priority level with the help of the packet lifetime (set by an application)
nif packet lifetime = 0 it makes no sense to forward the
packet to the receiver any longer
nstandard start value 500ms, maximum 16000ms
nif a terminal cannot send the packet due to its current
priority, waiting time is permanently
subtracted from lifetime
nbased on packet lifetime, waiting time in a sender and
number of hops to the receiver, the
packet is assigned to one out of five priorities
nthe priority of waiting packets, therefore, rises
automatically