Siemens IEEE802.11 Tutorial page 38

IEEE802.11e: MAC Enhancements
for Quality of Service (HCF)
n
HCF (Hybrid coordination function)
– only usable in infrastructure QoS network configurations
– to be used during both the contention period (CP) and the
contention free period (CFP)
– uses a QoS-aware point coordinator („hybrid coordinator")
• by default collocated with the enhanced access point (QAP)
• uses the point coordinator's higher priority to allocate
transmission opportunities (TxOPs) to stations
– meets predefined service rate, delay and/or jitter
requirements of particular traffic flows.
– Caused long delays in standardization process due to its
complexity
– Recently widely supported „Fast –Track" proposal to come
to a conclusion in TGe
• Most complex functions eliminated, streamlined HCF, ...
WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.ppt Page 38 © Siemens, 2002