Distributed coordination function
Distributed Coordination Function (DCF) is a mechanism in WLAN (according to IEEE 802.11 ) with which the non- deterministic access of several participants to the radio network is regulated. The DCF mechanism supports voice and multimedia applications in WLANs with regard to performance requirements.
In terms of transmission technology, WLANs in accordance with IEEE 802.11 are a shared media method with CSMA / CA , with which no quality of service features (QoS) can be guaranteed. To ensure the quality of service such as the transmission rate, the transit times, the data loss rate, etc., various coordination functions have been developed, including a. DCF. In an occupied radio network, a subscriber waits at least the time specified in the 802.11 standard , the DIFS and a random waiting time before checking whether the radio network is busy or whether it can send. In addition to the DIFS time, there are also shorter waiting times, SIFS and PIFS .
Since the DCF function does not adequately meet the requirements for quality of service ( QoS ), the Hybrid Coordination Function (HCF) was developed for 802.11e and the DCF function contained therein implemented as a revised EDCF.