Mobile agents in WSN - Most IEEE 802.11 WLANs use the contention‐based channel mechanisms known as DCF or enhanced distributed channel access (EDCA); in both of which, nodes attempt medium access after a random backoff period during which the medium is free. In addition, EDCA allows traffic to be prioritized through differentiation of contention window interframe space and duration of transmission opportunity. Still, this approach is not well suited for real‐time traffic, which is better served through HCCA, typically used to achieve quality of service (QoS) for real‐time multimedia services or to improve energy efficiency.

The HCF is composed of two access methods: contention‐based channel access through EDCA and controlled channel access through HCCA. HCCA can start the controlled channel access mechanism in both contention‐free period (CFP) and contention period (CP) intervals. During the CP, a new contention‐free subperiod named controlled access phase (CAP) is introduced, in which frames are transmitted using HCCA. HCCA can start a CAP by sending downlink QoS frames or QoS CP‐poll frames to allocate polled transmission opportunity to different QSTAs after the medium remains idle for at least point coordination function interframe space interval; the remaining time of the CP can be used by EDCA. This contention‐free scheme is fairly flexible, which is why CFP is made optional in the 802.11e standard 29.