VLAN, QoS, and Proxy Mobile IP
eDCF

There is bound to be network collisions when sharing the WLAN. Clients communicating on the WLAN at the exact same time cause these collisions. This causes both packets to back off for a random period of time before sending the packets again. Collisions can not be entirely eliminated but keeping them to a minimum will help to preserve WLAN bandwidth.

To help maintain the bandwidth, QoS uses eDCF to allow higher priority traffic first access to the WLAN media. With QoS, instead of backing off for a random period of time, they will back off for a reduced amount of time depending on the packets priority. eDCF allows the higher priority traffic to pass through the Access Point interfaces faster than lower priority traffic.

In Figure , a (0) IFS (Interframe Space) has a shorter back off time, for example, than a voice packet. A (n) IFS has a longer back off time (for example, email packet).

Transmission opportunity (TXOP) is for environments that have a large amount of WLAN traffic going through the access point. High priority packets will only wait a few seconds to retransmit. If the traffic volume is still high, the high priority packet will continue to resend again and again. TXOP will always reserve a place in line for the high priority packets by reserving the first few seconds for high priority packets. This will guarantee higher priority packet handling. If there is not a high priority packet in the queue, that access point addresses the next packet in line. eDCF is also used to assist the process of handling high priority packets.