The Enhanced Distribution Co-ordination Function (EDCF) or also called as Enhanced Distribution Co-ordination Access (EDCA) is the modification of the basic Distributed Co-ordination Function (DCF)  that was developed by the IEEE 802.11 standard’s body initially.

It was developed to provide priority queuing to different traffic classes. To understand the need for EDCA – refer here <Need for EDCF>

The basic mechanism of EDCF (or EDCA) is provided below. The Traffic is segregated into different traffic classes. The below diagram shows how the different traffic classes are segregated into particular queues in WMM/EDCA (Enhanced Distribution Co-ordination Function)

UP – Stands for User Priority – packets categorized by the upper layers

AC – Stands for Access Category.

In the above diagram each Traffic Class is segregated into an access category queue. 802.11 standard defines 4 access categories. They are

• Vo – Voice Access Category – highest priority access category
• Vi – Video Access Category – priority just below voice
• BE – Best Effort Access Category – priority just below video
• Bk – Background Access Category – lowest access category priority

The mapping of different user priorities to Access categories are provided in a tabular form below

EE – Excellent Effort, CL – Controlled load, BE – Best effort, BK – Background, VO – Voice, VI – Video, NC – Network Control

Enhanced Distribution Co-ordination Function EDCF (WMM) – Part 2