EDCF Control of Data Frames and AIFS 231
Understanding Quality of Service
• Data 3 (Background). Lowest priority queue, high throughput. Bulk data that requires
maximum throughput and is not time-sensitive is sent to this queue (FTP data, for
example).
Using the QoS settings in the AP profile, you can configure Enhanced Distributed Channel
Access (EDCA) parameters that determine how each queue is treated when it is sent by the
access point to the client or by the client to the access point.
Wireless traffic travels:
• Downstream from the access point to the client station
• Upstream from client station to access point
• Upstream from access point to network
• Downstream from network to access point
With WMM enabled, QoS settings on the D-Link Unified Access System affect the first two of
these; downstream traffic flowing from the access point to client station (AP EDCA
parameters) and the upstream traffic flowing from the station to the access point (station
EDCA parameters).
With WMM disabled, you can still set some parameters on the downstream traffic flowing
from the access point to the client station (AP EDCA parameters).
The other phases of the traffic flow (to and from the network) are not under control of the QoS
settings on the AP.
EDCF Control of Data Frames and AIFS
Data is transmitted over 802.11 wireless networks in frames. A frame consists of a discrete
portion of data along with some descriptive meta-information packaged for transmission on a
wireless network.
Each frame includes a source and destination MAC address, a control field with protocol
version, frame type, frame sequence number, frame body (with the actual information to be
transmitted) and frame check sequence for error detection.
The 802.11 standard defines various frame types for management and control of the wireless
infrastructure, and for data transmission. 802.11 frame types are (1) management frames, (2)
control frames, and (3) data frames. Management and control frames (which manage and
control the availability of the wireless infrastructure) automatically have higher priority for
transmission.
802.11e uses interframe spaces to regulate which frames get access to available channels and
to coordinate wait times for transmission of different types of data.
Management and control frames wait a minimum amount of time for transmission; they wait a
short interframe space (SIF). These wait times are built-in to 802.11 as infrastructure support
and are not configurable.
The D-Link Unified Access System supports the Enhanced Distribution Coordination
Function (EDCF) as defined by the 802.11e standard. EDCF, which is an enhancement to the
DCF standard and is based on CSMA/CA protocol, defines the interframe space (IFS) between
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