USRobotics Instant802 APSDK User Manual
Page 145
Professional Access Point
Administrator Guide
Quality of Service - 145
is automatically sent to this queue.
•
Data 1 (Video)
. High priority queue, minimum delay. Time-sensitive data such as Video and other
streaming media are automatically sent to this queue.
•
Data 2 (Best Effort)
. Medium priority queue, medium throughput and delay. Most traditional IP data is
sent to this queue.
•
Data 3 (Background)
. Lowest priority queue, high throughput. Bulk data that requires maximum through-
put and is not time-sensitive is sent to this queue (FTP data, for example).
Packets in a higher priority queue will be transmitted before packets in a lower priority queue. Interactive
data in the queues labeled "Data 0" and "Data 1" is always sent first, best effort data in "Data 2" is sent
next, and Background (bulk) data in "Data 3" is sent last. Each lower-priority queue (class of traffic) gets
bandwidth that is left over after the higher classes of traffic have been sent. At an extreme end if you have
enough interactive data to keep the access point busy all the time, low priority traffic would never get sent.
Using the QoS settings in the Web User Interface, 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.
EDCF Control of Data Frames and Arbitration Interframe Spaces
Data is transmitted over 802.11 wireless networks in frames. A Frame consists of a discrete portion of data
along with 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.
Note
Wireless traffic travels:
•
Downstream from the access point to the client
•
Upstream from client to access point
•
Upstream from access point to network
•
Downstream from network to access point
With WMM enabled, QoS settings on the Professional Access Point affect the first two of these; down-
stream traffic flowing from the access point to client (access point EDCA parameters) and the
upstream traffic flowing from the client 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 (access point EDCA parameters).
Traffic flow to and from the network is not under control of the QoS settings on the access point.
Note
A Frame is similar in concept to a
, the difference being that a packet operates on the Network
layer (layer 3 in the OSI model) whereas a frame operates on the Data-Link layer (layer 2 in the
model).