Chapter 19: Quality of Service (QoS)
QoS Queues And Parameters To Coordinate Traffic Flow
186 Psion Teklogix 9160 G2 Wireless Gateway User Manual
Note: 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 9160 G2 Wirel ess Gat eway a ffe ct
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 parameters on the downstr eam t raffic
flowing from the AP 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.
19.1.3.2 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 some descriptive meta-information packaged for
transmission on a wireless network.
Note: A Frame is similar in concept to a Packet, 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 OSI model).
Each frame includes a source and destination MAC address, a control field with pro-
tocol 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 contr ol of the
wireless infrastructure, and for data transmission. 802.11 frame types are: (1) man-
agement 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.