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Psion Teklogix 9160 G2 Wireless Gateway User Manual 185
Chapter 19: Quality of Service (QoS)
QoS Queues And Parameters To Coordinate Traffic Flow
with each bit representing a different aspect or degree of priority for this data as well
as other meta-information (low delay, high throughput, high reliability, low cost,
and so on).
For example, the ToS for FTP data packets is likely to be set for maximum through-
put since the critical consideration for FTP is the ability to transmit relatively large
amounts of data in one go. Interactive feedback is a nice-to-have in this situation but
certainly less critical. VoIP data packets are set for minimum delay because that is a
critical factor in quality and performance for that type of data.
The access point examines the ToS field in the headers of all packets that pass
through the AP. Based on the value in a packet’s ToS field, the AP prioritizes the
packet for transmission by assigning it to one of the queues. This process occurs
automatically, regardless of whether you deliberately configure QoS or not.
A different type of data is associated with each queue. The queue and associated pri-
orities and parameters for transmission are as follows:
• Data 0 (Voice). Highest priority queue, minimum delay. Time-sensitive data
such as Voice over IP (VoIP) 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 throughput 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 pri-
ority queue. Interactive data in the queues labelled “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 on the Administration UI, you can configure Enhanced Dis-
tributed 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.