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122 AT-TQ2403 - Management Software - User's Guide
802.11e and WMM Standards Support
QoS describes a range of technologies for controlling data streams on shared network connections. The
IEEE 802.11e task group has defined a QoS standard for transmission quality and availability of service on
wireless networks. QoS is designed to provide better network service by limiting Jitter, Latency, and
Packet Loss; supporting dedicated bandwidth for time-sensitive or mission critical applications, and
prioritizing wireless traffic for channel access.
As with all IEEE 802.11 working group standards, the goal is to provide a standard way of implementing
QoS features so that components from different companies are interoperable.
The AT-TQ2403 Management Software provides QoS based on the Wi-Fi Wireless Multimedia (WMM)
specification which are implementations of a subset of 802.11e features.
Both access points and wireless clients (laptops, consumer electronics products) can be WMM-enabled
by the Wi-Fi Alliance.
QoS Queues and Parameters to Coordinate Traffic Flow
Configuring QoS options on the AT-TQ2403 Management Software consists of setting parameters on
existing queues for different types of wireless traffic. You can configure different minimum and maximum
wait times for the transmission of packets in each queue based on the requirements of the media being
sent. Queues automatically provide minimum transmission delay for Voice, Video, multimedia, and
mission critical applications, and rely on best-effort parameters for traditional IP data.
For example, time-sensitive Voice, Video, and multimedia are given effectively higher priority for
transmission (lower wait times for channel access), while other applications and traditional IP data which
are less time-sensitive but often more data-intensive are expected to tolerate longer wait times.
The AT-TQ2403 Management Software implements QoS based on the IEEE Wireless Multimedia
(WMM) standard. A Linux-based queuing class is used to tag packets and establish multiple queues. The
queues provided offer built-in prioritization and routing based on the type of data being transmitted.
The Administration UI provides a way for you to configure parameters on the queues.
QoS Queues and Diff-Serv Code Point (DSCP) on Packets
QoS on the AT-TQ2403 Management Software leverages WMM information in the IP packet header
related to Diff-Serv Code Point (DSCP). Every IP packet sent over the network includes a DSCP field in
the header that indicates how the data should be prioritized and transmitted over the network. The
DSCP field consists of a 6 bit value defined by the local administration. For WMM, Wi-Fi Alliance
suggests a particular mapping for DSCP values. For more information see “VLAN Priority
”.
The access point examines the DSCP field in the headers of all packets that pass through the AP. Based
on the value in a packet’s DSCP 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 priorities 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