ZyXEL Communications NWA-3550, User Manual

Page: 150 / 408

Chapter 9 SSID Screen
NWA-3500/NWA-3550 User’s Guide
150
On APs without WMM QoS, all traffic streams are given the same access priority to
the wireless network. If the introduction of another traffic stream creates a data
transmission demand that exceeds the current network capacity, then the new
traffic stream reduces the throughput of the other traffic streams.
The NWA uses WMM QoS to prioritize traffic streams according to the IEEE 802.1q
or DSCP information in each packet’s header. The NWA automatically determines
the priority to use for an individual traffic stream. This prevents reductions in data
transmission for applications that are sensitive to latency and jitter (variations in
delay).
9.3.1.1 WMM QoS Priorities
The following table describes the WMM QoS priority levels that the NWA uses.
9.3.2 ATC
Automatic Traffic Classifier (ATC) is a bandwidth management tool that prioritizes
data packets sent across the network. ATC assigns each packet a priority and then
queues the packet accordingly. Packets assigned a high priority are processed
more quickly than those with low priority if there is congestion, allowing time-
sensitive applications to flow more smoothly. Time-sensitive applications include
both those that require a low level of latency and a low level of jitter such as Voice
over IP or Internet gaming, and those for which jitter alone is a problem such as
Internet radio or streaming video.
ATC assigns priority based on packet size, since time-sensitive applications such
as Internet telephony (Voice over IP or VoIP) tend to have smaller packet sizes
than non-time sensitive applications such as FTP (File Transfer Protocol). The
following table shows some common applications, their time sensitivity, and their
Table 31 WMM QoS Priorities
PRIORITY LEVEL DESCRIPTION
voice
(WMM_VOICE)
Typically used for traffic that is especially sensitive to jitter. Use
this priority to reduce latency for improved voice quality.
video
(WMM_VIDEO)
Typically used for traffic which has some tolerance for jitter but
needs to be prioritized over other data traffic.
best effort
(WMM_BEST_EFFORT
)
Typically used for traffic from applications or devices that lack
QoS capabilities. Use best effort priority for traffic that is less
sensitive to latency, but is affected by long delays, such as
Internet surfing.
background
(WMM_BACKGROUND
)
This is typically used for non-critical traffic such as bulk transfers
and print jobs that are allowed but that should not affect other
applications and users. Use background priority for applications
that do not have strict latency and throughput requirements.