ZyXEL Communications NWA3550 - Manual (Page 93)

Chapter 7 Wireless Configuration
NWA3550 User’s Guide
93
7.3.1.1 WMM QoS Priorities
The following table describes the WMM QoS priority levels that the ZyXEL Device uses.
7.3.2 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 typical data packet sizes. Note that the figures
given are merely examples - sizes may differ according to application and circumstances.
When ATC is activated, the device sends traffic with smaller packets before traffic with larger
packets if the network is congested.
ATC assigns priority to packets as shown in the following table.
Table 14 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.
Table 15 Typical Packet Sizes
APPLICATION
TIME
SENSITIVITY
TYPICAL PACKET SIZE
(BYTES)
Voice over IP (SIP) High < 250
Online Gaming High 60 ~ 90
Web browsing (http) Medium 300 ~ 600
FTP Low 1500
Table 16 Automatic Traffic Classifier Priorities
PACKET SIZE (BYTES) ATC PRIORITY
1 ~ 250 ATC_High
250 ~ 1100 ATC_Medium
1100 + ATC_Low