Chapter 9 SSID Screen

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.

Table 31 WMM QoS Priorities

PRIORITY LEVEL

DESCRIPTION

voice

Typically used for traffic that is especially sensitive to jitter. Use

(WMM_VOICE)

this priority to reduce latency for improved voice quality.

 

 

 

video

Typically used for traffic which has some tolerance for jitter but

(WMM_VIDEO)

needs to be prioritized over other data traffic.

 

 

 

best effort

Typically used for traffic from applications or devices that lack

(WMM_BEST_EFFORT

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

This is typically used for non-critical traffic such as bulk transfers

(WMM_BACKGROUND

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.

 

 

 

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

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NWA-3500/NWA-3550 User’s Guide