Quality Of Service; Wmm Qos; Wmm Qos Priorities; Type Of Service (Tos) - ZyXEL Communications G-3000 User Manual

6.3 Quality of Service

This section discusses the Quality of Service (QoS) features available on the ZyXEL Device.

6.3.1 WMM QoS

WMM (Wi-Fi MultiMedia) QoS (Quality of Service) ensures quality of service in wireless
networks. It controls WLAN transmission priority on packets to be sent over the wireless
network.
WMM QoS prioritizes wireless traffic according to the delivery requirements of the individual
and applications. WMM QoS is a part of the IEEE 802.11e QoS enhancement to certified Wi-
Fi wireless networks.
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 ZyXEL Device uses WMM QoS to prioritize traffic streams according to the VLAN or
DSCP information in each packet's header. The ZyXEL Device automatically determines the
priority to use for an individual traffic stream. This prevents reductions in data transmission
for applications that are sensitive to latency (delay) and jitter (variations in delay).

6.3.1.1 WMM QoS Priorities

The following table describes the WMM QoS priority levels that the uses.

6.3.2 Type Of Service (ToS)

Network traffic can be classified by setting the ToS (Type Of Service) values at the data
source (for example, at the ZyXEL Device) so a server can decide the best method of delivery,
that is the least cost, fastest route and so on.

6.3.2.1 DiffServ

DiffServ is a class of service (CoS) model that marks packets so that they receive specific per-
hop treatment at DiffServ-compliant network devices along the route based on the application
types and traffic flow. Packets are marked with DiffServ Code Points (DSCPs) indicating the
level of service desired. This allows the intermediary DiffServ-compliant network devices to
handle the packets differently depending on the code points without the need to negotiate
paths or remember state information for every flow. In addition, applications do not have to
request a particular service or give advanced notice of where the traffic is going.

6.3.2.2 DSCP and Per-Hop Behavior

DiffServ defines a new DS (Differentiated Services) field to replace the Type of Service
(TOS) field in the IP header. The DS field contains a 2-bit unused field and a 6-bit DSCP field
which can define up to 64 service levels. The following figure illustrates the DS field.
DSCP is backward compatible with the three precedence bits in the ToS octet so that non-
DiffServ compliant, ToS-enabled network device will not conflict with the DSCP mapping.
G-3000 Series User's Guide
Chapter 6 Wireless Configuration
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