ZyXEL Communications ZyXEL ZyAIR NWA-3500 - Manual (Page 92)

Chapter 6 Wireless Configuration
ZyXEL NWA-3500 User’s Guide
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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.
The DSCP value determines the forwarding behavior, the PHB (Per-Hop Behavior), that each
packet gets across the DiffServ network. Based on the marking rule, different kinds of traffic
can be marked for different priorities of forwarding. Resources can then be allocated
according to the DSCP values and the configured policies.
6.3.5 ToS (Type of Service) and WMM QoS
The DSCP value of outgoing packets is between 0 and 255. 0 is the default priority. WMM
QoS checks the DSCP value in the header of data packets. It gives the traffic a priority
according to this number.
In order to control which priority level is given to traffic, the device sending the traffic must
set the DSCP value in the header. If the DSCP value is not specified, then the traffic is treated
as best-effort. This means the wireless clients and the devices with which they are
communicating must both set the DSCP value in order to make the best use of WMM QoS. A
Voice over IP (VoIP) device for example may allow you to define the DSCP value.
The following table lists which WMM QoS priority level the ZyXEL Device uses for specific
DSCP values.
6.4 Spanning Tree Protocol (STP)
STP detects and breaks network loops and provides backup links between switches, bridges or
routers. It allows a bridge to interact with other STP-compliant bridges in your network to
ensure that only one route exists between any two stations on the network.
6.4.1 Rapid STP
The ZyXEL Device uses IEEE 802.1w RSTP (Rapid Spanning Tree Protocol) that allow faster
convergence of the spanning tree (while also being backwards compatible with STP-only
aware bridges). Using RSTP topology change information does not have to propagate to the
root bridge and unwanted learned addresses are flushed from the filtering database. In RSTP,
the port states are Discarding, Learning, and Forwarding.
Table 19 ToS and IEEE 802.1d to WMM QoS Priority Level Mapping
DSCP VALUE WMM QOS PRIORITY LEVEL
224, 192 voice
160, 128 video
96, 0 A
A. The ZyXEL Device also uses best effort for any DSCP value for which
another WMM QoS priority is not specified (255, 158 or 37 for example).
besteffort
64, 32 background