ZyXEL Communications IES4005M, User Manual

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IES4005M User’s Guide
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H A P T E R
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QoS
Use these commands to set up Quality of Service (QoS) through DSCP to IEEE 802.1p priority bit
mapping and queuing settings.
22.1 DSCP to Priority Bit Mapping Commands
Use these commands to configure the DSCP to IEEE 802.1p priority bit mapping to allow the IES to
prioritize traffic based on the incoming DSCP value according to the DSCP to IEEE 802.1p mapping
table.
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.
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 6-bit DSCP field which can define up to 64 service levels and
the remaining 2 bits are defined as currently unused (CU). 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.
The DSCP value determines the PHB (Per-Hop Behavior), that each packet gets as it is forwarded
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.
Table 106
DiffServ: differentiated service field
DSCP (6 bits) CU (2 bits)