Specifications

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3.5.3.3 IP DSCP Priority
Differentiated Services (DiffServ) is a class of service (CoS) model that enhances best-effort
Internet services by differentiating traffic by users, service requirements and other criteria.
Packet are specifically marked, allowing network nodes to provide different levels of service,
as appropriate for video playback, voice calls or other delay-sensitive applications, via priority
queuing or bandwidth allocation.
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-bits unused field and 6-bits DSCP field which
can define up to 64 service levels.
The following figure illustrates the DS field:
The DSCP value is used to identify 64 levels (2
6
=64) of service and determines the forwarding
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.