QoS Configuration
IP precedence contains 8 formats.
Table 20-2 Description on IP Precedence
TOS precedence contains 5 formats.
Table 20-3 Description on TOS Precedence
According to RFC 2474, the ToS field is redefined as the differentiated services (DS) field,
where a DSCP value is represented by the first six bits (0 to 5) and ranges from 0 to 63. The
remaining two bits (6 and 7) are reserved.
Figure 20-3 DSCP values
In a network in the Diff-Serve model, traffic is grouped into the following classes, and
packets are processed according to their DSCP values
Expedited forwarding (EF) class: In this class, packets are forwarded regardless of link
share of other traffic. The class is suitable for preferential services requiring low delay, low
packet loss, low jitter, and high bandwidth.
Assured forwarding (AF) class: This class is divided into four subclasses (AF 1 to AF 4),
each containing three drop priorities for more granular classification. The QoS level of the AF
class is lower than that of the EF class.
Class selector (CS) class: This class is derived from the IP ToS field and includes eight
subclasses.
Best effort (BE) class: This class is a special CS class that does not provide any assurance.
AF traffic exceeding the limit is degraded to the BE class. All IP network traffic belongs to this
class by default.
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