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Chapter 17 QoS Configuration
17.1 Introduction to QoS
QoS (Quality of S ervice) is a set of capabilities that allow you to create differentiated servic es for network
traffic, thereby providing better service for selected network traffic. QoS is a guarantee for service quality of
consistent and predictable data transfer service to fulfill program requirements. QoS cannot generate extra
bandwidth but provides more effective bandwidth management according to the application requirement and
network management policy.
17.1.1 QoS Terms
CoS: Class of Service, the classification information carried by Layer 2 802.1Q frames, taking 3 bits of the Tag
field in frame header, is called user priority level in the range of 0 to 7.
Figure 17-1-1 CoS priority
ToS: Type of Service, a one-byte field c arried in Layer 3 IP v4 packet header t o symbolize the servic e type of
IP packets. Among ToS field can be IP Precedence value or DS CP value.
Figure 17-1-2 ToS priority
IP Precedence: IP priority. Classification information carried in Layer 3 IP packet header, occupying 3 bits, in
the range of 0 to 7.
DSCP : Differentiated S ervices Code Point, classification information carried in Layer 3 IP packet header,
occupying 6 bits, in the range of 0 to 63, and is downward compatible with IP Precedence.
DSCP -inside: The switch-inside priority configuration, be used to partition priority for the switch-inside data,
range from 0 to 63.
Classi fication: The entry action of QoS, classifying packet traffic according to the classification information
carried in the packet and ACLs.
Policing: Ingress action of QoS that lays down the policing policy and manages the classified packets.
Remark: Ingress action of QoS, perform allowing, degrading or discarding operations to packets according to
the policing policies.
Queuing: Egress QoS action. Put the packets to appropriate egress queues according to the packet CoS
value.
Scheduling: QoS egress action. Configure the weight for eight egress queues WRR (Weight ed Round
Robin).
17-1
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