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Chapter 13 QoS Configuration
13.1 QoS
13.1.1 Introduction to QoS
QoS (Quality of Service) is a set of capabilities that allow you to create differentiated
services 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.
13.1.1.1 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.
Fig 13-1 CoS priority
ToS: Type of Service, a one byte field carried in Layer 3 IPv4 packet header to symbolize
the service type of IP packets. Among ToS field can be IP Precedence value or DSCP
value.
Fig 13-2 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.