Chapter 24 Qos Configuration; Introduction To Qos; Qos Terms - Digitalchina Networks DCS-3950 series Manual

DCS-3950 series Ethernet switch manual

Chapter 24 QoS Configuration

24.1 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.

24.1.1 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 24-1 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 24-2 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 Services 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.
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