User's Manual

18-1
Chapter 18 QoS Configuration
18.1 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.
18.1.1 QoS Terms
QoS: Quality of Service, provides a guarantee for service quality of consistent and predictable data transfer
service to fulfill program requirements. QoS cannot generate new bandwidth but provides more effective
bandwidth management according to the application requirement and network management.
QoS Domain: QoS Domain supports QoS devices to form a net-topology that provides Quality of Service, so
this topology is defined as QoS Domain.
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 18-1 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.
Figure 18-2 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.
Internal Priority: The internal priority setting of the switch chip, it’s valid range relates with the chip, it’s
shortening is Int-Prio or IntP.