Accton Technology ES4626 - Manual (Page 251)

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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.
Classification: 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
(Weighted Round Robin).
In Profile: Traffic within the QoS policing policy range (bandwidth or burst value) is called
“In Profile".
Out of Profile:
Traffic out the QoS policing policy range (bandwidth or burst value) is
called “Out of Profile".
8.1.1.2 QoS Implementation
To implement Layer 3 switch software QoS, a general, mature reference model
should be given. QoS can not create new bandwidth, but can maximize the adjustment
and configuration for the current bandwidth resource. Fully implemented QoS can
achieve complete management over the network traffic. The following is as accurate as
possible a description of QoS.
The data transfer specifications of IP cover only addresses and services of source
and destination, and ensure correct packet transmission using OSI layer 4 or above
protocols such as TCP. However, rather than provide a mechanism for providing and
protecting packet transmission bandwidth, IP provide bandwidth service by the best effort.
This is acceptable for services like Mail and FTP, but for increasing multimedia business
data and e-business data transmission, this best effort method cannot satisfy the
bandwidth and low-lag requirement.
Based on differentiated service, QoS specifies a priority for each packet at the
ingress. The classification information is carried in Layer 3 IP packet header or Layer 2
802.1Q frame header. QoS provides same service to packets of the same priority, while
offers different operations for packets of different priority. QoS-enabled switch or router
can provide different bandwidth according to the packet classification information, and
can remark on the classification information according to the policing policies configured,
and may discard some low priority packets in case of bandwidth shortage.