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QoS Configuration
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Fig 20-2 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.
Drop Precedence:
When processing the packets, firstly drop the packets with the bigger
drop precedence, the ranging is 0-1.
It‘s shortening is Drop-Prec or DP.
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.
Scheduling:
QoS egress action. Add the packets to the corresponding egress queue
according to the internal priority. And then decide sending and dropping according to Drop
Precedence, sending algorithm and queue weight of egress queue.
20.1.2
QoS Implementation
To implement the 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
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