3Com 3CR17660-91, Configuration Manual

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216 C
HAPTER
27: Q
O
S C
ONFIGURATION
The precedence is called 802.1p priority because the related applications of this
precedence are defined in detail in the 802.1p specification.
Priority Remark The priority remark function is to use ACL rules in traffic identifying and remark the
priority for the packets matching with the ACL rules.
Packet Filter Packet filter means filtering the service traffic. For example, in the operation of
dropping packets, the service traffic matching with the traffic classification rule is
dropped and the other traffic is permitted. The Ethernet switch adopts a complicated
traffic classification rule to filter the packets based on much information and to drop
these useless, unreliable, and doubtful packets. Therefore, the network security is
enhanced.
The two critical steps in the packet filter operation are:
1 Classify the inbound packets to the port by the set classification rule.
2 Perform the filter-drop operation on the classified packets.
The packet filter function can be implemented by applying ACL rules on the port.
Refer to the description in the
ACL module for detailed configurations.
TP and TS The network will be made more congested by plenty of continuous burst packets if
the traffic of each user is not limited. The traffic of each user must be limited in order
to make better use of the limited network resources and provide better service for
more users. For example, the traffic can only get its committed resources in an interval
to avoid network congestion caused by excess bursts.
TP (traffic policing) and TS (traffic shaping) is each a kind of traffic control policy to
limit the traffic and its resource usage by supervising the traffic specification. The
regulation policy is implemented according to the evaluation result on the premise of
knowing whether the traffic exceeds the specification when TP or TS is performed.
The token bucket is generally adopted in the evaluation of traffic specification.
Traffic evaluation and the token bucket
The token bucket can be considered as a container with a certain capacity to hold
tokens. The system puts tokens into the bucket at the set rate. When the token
bucket is full, the extra tokens will overflow and the number of tokens in the bucket
stops increasing.
3 011 excellent-effort
4 100 controlled-load
5 101 video
6 110 voice
7 111 network-management
Table 186 Description on 802.1p priority (Continued)
IP Precedence
(decimal) IP Precedence
(binary)
Description