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802.1Qtagged Ethernet frame
Below displays a detailed view of an 802.1Q tag. 802.1p priority, also known as class of service (CoS), is contained
in the priority field of the TCI. It is made up of 3 bits and with available values ranging from 0 to 7.
802.1QTag
The 802.1P priority tags are mapped to the Switch’s priority queues as follows:
802.1P priority
Queue
1, 2
1
0, 3
2
4, 5
3
6, 7
4
DSCP Priority
The DSCP priority resides in the IP header. The ToS field includes 8 bits, among which:
The first 3 bits denotes the IP priority, with available values ranging from 0 to 7.
Bits 3-6 denote the ToS priority, with available values ranging from 0 to 15.
The RFC 2474 redefined the IPv4 ToS field as the DS field. The DSCP priority is denoted by the first 6 bits (bits
0
～
5), with available values ranging from 0 to 63, while the last 2 bits (bits 6-7) are reserved.
The DSCP priority tags are mapped to the Switch’s CoS priority queues as follows:
DSCP Priority
CoS Priority
0~15
1
16~31
3
32~47
5
48~63
7
Scheduling Scheme Overview
QoS provides a queue scheduling policy to determine the packet forwarding sequence when congestion occurs. The
switch provides two common scheduling techniques to achieve Quality-of-Service (QoS) while using shared
resources: SP(Strict-Priority
）
and WRR (Weighted Round Robin).
Summary of Contents for G3224P
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