IP-COM F1226P - Page 41

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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 denotes 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.
DS-field and ToS byte
The 802.1P priority tags are mapped to the switch’s priority queues as follows:
DSCP Priority
Queue
0～15
1
16～31
2
32～47
3
48～63
4
3. 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).
Strict Priority Queuing