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User Manual
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27
5
QoS
5.1
QoS Classification
QoS(Quality of Service) is used to assess service provider’s ability in meeting client
service demands. As for network business, service quality includes transmission
bandwidth, transfer delay, data packet loss rate and so on.
The service quality issues that traditional network faces are caused by network
congestion. The so-called congestion refers to the phenomenon that the forwarding
rate decreases and extra delays are introduced caused by the relative shortage of
supply resources, thus leading to the decline of service quality. As for congestion
management, queue technology is generally adopted. It uses a queue algorithm to
classify flow, then uses some priority algorithm to send these flow.
Priority is used to tag the priority of message transmission.
CoS
Ethernet has defined 8 service priorities (CoS, Class of Service) in the VLAN TAG
of Ethernet frame header. The 802.1Q label head of 4 bytes has included 2-byte
TPID
(
Tag Protocol Identifier) and 2-byte TCI
(
Tag Control Information), TPID’s is
0x8100, the following graph has displayed the details of 802.1Q label head,
priority field is 802.1p priority.