TEG1210P 10-Port Gigabit Intelligent PoE Switch User Guide
Chapter 4 Appendixes
4.1 Appendix 1: Glossary
¾
QoS
1 Overview of QoS
QoS(Quality of service) is the ability to provide better priority including improvement on a
required bit rate, jitter control and delay (for real-time and interactive flow), packet
dropping probability and specifying network flow for different WAN and LAN. In the
meantime, it guarantees that every flow with provided priority will not affect other flow’s
process.
QoS is a network security mechanism which is used to solve problems like network delay
and congestion, etc. In normal circumstances, if a network only works under specific
timeless application systems, then it does not need QoS, such as web application or
E-mail, etc. However, QoS technology is quite necessary for some key applications and
multimedia application. It guarantees that important data flows are not delayed or
discarded when network is overloaded or congested. Thus a highly efficient network is
guaranteed.
2. 802.1P Priority
802.1p priority that resides in layer-2 frame’s header adapts to the environment that
requires a guaranteed QoS in layer-2 environment instead of analysis of layer-3 frame
header. Only frames with 802.1Q tags have 802.1p priorities. The 4-byte 802.1Q tag
header consists of 2-byte TPID
（
Tag Protocol Identifier with a value of 0x8100
）
and 2-byte
TCI
（
Tag Control Information
）
as shown in the figure below.
Ethernet Frame with 802.1Q Tag header
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