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9.2 QoS
Tip
This section only applies to the switches G3310P-8-150W, G3318P-16-250W and G3326P-24-410W.
9.2.1 Overview
In traditional IP network, packets are treated equally. This network service policy is known as
Best-Effort, which delivers the packets to their destinations with the best effort, with no
assurance and guarantee for delivery delay, reliability, and so on. Nowadays, in addition to
traditional applications such as www, FTP and E-mail, new services occur, such as video
conference, remote education, Video-on-Demand (VoD) and video telephone, which need
higher requirements for bandwidth, delay and jitter. QoS (Quality of Service) policy can meet
the above demands and improve the quality of service in the network.
This switch classifies the messages according to priority at the ingress stage, then maps them
to different queues at the egress stage, and finally forwards these messages by queues
according to the scheduling mode, so as to guarantee the quality of network service.
Scheduling mode
This switch provides the simple QoS function. By setting a port priority, the system first
discards packets on low-priority ports during network congestion to ensure transmission of
packets on high-priority ports. The switch has a total of two priority queues. Queue Low is of
low priority. Queue High is of high priority. The scheduling algorithms supported by the switch
are First in First out (FIFO), Strict Priority (SP), and Weighted Round Robin (WRR). By default,
the scheduling algorithm is FIFO.
Queue scheduling algorithms
◼
First in First out (FIFO)
FIFO is that packets that are received first are forwarded first. It applies to most network
applications such as email and FTP.
◼
Strict Priority (SP)
Strict priority scheduling algorithm is specially designed for critical service applications. An
important feature of critical services is that they demand preferential service in congestion in
order to reduce the response delay.
In queue scheduling, the messages are sent in queues strictly following the priority order from
high to low. When the queue with higher priority is empty, messages in the queue with lower
priority are sent. You can put critical service messages into the queues with higher priority and
put non-critical service messages (such as E-mail) into the queues with lower priority. In this
Chapter 9 Device management 30