qos - How traffic congestion happens?

[krish1986]

Hi all,

We can do policing/shaping at ingress traffic. If the traffic is already rate limited/shaped at ingress, then what’s the use of WRED-Weighted random early detection? How the congestion can happen, because already the traffic flow is policed. Per flow, 1 queue also will be there. Then what may be the reason for congestion?

 Thank you,

[M02@rt37 · Accepted solution]

 Hi @krish1986

Differents reasons cause congestion...see the gif attached.

All the mechanisms you have configured will be triggered if congestion exist.

You have got on one side congestion avoidance like WRED - RED - ERED.

Traffic shapping and policing are aslo QOS mechanisms for congestion avoidance. They limit the bandwidth of certain network traffic (drop or queues exess traffic).

And you have got also all queuing and congestion management/ algorithm like LLQ - CBWFQ - WFQ.

The mechanism algorithm you will configure depend of what is or what should be your problem,i.e. lake of bandwitdh, packets loss, delay etc...

All the mechanisms you have configured will be triggered if congestion exist.