Priority Queuing

This type of queuing places traffic into one of four queues. Each queue has a different level of priority and higher priority queues must be emptied before packets are emptied from lower priority queues.

This behaviour can “starve out” lower priority traffic

FIFO Queuing

FIFO stands for First In First Out .

So you can easily understand the meaning of this queuing mechanism : The first packet in the queue is the fisrt packet which will be sent out of the queue.

FIFO is also the default mechanism for software queue for higher speed interfaces ( > 2048 Mbps)

General Queuing Definition

Queuing issometimes reerredto as congestion management as it identifies how trafic from multiple streams is sent out of an interface which is currentlyexperiencing congestion.

In other words, the queuing is the fact that a device( router or switch) will attempt to bufferize the extra traffic until the bandwidth will be available again

Switch Default CoS-to-DSCP and DSCP-to-CoS Mappings

Here are the default values for the mapping until you decide to change it

First let’s see the CoS-to-DSCP mapping

  • CoS 0 => DSCP 0
  • CoS 1 => DSCP 8
  • CoS 2 => DSCP 16
  • CoS 3 => DSCP 24
  • CoS 4 => DSCP 32
  • CoS 5 => DSCP 40
  • CoS 6 => DSCP 48
  • CoS 7 => DSCP 56

After let see the reverse side with the DSCP-to-CoS mapping

  • DSCP 0 => CoS 0
  • DSCP 8,10 => CoS 1
  • DSCP 16,18 => CoS 2
  • DSCP 24,26 => CoS 3
  • DSCP 32,34 => CoS 4
  • DSCP 40,46 => CoS 5
  • DSCP 48 => CoS 6
  • DSCP 56 => CoS 7
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