Round Robin Queuing
This type of queuing places traffic into multiples queues and packets are removed from these queues in a round-robin fashion which avoids the protocol-starvation issue that PQ suffered from.(See PQ post)
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
CoS Switchport Queue Default Assignement
Here are the default CoS assignement for the queue unless you modify the standard
- CoS value 0,1 => Queue 1
- CoS value 2,3 => Queue 2
- CoS value 4,5 => Queue 3
- CoS value 6,7 => Queue 4
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