A router has 2 types of queues:
- A hardware queue
- A software queue
The hardware queue , which is most of the time the transmit queues (TxQ) , uses FIFO queuing and it is only when the hardware queue is full that the software queue will handle these packets.
So remember that it is only valid when you are experiencing interface congestion (overflow of the hardware queue).
FIFO is also the default mechanism for software queue for higher speed interfaces ( > 2048 Mbps)
This queuing mechanism is the same as the Round Robin Queuing but this time ,we are placing a weight on the various queues which will service a different number of bytes or packets from the queues during a round robin cycle .
CQ ( Custom Queuing) is an example of Weighted Round Robin.
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)
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 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)
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