I think all of us have experienced congestion management in our lives.
You get to the airport and you want to check in.
There's a queue or a line so you have to wait before your bags can be processed.
You get two security at the airport and you have to wait in a queue or a line you're driving on the
highway or motorway and lanes have been closed.
It results in congestion which results in a queuing mechanism being used to filter the traffic.
So queuing mechanisms manage congestion different queuing mechanisms can be used in the US as an example.
You have TSA pre check so that helps you get through security quicker.
If you've got a first class airplane ticket you're going to be processed quicker or better at check
in than if you've got an economy class ticket.
An ambulance will take priority on a motorway or a highway when there's congestion versus a standard
car.
So different queuing mechanisms can be used to determine how traffic is processed with round robin queuing
mechanisms.
All traffic is treated the same way.
That means that everyone is treated the same way that results in delay for real time traffic.
You could also implement a strict queuing mechanism where high priority traffic is always processed
first.
The advantage of that is voice packets will be transmitted first but if there is a lot of voice traffic
or high priority traffic it could result in starvation of less important traffic.
If you're constantly sending a lot of voice and video your FTE traffic may never be transmitted because
you are always transmitting video and voice first in a strict priority queuing mechanism.
So with congestion management we have queuing or buffering which determines the ordering of packets
in the output buffers.
In other words it determines how traffic leaves a road interface or leaves a switch interface.
You do have ingress queues but for now we'll just concentrate on egress queuing mechanisms queuing is
only required when there's congestion.
If you're driving on the highway or motorway late at night and there are six lanes and there are only
a few cars there's no need to have a queuing mechanism so queuing is used when there's congestion.
Hence the term congestion management when queues fill up packets are reordered so that high priority
packets are sent out of a rather interface first rather than lower priority packets.
So again when this congestion.
You may have high priority packets and low priority packets arriving a queuing mechanism is used to
determine which packets should be processed first and then they are scheduled for transmission out of
the interface of a rider.
So when packets arrive they're put into classes and will be processed on how important they are or based
on the queuing algorithm used.
More important packets will be transmitted first before less important traffic.
As an example so they will be scheduled for sending out of the interface of the router before less important
packets so queuing is the logic of ordering packets and output buffers scheduling is a process of deciding
which package should be sent out next.
Scheduling occurs regardless of whether there is congestion on the link queuing is only activated when
congestion occurs when queues fill up packets are reordered so that higher priority packets can be sent
out before lower priority packets.