what is the difference between layer 2 and layer 3 qos

Answer Posted / trilokchand kilari

Well, none of the above answers talk about QOS,

L2-QOS:
-------
It is clear that L2 is at MAC layer. In case of MAC level
forwarding such as Bridge connction and a quality of
service need to be assured, The following methods can be
used:

1) MAC filtering (avoiding unnecessary traffic coming from
known MAC sources)
2) VLAN & COS: VLAN will ensure that the traffic is
classified based on various parameters like MAC address,
incoming port, etc... COS: Class Of Service is a filed in
VLAN header. This will be used to prioritize traffic. Later
a QOS scheduler can use the COS filed to qualify the
traffic in to different QOS queues.

L3 - QOS
--------

L3 QOS is required for IP level classification.
Classification can be achieved by Diffserv implementations
that takes many IP parameters in to consideration in
prioritizing traffic. This priority can be set in TOS field
of IP header. This TOS will later be used by Scheduling
process to achieve QOS.

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