Qos Mechanisms

>>Queuing Management (they appear when we encouter congestion in our network, so if our network doesn’t face congestion these queues aren’t use)

- Legacy Queuing methods

FIFO: First In First Out

Priority Queuing  : Here we have priority class organized from high priority to low priority,  the priority are dequeue until they become empty then we move to the next inferior queue, if after after dequeing  a queue , a queue with the more priority have packets we go to dequeue this queue.

Custom Queuing   : Like priority queuing but we have how many packet we have to dequeue from one queue before moving to the next inferior queue

Weighted Fair Queuing   : the router try to identify applications who use more bandwidth and those who use less, and try everytime to give access to the applications that use less bandwidth when these applications want to access the network

-Modern or new Queuing methods

CBWFQ = Custom Queuing + Weighted Fair Queuing (the unmanaged traffic often use WFQ)

LLQ = Priority Queuing + Custom Queuing + Weighted Fair Queuing (we have one and only one queue choose as a priority queue, this priority queue can have strict bandwidth limitation)

>>Congestion Avoidance (they appear before the congestion appear in our network)

WRED (Weighted Random Early Detection): Fight against TCP Synchronization
Drop packets before the congestion, as the router « think » that congestion may appear