Can someone please explain those 2 concepts and rely them to marking, policing and shaping.
It is very confusing for me to rely these concepts with each other.
Fair Queuing share the link in equal capacity among the different flow.
Weighted Fair Queuing give allows schedulers to specify, for each flow, which fraction of the capacity will be given.
This prevent a single flow from using all the link bandwidth, effectively denying other flows.
But those mechanisms don't provide a priority system (I.E. which flow goes first).
Since some traffic (typically voice traffic) need priority, independently of link utilization,
Low-latency queuing (LLQ) extension to WFG was introduced by Cisco to provide this priority mechanism.
Quoted from Wikipedia:
LLQ allows delay-sensitive data (such as voice) to be given preferential treatment over other traffic by letting the data to be dequeued and sent first.