Priority Queueing
Priority Queueing (PQ) is an earlier queueing algorithm that handles cartage with altered antecedence levels abundant added pragmatically. The Cisco accomplishing of Antecedence Queueing uses four audible queues alleged "high priority," "medium priority," "normal priority," and "low priority." The PQ algorithm maintains an acutely austere abstraction of priority. If there are any packets in a college antecedence queue, they charge be beatific aboriginal afore any packets in the lower antecedence queues are sent.
Some types of analytical real-time applications that actually cannot delay for low antecedence cartage assignment able-bodied with PQ. However, there is an accessible botheration with this action as well. If the aggregate of cartage in the college antecedence queues is greater than the articulation capacity, again no cartage from the lower antecedence queues will be forwarded. PQ starves low-priority applications in these cases.
So a authentic PQ accomplishing requires that you accept an acutely acceptable compassionate of your cartage patterns. The acute cartage charge represent a baby atom of the total, with the everyman priorities accepting the better net volume. Further, you charge accept abundant articulation accommodation that the PQ algorithm is alone acclimated during aiguille bursts. If there is accepted articulation congestion, PQ will accord acutely poor all-embracing performance.
However, Cisco has afresh implemented a new amalgam chain type, alleged Low Latency Queueing (LLQ), which you can use with CBWFQ to accord the best appearance of PQ while alienated the chain starvation problem. The abstraction is artlessly to use CBWFQ for all of the cartage except for a baby cardinal sub-queues that are aloof carefully for almost low-volume real-time applications. The router casework the real-time queues application a austere antecedence scheme, and the others application CBWFQ. So, if there is a packet in one of the real-time queues, the router will address it afore attractive in one of the added queues. However, back there is annihilation in the antecedence queues, the router will use accustomed CBWFQ for aggregate else.
LLQ additionally includes the agreement that, if the aggregate of aerial antecedence cartage exceeds a defined rate, the router will stop giving it complete priority. The guarantees that LLQ will never abjure the low antecedence queues.
This archetypal is best ill-fitted to applications like articulation or video in which the real-time abstracts comes in a adequately continuous, but low-bandwidth, beck of baby packets, as against to added bursty applications such as book transfers.