LLQ and CBWFQ

Crunchyhippo

When would a person use LLQ instead of just CBWFQ? I'm having a bit of trouble distinguishing the two.

ITdude

Essentially when you want to add a priority queue to a certain class (in particular voice) to reduce things like jitter, you can assign them to a strict priority queue using LLQ.

You can think of LLQ as CBWFQ with the addition of a priority queue for real time traffic.

The higher priority classes are given low-latency propagation of packets and guaranteed bandwidth. If any congestion occurs within the higher priority classes, then they will be policed to prevent them from exceeding their bandwidth. All the lower priority classes will use CBWFQ.

This is obviously a very simplified explanation.

HTH

nice343

LLQ defines priority

CBWFQ defines bandwidth

LLQ is often used for voice traffic
CBWFQ is offten used for application like http

kryolla

The scheduler takes packets from LLQ first up to a max bandwidth where as the other ques are guarantee a minimum bandwidth and gets served after LLQ. Than it gets put in the transmit que which is FIFO. So if you have a class of traffic that is sensitive to delay and packet loss like voice traffic you would put that in low latency que.

networker050184

Just keep in mind that the priority que will only use the amount of bandwidth assigned and will not use any unused bandwidth from the other ques. In other words if you set the priority que for 56k thinking it will reserve 56k you are actually also limiting the priority que to that amount of bandwidth only.