Congestion Mgmt. - Queing Question

Deadmaster200Deadmaster200 Senior MemberMember Posts: 145
I just finished the Voice Transport chapter, and I have a question about the queing types.

Due to the small single-paragraph explanation, I can't see how WFQ and LLQ are different.
The book states

"WFQ recognizes IP precedence."

"CBWFQ provides WFQ based on defined classes, but no strict priority queue available for real-time traffic."

"LLQ adds strict priority queuing to CBWFQ."

Well, don't we already have this with WFQ and the IP precedence recognition?

I am sure there must be big differences, just this book does not go in such detail.

Please explain! (^_^)


  • Deadmaster200Deadmaster200 Senior Member Member Posts: 145
    Got no replies, but answered my own question after reading the end of Top Down Network Design. Thought I would share just in case any body was also wondering.

    First off, WFQ is not very configurable. It has uses an algorithm to adapt to changing network traffic conditions. It works with RSVP and Frame Relay congestion schemes (DE, FECN, BECN.

    CBWFQ. Highly configurable (complex config required). User defines traffic classes, then assigns things such as bandwidth and max number of packets that can be queued. This becomes the guaranteed bandwidth for the class during congestion.

    LLQ. Originally called PQ-CBWFQ, which really sheds light on the "LLQ adds strict priority queuing to CBWFQ." sentence. Basically, you get CBWFQ with ONE strict-priority queue, which Cisco recommends (strongly) that it be used only for voice traffic.

    Now that I have a better handle on it, bottom line is this:

    WFQ may recognize IP precedence, but it provides fair processing to all types of data (could be bad for voice/video). NOT CONFIGURABLE.

    CBWFQ - Configurable version of WFQ. (means still could be bad for voice/data)

    LLQ - CBWFQ plus one strict-priority queue making it voice's new best friend and Cisco quite the matchmaker!
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