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Flow-Based Weighted Fair, Priority, And Custom Queueing
A Comparison of FBWFQ, PQ, and CQ
By Chris Bryant, CCIE #12933
Weighted Fair Queueing (Flow-Based)
No predefined limit on the number of queues
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Assigns weights to traffic flows
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Low-bandwidth, interactive transmissions are given priority over high-bandwidth transmissions
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The default queueing strategy for physical interfaces running at or less than E1 speed, AND that aren't running LAPB, SDLC, Tunnels, Loopbacks, Dialer Profiles, Bridges, Virtual Interfaces, or X.25.
Priority Queueing
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High priority queue traffic is always sent first, sometimes at the expense of lower queues whose traffic may receive inadequate attention
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Not the default under any circumstances, must be manually configured
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A maximum of 64 classes can be defined
Custom Queueing
17 overall predefined queues; Queue Zero is used for network control traffic and cannot be configured to carry other traffic, leaving 16 configurable queues
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Uses a round-robin transmission approach
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A maximum of 64 classes can be defined
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Not the default under any circumstances, must be manually configured
Deciding On A Queueing Strategy
The key to a successful queueing rollout is planning. Much like network design, there's no "one size fits all" solution for queueing. This is where your analytical skills come in. You're familiar with the phrase "measure twice, cut once"? You want to measure your queueing strategy at least twice before applying it on your network!
This decision often comes down to whether you've got voice traffic on your network. If you do, Priority Queueing is probably your best choice. PQ offers a queue (the High queue) that will always offer the highest priority to traffic - but you must be careful and not choke out traffic in the lower queues at the expense of priority traffic.
If there's no delay-sensitive traffic such as voice or video, Custom Queueing works well, since CQ allows you to configure the size of each queue as well as allocating the maximum amount of bandwidth each queue is allowed to use.
In comparison to PW and CQ, Weighted Fair Queueing requires no access-list configuration to determine priority traffic, because there isn't any priority traffic. Both low-volume, interactive traffic as well as higher-volume traffic such as file transfers gets a fair amount of bandwidth.
To your success,
Chris Bryant
CCIE #12933
chris@thebryantadvantage.com
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