LLQ traffic behavior if no congestion

From: C Chan (cch.ccie@gmail.com)
Date: Sun May 04 2008 - 21:00:40 ART


Hi Expert,

Can anyone explain how to de-queue traffic assigned to LLQ if there is *no
congestion*? Normally, LLQ traffic use expedited queue to de-queue during
congestion. From Doc CD, the VOIP traffic is allowed to exceed 256kbps if no
congestion. But, will these traffic continue to use expedited queue to
de-queue? Or, it just performs de-queue with normal CBWFQ queues (eg HTTP,
SMTP) per round-robin basis according to allocated bandwidth ratio. If it
is true, low latency of exceed traffic is not guaranteed.

Where I can find cisco doc to discuss the detail of LLQ operation during *
non-congestion*?

*Quote from DocCD*
When the device is not congested, the priority class traffic is allowed to
exceed its allocated bandwidth.
When the device is congested, the priority class traffic above the allocated
bandwidth is discarded.

*Example*
interface BW: 1536k
!
policy-map FR_QOS
 class VOIP
  priority 256
 class HTTP
  bandwidth 512
 class SMTP
  bandwidth 256
!

Regards,
CH



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