Hi Ivan, Comments within lines
>From: "Ivan Yip" >Hi All, >I am a little bit confused about LLQ. Below is my understanding after >digesting some documentation and feedback from others. Please correct me if >I'm wrong. >1. LLQ=PQ+CBWFQ and PQ is defined by using 'priority' You are correct. >2. if using 'bandwidth', then I'm not using LLQ. What I'm using is CBWFQ. You are only allowed to use the priority keyword with the PQ where its main concern is to forward packets as fast as it can. That's why no queue size is configured for it. As your main concern is latency so once the defined bandwidth you assigned for the PQ using the priority keyword is reached the PQ will start dropping immediately. The point here is: Dropping a voice packet is better than delivering it delayed - from the voice quality prespective - You start using the "bandwidth" keyword with the rest of the classes defined to indicate the usage of CBWFQ. Also you will need to use WRED in order to define min_threshold, max_threshold, and how fast you drop from each class via the exponentianl value defined. >3. PQ (from LLQ) defines the min. and max. guaranteed bandwidth to >the traffic I defined during congestion. > Not necessary during congestion. PQ is treated separetly from the CBWFQ to gurantee low latency for this type of traffic even in normal situations. Imagine a voice packet waiting for a long data packet to be transmitted. This will make the voice packet delayed - i.e. degradation in voice quality which we don't want to happen - this will lead to the fact that you will need to configure LFI to avoid long data packets delaying your voice. >Also, do I need to define the class-default under policy? > >eg,policy-map 1 > class 1 > priority 80 > class class-default > fair-queue > >What's the difference if I'm not defining the class-default? Yes you need doing so. But when you do so you will also define the min_threshold, max_threshold of this class default. After all traffic classified in default class is not sentitive at all for delay and more packets could be kept in its queue without a noticable degradation in performance. For example: Policy-map out class A Bandwidth percent 50 random-detect random-detect exponential-weighting-constant 3 random-detect precedence 3 2 5 1 class class-default fair-queue random-detect random-detect exponential-weighting-constant 2 random-detect precedence 0 6 18 1 Yasser misconduct and Nondisclosure violations to [EMAIL PROTECTED] ------------------------------------------------------------------------ 3 months FREE*. Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=59952&t=59820 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
