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3750 qos - buffer size

Unanswered Question
Aug 14th, 2006
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I am putting together a VOIP qos config for a number of different switch types on of which is the 3750. We have a load of these switches an although the SRR method is different to me I think I have a handle on it.

The software config guides make numerous mention of configuring the queue sizes and weights etc in terms of buffer space percentage.

I believe that the amount of space available for egress and ingress buffers is fixed so I have a simple question.

What is the size of the total available buffer space either in bytes or number of packets ?

I cant find this anywhere. Seems to me that trying to allocate buffer space and weights without this info is more or less guessing.

I have the software config guide which is quite good but seems to leave out this kind of info, can anyone suggest a more complete document which may help ?

Many Thanks


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gpulos Mon, 08/14/2006 - 08:19
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two things...first things first:

1) see if AutoQoS (introduced in 12.2(15)T) will work for you to create a baseline QoS requirement...this may allieviate your need to crunch so many numbers/scenarios before you actually know what QoS your network requires.

2) the queues can be shared by percentage or shaped by bandwidth.

see the following links for 3750 QoS sharing & shaping:


see the following link for more info on 3750 QoS:



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