Re: use of CS in qos?

I think you are misunderstanding Abderrahim. The bits are exactly the same,
it is just a matter of what you call them. A device that only looks at IPP
will look at the 3 most significant bits in the ToS field of the IP header.
DSCP CS values use the 6 most significant bits of the same field, but only
the 3 most significant bits really matter in CS since the lower 3 bits of
every CS will always be 0.

So check it out for example:

[ToS Field]

       ^
001 00000 = IPP 1 = CS1

It's all the same thing.

On Fri, Jul 3, 2009 at 6:18 PM, abderrahim sadki <a_sadki1_at_hotmail.com>wrote:

> thanks for your answer.
>
> but i was wondering does a device (understading only IPP) gets a DSCP
> marking isnt it going to ignore the last 3 bits anyway?
> if yes what the point of the CS?
>
> Abderrahim
>
> ------------------------------
> Date: Fri, 3 Jul 2009 18:12:33 -0400
> Subject: Re: use of CS in qos?
> From: jastorino_at_ipexpert.com
> To: a_sadki1_at_hotmail.com
> CC: ccielab_at_groupstudy.com
>
>
> Hey,
>
> IPP uses the most significant 3 bits in the ToS field in the IP
> header. With DSCP the CS values essentially do the same thing. In order
to
> be backwards compatible with IPP it only uses the 3 most significant bits.
> Maybe this will help you visualize:
>
> CSx Dec. IPP Binary
>
> CS1 8 1 001 000
> CS2 16 2 010 000
> CS3 24 3 011 000
> CS4 32 4 100 000
> CS5 40 5 101 000
> CS6 48 6 110 000
> CS7 56 7 111 000
>
> HTH
>
> On Fri, Jul 3, 2009 at 5:04 PM, abderrahim sadki
<a_sadki1_at_hotmail.com>wrote:
>
> Hi all.
>
> I understand that CS is used for backward compatibility with IP precedence.
>
> My question is :
> if a device only understands the IP precedence and it receives a packet
> with
> the dscp marking isnt it going to ignore the last 3 bits anyway?
>
> Thanks,
> Abderrahim
>
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