Re: Question on QoS

Hi Syed,

  The way in which I am understanding your scenarios are,the packets which
is marked with DSCP and packets non-marked with DSCP arrives ingress to an
interface.I am trying to understand your question,is your question ,what
would happen for the above mentioned packets at the ingress of the interface
?..If so,then I would assume the router would classify or take actions
appropriately based on the service-policy associated to the interface.

I would assume,by just having virtue of DSCP marking,the router wouldn't
classify it to a priority queue unless the service-policy actions specified
led to do so.So the router would base on the service-policy associated on
the ingress interface to take any action(like marking or classifying which
may eventually led to put in priority or non-priority queue on the egress
interface(again based on service-policy on the egress interface ....)

Kindly apologise if I didn't understood your question and responded
accordingly.Also will wait for the experts comments.

Thanks

Regards
Anantha Subramanian Natarajan

On Mon, Dec 7, 2009 at 3:49 PM, Syed Ali <testcricket_at_gmail.com> wrote:

> Hello All,
>
> What is the difference on the router in terms of ingress and egress
> classification between the following two scenarios , I say ingress and
> egress because for a traffic flow there is an ingress
> classification/queuing
> at the ingress point or port or module and their is an egress
> classification
> and queuing at the egress point or port or module, :
>
> 1) Router at the ingress interface receives IP packets already marked with
> DSCP.
>
> 2) Router at the ingress interface doesn't receive IP packets marked with
> DSCP. The router then is instructed to add DSCP value after the packet has
> been arrived at the ingress interface .
>
>
> From my knowledge the answers will be as follows:
>
> 1) In the first scenario, assuming that the router will not re-write the
> received DSCP value. Once a packet is received at the ingress interface
> marked with DSCP, at this moment the packet will be pushed to the
> *ingress*priority queue according to the DSCP value, later on the
> packet will be
> forwarded to the egress interface, it will be pushed to the
> *egress*priority queue according to the DSCP value set in the IP
> header.
>
> 2) In the second scenario, from my prospective the difference from
> scenario-1 is that when the packet received at the ingress interface
> without
> DSCP value marked, at the first place this packet will be placed into the
> default or low priority queue as any other packet not having the DSCP value
> set, then it will go to some processor and there as instructed a DSCP value
> will be added to that packet, after that it will be forwarded to the egress
> interface, the egress interface will push it into the priority queue
> according to the added DSCP value. In summary this scenario involves egress
> classification only which is different than ingress/egress classification
> described in point(1).
>
> Please clarify
>
> thanks
> Syed
>
>
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Received on Tue Dec 08 2009 - 15:02:23 ART