Question on QoS

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 - 02:49:48 ART