ok no priority but how can i acheive the requirement? Using IPP will put traffic in the right Qs and it works but the client do not want to do any additional config on their equipment and am left by matching on VLANs.
Quite on the contrary, switch interfaces are always "congested", if by congestion we are talking about the interface is in "ON" state (sending a packet) and there are some packets that are in queue waiting for departure.
The more packets you have in queue, the more they have to wait. All queues are serviced using some round robins, and we don't want for a voice packet to wait it's turn to be sent or share the bandwidth for other flows for that matter. Just think of an almost 100 MB buffer on 6708 linecard. That's quite some wait time - about 80 miliseconds even on 10G interface.
So pripority queue is extremely important, because we don't want some packets to gain 80 ms delay on one node, when there are still 10 nodes to go in the way.
You can imagine it better if you imagine 3750-24TS with a SIP-400-type router attached via 2Gbps internal etherchannel to it.
So you need to do QoS on 3750 part and on ES part separately.
Because ES ports are connected via internal VLAN they can only match DSCP in the packet, or copy COS to EXP. No special mathes are allowed on ES ports, since packet never carries information on what VLAN it originated from, what port, etc.
If you'll do QoS for ES ports just like for the router, matching DSCP/EXP, IP information, etc, and do standard "mls qos" for the standard ports, it will all work.
Just remember, ES facility is very limited performance-wise since it's a software platform. So the more functions you type, the slower it'll become, just like 7201 router.
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