Few questions regarding QOS

[ahmed.negm]

Hello All, I do really need a help on understanding some points on QOS. Given the below configuration

---------

R1#sh run policy-map COS-OUT-SHAPED-Gi0/0.15

Building configuration...

Current configuration : 124 bytes

!

policy-map COS-OUT-SHAPED-Gi0/0.15

class class-default

  shape average 6000000

  service-policy COS-OUT-Gi0/0.15

!

end

R1#sh run policy-map COS-OUT-Gi0/0.15

Building configuration...

Current configuration : 454 bytes

!

policy-map COS-OUT-Gi0/0.15

class DSCP-OUT-RT               <<<<<<<< Voice class

  priority 2448 307000

  police 2456000 307000 307000 conform-action set-dscp-transmit 46 exceed-action drop  violate-action drop

class DSCP-OUT-D1

  bandwidth remaining percent 60

     random-detect dscp-based aggregate

     random-detect exponential-weighting-constant 9

     random-detect dscp values 26 minimum-thresh 39 maximum-thresh 117 mark-prob 20

     random-detect dscp values 28 minimum-thresh 19 maximum-thresh 38 mark-prob 20

  service-policy COS-OUT-D1-Gi0/0.15   <<<< Those are just remarking service-policy so no big deal

class DSCP-OUT-D2

  bandwidth remaining percent 30

    random-detect dscp-based aggregate

    random-detect exponential-weighting-constant 9

    random-detect dscp values 18 minimum-thresh 61 maximum-thresh 122 mark-prob 20

    random-detect dscp values 20 minimum-thresh 34 maximum-thresh 68 mark-prob 20

  service-policy COS-OUT-D2-Gi0/0.15

class DSCP-OUT-D3

  bandwidth remaining percent 9

     random-detect dscp-based aggregate

     random-detect exponential-weighting-constant 9

     random-detect dscp values 10 minimum-thresh 78 maximum-thresh 156 mark-prob 20

     random-detect dscp values 12 minimum-thresh 51 maximum-thresh 102 mark-prob 20

  service-policy COS-OUT-D3-Gi0/0.15

!

end

-----------

Now my questions

1 - If customer is sending Data traffic with rate over 6 Mg will voice traffic be impacted or not ?

2 - Given the WRED parameters above or any other WRED just the concept , now if let's say D3 starts sending traffic with rate above 9 % of bandwidth Cisco allows it to be granted more bandwidth if there are available bandwidth in the other classes ... so my question is when will WRED mechanism gets triggered and starts dropping random packets ... or also in other words  minimum-thresh 78 .. The number 78 what's this number exactly a function of.

[JohnTylerPearce]

Joseph,

Thanks fo the reply, that makes complete sense. For instance, if I have 10 (10Mbps) ports, on Switch A, and

a one Gigabit Ethernet port going to Switch B as an uplink. No the output queue on this Gigabit Ethernet port

has only queue1, that has a queue_depth of 1. If they all send at the same time, it wil send one, and if it's running

FIFO will drop the rest. So from that ports point of view (The one Gigabit Ethernet) port, will show 10 percent

utilization. So if you're looking at the interface statistics, you thinking, man, that port isn't being hit that hard, which

is completely untrue, unless you look at the drops which should show.

I hope I got that right.

[Joseph W. Doherty]

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Posting

Thanks fo the reply, that makes complete sense. For instance, if I have 10 (10Mbps) ports, on Switch A, and
a one Gigabit Ethernet port going to Switch B as an uplink. No the output queue on this Gigabit Ethernet port
has only queue1, that has a queue_depth of 1. If they all send at the same time, it wil send one, and if it's running
FIFO will drop the rest. So from that ports point of view (The one Gigabit Ethernet) port, will show 10 percent
utilization. So if you're looking at the interface statistics, you thinking, man, that port isn't being hit that hard, which
is completely untrue, unless you look at the drops which should show.
I hope I got that right.

You got it exactly right!!!

Consider another situation.  You show 10% utilization and no drops in case where you have  a gig LAN interface which connects to a router with 1 Mbps WAN interface.  When you see 10% utilization (of the WAN interface) across, say, 5 minutes, is it 1 packet every 1/10 of 5 minutes, i.e. one packet every 30 seconds, or continuous packets (a microsburst), for 100,000 bits, at gig, that queue up and are transmitted for 30 seconds, and then no more for the remaining 4 minutes and 30 seconds?  So, with 10% utilization and no drops, again, everything is okay?

PS:

"There are lies, damned lies, and statistics." - Mark Twain

PPS:

Actually, statistics can be useful, if you really understand what they are telling you.