egress policing on SUP720 for sub-rate Metro-E link

Unanswered Question

we have a 500M Metro-E link terminated on the fiber 1G port on SUP720 itself (C6500). The switch sees the link as 1G instead of 500M.

The challenge is how to achieve QoS for VoIP traffic (dscp EF) without feature support of "shaping" on LAN ports. We don't have FlexWAN/SIP/SPA cards.

so I can't do:

1. shaping down to 500M

2. WRR since the port will never see egree queue filled up

Since DSCP marking is configured and we basically have two classes of traffics:

1. dscp 0 for data

2. dscp 46 for voice

I want your views on this "creative" QoS design in place of WRR queuing because the LAN port will never see the congestion at 500M.

Here is my plan:

1. implement egress policing on the LAN port connected to this 500M WAN link

2. police dscp 0 at 450M

3. implicitly IPT dscp 46/EF traffic can have 50M bandwidth when there is congestion on 500M WAN link

is it a valid design?

class-map match-all data

match ip dscp default

policy-map dropdata

class data

police 450000000 100000 100000 conform-action transmit exceed-action drop

int g5/1

desc 500M WAN link


service-policy output dropdata

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adamclarkuk_2 Wed, 03/25/2009 - 13:00
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I think it would make more sense to match the VoIP traffic and catch the rest in the class-default.

class-map VoIP

match ip dscp ef

policy-map dropdata

class Voip

police 50000000 conform-action transmit exceed-action drop

class class-default

police 450000000 conform-action transmit exceed-action drop

As this is Voip you my want to adjust the Time inteval by allocating a Bc value as you have done above, the 250ms default my affect your VoIP traffic during heavy usage (4ms being the smallest).

Just in case you didn't know the formula :-

CIR * / 8

So in your case for 0.004ms

50000000 * 0.004 / 8 = 25000 bytes

If you try to go down to 3ms for instance (18750), then it will adjust the value to the closest match which is 4ms.


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