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New Member

QoS Priority, Police, Shaping - Value Packets or Frame ?

Hello,

I have a question about the value to configure on Priority, Policing and Shaping.

Here an exemple of configuration:

policy-map COS-OUT

class DSCP-OUT-RT

  priority 920 115000

  police 928000 116000 116000 conform-action set-dscp-transmit ef exceed-action drop

Is that the values ​​are configured for Level 3 (Packets) or level 2 (Frame)?

For my example, we use ATM interface:

interface ATM0/1/0.1 point-to-point

description xxxxx

bandwidth 4608

I wanted to know if the mecanism of QoS took into account the overhead ATM?

I hope I was clear? :-)

Thanks for your answer.

1 ACCEPTED SOLUTION

Accepted Solutions
Cisco Employee

Re: QoS Priority, Police, Shaping - Value Packets or Frame ?

Hello Christopher,

Check this document:

http://www.cisco.com/en/US/tech/tk543/tk757/technologies_tech_note09186a0080103eae.shtml

It states, specifically: "With both commands [bandwidth and priority], the kbps value should take the Layer 2 overhead into account. In other words, if a guarantee is made to a class, that guarantee is with respect to Layer 2 throughput." That would mean to me that the Layer2 overhead is taken into account and thus deducts from the overall guarantee configured by bandwidth/priority commands.

Also, the following document states similar:

http://www.cisco.com/en/US/docs/ios/12_1t/12_1t3/feature/guide/dtcfgbst.html

It states: "Layer 2 encapsulations are accounted for in the amount of bandwidth specified with the priority command. However, the amount of bandwidth does not include other headers such as ATM cell tax overheads."

ATM in particular appears to require a slightly different take because of the additional ATM/AAL framing. See the following document for more information:

http://www.cisco.com/en/US/tech/tk39/tk824/technologies_tech_note09186a00800942f5.shtml

Best regards,

Peter

2 REPLIES
Cisco Employee

Re: QoS Priority, Police, Shaping - Value Packets or Frame ?

Hello Christopher,

Check this document:

http://www.cisco.com/en/US/tech/tk543/tk757/technologies_tech_note09186a0080103eae.shtml

It states, specifically: "With both commands [bandwidth and priority], the kbps value should take the Layer 2 overhead into account. In other words, if a guarantee is made to a class, that guarantee is with respect to Layer 2 throughput." That would mean to me that the Layer2 overhead is taken into account and thus deducts from the overall guarantee configured by bandwidth/priority commands.

Also, the following document states similar:

http://www.cisco.com/en/US/docs/ios/12_1t/12_1t3/feature/guide/dtcfgbst.html

It states: "Layer 2 encapsulations are accounted for in the amount of bandwidth specified with the priority command. However, the amount of bandwidth does not include other headers such as ATM cell tax overheads."

ATM in particular appears to require a slightly different take because of the additional ATM/AAL framing. See the following document for more information:

http://www.cisco.com/en/US/tech/tk39/tk824/technologies_tech_note09186a00800942f5.shtml

Best regards,

Peter

New Member

QoS Priority, Police, Shaping - Value Packets or Frame ?

Hello Peter,

Thanks for your answer.

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