07-13-2012 04:51 AM - edited 03-04-2019 04:57 PM
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.
Solved! Go to Solution.
07-13-2012 06:20 AM
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
07-13-2012 06:20 AM
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
07-13-2012 07:53 AM
Hello Peter,
Thanks for your answer.
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