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Using Packet Prioritization on a Traffic Shaping Rule

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Traffic priority is a way of ensuring that specific applications or subnets are guaranteed a certain amount of the uplink bandwidth at all times. Traffic priorities only come into play when the network is using all of the pre-configured bandwidth on the uplink. Take note that this bandwidth can change when link aggregation is enabled because the uplink changes per stream based upon the ratio specified.  

Specifying a traffic shaping rule as High, Normal, Low guarantees a certain fraction of the uplink to each priority level. The ratios are as follows:

  • High       4/7
  • Normal   2/7
  • Low       1/7

 

By default all traffic is marked as having a Normal priority level. Traffic shaping rules that are marked at the same priority level share the same fraction of their respective levels. For instance if there are 5 traffic shaping rules marked as High priority on a 10Mbps pipe each rule would have access to ~1.1Mbps.

 

Each traffic rule supersedes each rule below it and the rules below it must strictly adhere to their fractional bandwidth limits. For instance if there is a high traffic shaping rule but no low traffic shaping rules configured then the the high priority traffic would have access to 5/7 of the available bandwidth on the uplink and normal traffic would have 2/7s. Additionally if there are no high priority traffic shaping rules then normal priority traffic gets 6/7 of the bandwidth and low priority gets 1/7 of the uplink's bandwidth.

 

Here are some examples on a 7 Mbps Up link:

 

Case 1:

With 2 high priority rules each get 2Mbps for a total of 4Mbps

With 2 normal priority rules each get 1Mbps for a total of 2Mbps

With 2 low priority rules each get .5Mbps for a total of 1 Mbps

 

Case 2:

With 2 high priority rules each get 2Mbps for a total of 4Mbps

With 1 normal priority rule it gets 2Mbps for a total of 2Mbps

With 10 low priority rules each get .1Mbps for a total of 1 Mbps

 

Case 3:

With 2 high priority rules each get 3Mbps for a total of 6Mbps

With no normal priority rules there is a total of 0Mbps

With 5 low priority rules each get .2Mbps for a total of 1 Mbps

 

Case 4:

With 5 high priority rules each get 1Mbps for a total of 5Mbps

With 4 normal priority rules each get .5Mbps for a total of 2Mbps

With no low priority rules there is a total of 0Mbps

 

Case 5:

With no high priority rules there is a total of 0Mbps

With 3 normal priority rules each get 2Mbps for a total of 6Mbps

With 2 low priority rules each get .5Mbps for a total of 1Mbps

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Last modified
08:29, 19 May 2015

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ID: 1376

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