QoS : Difference between AIR and CIR ...

Unanswered Question
Jul 2nd, 2007


What is the difference between Access Information Rate and Committed Information Rate ? Is it that AIR is the total bandwidth on the link and CIR is the committed bandwidth to be used for a specified used defined in QoS ?

Pls advice,

Thank you,


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Edison Ortiz Tue, 07/03/2007 - 05:14

The Access-Rate is often referred to the maximum bandwidth allocated to a port. The Committed rate is the guaranteed bandwidth when there is congestion in the line.

Pavel Bykov Tue, 07/03/2007 - 06:09

Let's say you have Fast Ethernet cable from an ISP, that provides you with 5Mbps internet.

AIR in this case is 100 Mbps, because that's media standard, and data CANNOT be sent at any other rate.

CIR on the other had is controlled by provider using policing, shaping or other tools, to limit data to 5 Mbps.

Or for example if you have unstructured E1 link from the provider that allows you to use 512Kbps over Frame relay.

AIR is always 2048, since that's defined by E1 standard and serial connection can only send data at that speed.

CIR is 512Kbps, and is done by using shaping (in case of frame relay probably FRTS) or policing or other methods.

Pavel Bykov Tue, 07/03/2007 - 06:09

Basically, AIR is specification of the media. And CIR is bandwidth you actually get.


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