Hi,
Please have a look at each paragraph:
Committed Information Rate (CIR)
This is the rate (expressed in kbits/s) which is guaranteed that will always be available to the respective traffic class. Apparently, the CIF dedicated for a specific class, can not exceed the network bandwidth available. When multiple competing classes exist for the same interface and for the same direction (output/input), the sum of all of them should also not overrun the available bandwidth.
Note that, regardless of the CIR the traffic is always transmitted at the maximum speed supported by the physical interface. Literally, the CIR expresses the average rate in which the traffic is sent, in due time.
Peak Information Rate (PIR)
This is the maximum rate (in kbits/s) in which, the traffic of a class, can be sent or received (in average). Even if no other traffic competes for the bandwidth, this barrier can not be exceeded. This value can be as large as the capacity of the link and as small as the CIR.
The bandwidth between CIR and PIR is not guaranteed for a class. The possibility for a class to exploit this range, depends on its priority as we will see later.
Excess Burst Size (EBS)
Some applications are characterized by short periods of intensive network usage and long periods with no network usage at all. For instance, when we browse the Internet, our web browser requests a web page and then remains idle for a long period of time, until another page is requested. Such applications are not served well by the CIR/PIR mechanism alone. The EBS mechanism remedies this problem by allowing an application to send a number of bytes continuously, for some time, without being interrupted. As soon as EBC bytes have been sent, the application is forced back to normal behavior (average rate ranging between CIR and PIR).
Committed Burst Size (CBS)
The CBS corresponds to the minimum number of bytes that have to be available in order for a transmission to start. By the time that the transmission starts, it is not possible to be interrupted, until there are no other data to send. By default this value is the smallest possible (a single packet size ideally) and scarcely will you have to set a different value.
In order to better understand the concept of rate and burst, consider the analogy: Each class (or subclass as we will see later) is like a bucket with size EBS. The bucket is filled up at a rate which ranges between CIR and PIR. In accordance with this analogy, transmission starts when we throw water out of the bucket. The minimum quantity of water (traffic) that we can be thrown out is CBS. Therefore, when a class is idle for a while, it's possible for an application later on, to send a large burst of data, until the “bucket†is empty. Similarly, for a class that sends traffic at a steady rate, lower than CIR, its “bucket†will always be filled up
HTH
Mohamed
