Understanding Qos Terminology
Tc -- Time interval, Tc=Bc/CIR
Bc -- Committed burst size, the bits can be sent per Tc interval. It specifies in bits (or bytes). Also called Sustained.
CIR -- Committed information rate, the bits can be sent per second. Also called Mean rate.
So Bc and CIR are same thing but measured in different way.
Be -- Excess burst size, bits can be sent per second beyond Bc after a period of inactivity.
Shaped rate -- bits per second, it may or may not be set to CIR.
At service provider side, CIR means the "guaranteed” rate of the circuit based on the SLA. At client side,
“CIR” in the context of shaping simply means the target average rate.
The actually speed of sending date can only be the line speed, to shape or policer the date to a lower speed, for example, to 10M of 100M Ethernet interface, the way the interface does is to send the data at line speed a very short period then stop, this send/stop is a interval called Tc, which can be 1/8 to 1/125 second. Shorter interval mean less delay for each packet. Tc can't be changed directly, so when CIR is specified, change Bc will change the Tc.
Bc -- Committed burst size, the bits can be sent per Tc interval. It specifies in bits (or bytes). Also called Sustained.
CIR -- Committed information rate, the bits can be sent per second. Also called Mean rate.
So Bc and CIR are same thing but measured in different way.
Be -- Excess burst size, bits can be sent per second beyond Bc after a period of inactivity.
Shaped rate -- bits per second, it may or may not be set to CIR.
At service provider side, CIR means the "guaranteed” rate of the circuit based on the SLA. At client side,
“CIR” in the context of shaping simply means the target average rate.
The actually speed of sending date can only be the line speed, to shape or policer the date to a lower speed, for example, to 10M of 100M Ethernet interface, the way the interface does is to send the data at line speed a very short period then stop, this send/stop is a interval called Tc, which can be 1/8 to 1/125 second. Shorter interval mean less delay for each packet. Tc can't be changed directly, so when CIR is specified, change Bc will change the Tc.
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