Avaya Configuring ATM and MPLS Services Instrukcja Użytkownika Pobierz pdf (Strona 55)

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Understanding ATM, MPOA, ATM Router Redundancy, and OAM

117374-C Rev 00

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Using the SCR

The SCR is the upper bound on the conforming average rate of an individual PVC

or control VC. The average rate is the number of cells transmitted over the link

divided by the duration of the connection. The duration of the connection is the

total amount of time it takes from connection setup to connection release.

The SCR allows you to define future cell flow on a PVC or control VC in greater

detail than by using only the PCR. The SCR controls the rate over time -- not at a

specific instant of time -- and can help you use your network resources more

efficiently. In other words, the SCR allows sufficient bandwidth for operation, but

does not allow a bandwidth as high as the PCR.

The SCR value maps directly to an MCR (minimum cell rate) value. In other

words, when you configure the SCR on a device, you actually configure the upper

bound of an average rate. Like the SCR, the MCR defines the minimum amount of

guaranteed bandwidth allowed for PVCs and control VCs on the ATM line. The

MCR (that is, SCR) not only controls the rate over time, it guarantees this rate.

When setting the SCR, keep the following considerations in mind:

• The SCR maps directly to the MCR.

• The MCR provides guaranteed bandwidth for PVCs and control VCs while

allowing sufficient bandwidth for SVCs to operate.

• To be useful, the SCR must not exceed the PCR.

• If you know the user average rate, set the SCR approximately 10 percent

higher than this value.

• ATM VCs may fail to operate with SCR values lower than 128 cells/s.

• Entering 0 for the SCR turns off this function and specifies that the ATM

router uses “best effort” for SCR.

• The E-3 framing mode setting affects the maximum SCR setting.

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