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Controlling the Maximum Bandwidth of a Frame Relay Circuit

Article Number: T002
Article Type: Tip
Modified: January 22, 1999

SUMMARY

Managing bandwidth in a Frame Relay environment is often an important aspect of overall planning and network management. Since Frame Relay is by its very nature a "shared" medium, it is subject to abusers of bandwidth. The Orbitor can help you control this problem if you use its integral Frame Relay features effectively.

MORE INFORMATION

In most Frame Relay applications, many individual PVCs will share the same physical link into the Frame Relay network. And although there are "fairness" algorithms within the allocation of bandwidth between PVCs, limiting the maximum bandwidth that a single PVC may use can be an effective method of ensuring that bandwidth will always be available for the other PVCs on that link. The question then becomes, "How?"

The answer to this question is...

Excess Information Rate

Everyone has heard of Commited Information Rate (CIR). This is the rate of traffic that the PVC will support as "commited" traffic. Excess Information Rate (EIR) defines how much bandwidth in excess of CIR the PVC will be allowed to burst on a given PVC.

By default, the Orbitor sets EIR to the available link speed. This effectively means that each PVC will be able to burst up to the available link bandwidth. By limiting EIR to a lower value, the PVC becomes restricted to how much it can burst.

	Default: [link_speed]
	Range: 0 to 2048 Kb, "link_speed"

When EIR has been set to 0, this PVC is limited to the bandwidth specified by CIR only. As a result, this PVC is not allowed to burst beyond its defined CIR.

When EIR is a value larger than 0, the total bandwidth allowed by this PVC will be CIR + EIR. For example, if a PVC used a 32Kbps CIR and an EIR of 16Kbps, that PVC would be able to send 32Kbps of Commited traffic and 16Kbps of Excess traffic for a total of 48Kbps of traffic. Any traffic in excess of this total will be discarded, resulting in a real cap of the bandwidth used.

With EIR set to "link_speed" the only effective cap on this PVC is the total bandwidth availble on the link.

CONSIDERATIONS

Establishing a cap is not necessary, but it is prudent. Select an upper value that is appropriate for your application. Remember, a cap that is too low, may also cause application performance problems.

REFERENCES

Please consult the Orbitor Reference Manual for details regarding the use of these features.§

Copyright © 1999 Develcon Electronics Ltd.  All Rights Reserved.