ATM PVC bandwidth design

Unanswered Question
Jun 16th, 2008

I have an ATM network based on LS1010switches and 7206 routers. The interface speed is usually 155Mbps and normally has several PVC's configured across each interface. My question is how do I decide what bandwidth figures I give to each PVC (sustained, peak, burst rates) and what are the limits for each one? I understand the config steps but I am having trouble finding a guide to what the values should be.

I have this problem too.
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nnandrek Mon, 06/16/2008 - 05:41


That should depend on what min bandwidth you are expecting that the VC should get in cases of congestion. So the values are totally driven by requirement.

In cases where there is no congestion, the VCs will anyways use all the bandwidth available. Whenever you have multiple VCs configured, and you want to assure min. bandwidth to certain VCs in case of congestion, configure the required bandwidth.

The sustained rate is the actual rate which will be assured, while the peak rate is the rate till which the traffic will be allowed to reach in case the bandwidth is accumulated in previous time cycle. The burst size is the max burst it can send in one cycle and you can let the config take the default burst size.



tomredmond Mon, 06/16/2008 - 06:39

Thanks for your reply, I hope I understand you correctly, if I look at traffic stats, decide the minimum bandwidth needed for a link, assign that as the SCR for the PVC, making sure that the total SCR's for an interface don't exceed the available bandwidth, that the peak rate for a PVC is less than the available bandwidth and finally leave the max burst size blank then I should be OK?

Is the available bandwidth the link bandwidth or a percentage of it?

Paolo Bevilacqua Mon, 06/16/2008 - 06:29

Hi, how is you trunking between LS1010s done ?

If OC12 or faster you can simply configure routers for UBR at full OC3 speed, over all the PVCs, then as you find out if any trunk or user interface gets congested, start modifying BW allocation to routers.

If you do hard policing on the PVC the net effect is that routers will never transmit faster than SCR over time and this can be a performance limitation not needed for when you've a lot of BW on trunks.


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