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Community Member

T1 Frame Relay how many PVC's w/28k CIR

T1 will support multiple subinterfaces on our Cisco 7200 Router. We have a hub and spoke topology with 56 circuits at the edge with a CIR of 28k. How many possible number of subinterfaces can I have or what is the formula for figuring this out? I would like to determine the amount possible with a single T1 and multiple remote 56k edge devices. The pvc is built with a cir of 28k. Thanks in advance for helping out!!

Hall of Fame Super Bronze

Re: T1 Frame Relay how many PVC's w/28k CIR

The limit is usually imposed by the telco since they provide the SLAs (Service Level Agreement).

Do your own math, the hub is a T1 = 1544kbps - divide that for the number of remote connections you are planning to host. Do your math based on the worse case scenario.

Community Member

Re: T1 Frame Relay how many PVC's w/28k CIR

Is there a link/PDF that shows how this is divided out? My concern, we are currently in a state where we have over 100 PVC's per T1. We plan to change our source - destination transmit method from X25 to IP. This will cause us to see much more traffic utilized then the 9.6 kbps that we are used to seeing. Or will the impact of this change not be significant. Just planning ahead.


Hall of Fame Super Gold

Re: T1 Frame Relay how many PVC's w/28k CIR


to add to the good advice given by Edison, if you are currently still using X.25, the router will be very very relieved migrating to FR, even if the bandwidth per spoke is more than doubled.

100 PVCs per interface is not really a big number per se. However, with 28 Kbps CIR per branch on a T1, you will be oversubscribing the sum of CIR: 28,000 x 100 = 2,800,000 that exceed the 1,544,000 capacity of a T1.

This means that to all effects, you will be never be able to transmit at maximum rate to all branches simultaneously.

Understand that is not a problem for "ticket like" applications, where the transactions are small and well spread over time. I did many projects for this industry, and still doing :)

hope this helps, please rate post if it does!

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