Calculating virtual circuit oversubscription

Virtual circuits are oversubscribed when the sum of the virtual circuitlogical definitions that partition a a physical network circuit and used to determine what traffic passes through it and how much bandwidths exceeds the bandwidth of the parent circuit. For example:

Circuit Bandwidth = 3Mbps

  • Virtual Circuit Bandwidth A = 2Mbps
  • Virtual Circuit Bandwidth B = 1Mbps
  • Virtual Circuit Bandwidth C = 1Mbps

This means, the sum of the three virtual circuits is 4Mpbs, but the circuit bandwidth is only 3Mbps.

VC A: automatic

VC B: automatic

VC C: automatic

Each VC gets:

desired bandwith / sum of VC bandwith * circuit bandwidth

  • VC A = 2/4 * 3 = 1.5 Mbps
  • VC B = 1/4 * 3 = 0.75 Mbps
  • VC C = 1/4 * 3 = 0.75 Mbps

VC A: manual = 2 Mbps

VC B: manual = 0.5 Mbps

VC C: manual = 0.5 Mbps

Each virtual circuit with manually set oversubscription bandwidth will get their guaranteed amount

  • VC A = 2 Mbps
  • VC B = 0.5 Mbps
  • VC C = 0.5 Mbps

VC A: automatic

VC B: automatic

VC C: manual = 0.75 Mbps

Each virtual circuit with manually set oversubscription bandwidth will get their guaranteed amount. Virtual circuits with automatic oversubscription calculations will share the remaining bandwidth as:

virtual circuit's desired bandwidth / total remaining bandwidth * (circuit's bandwidth - sum of manually specified oversubscription bandwidths)

  • VC C = 0.75 Mbps
  • VC A = 2/3 * (3 - 0.75) = 1.5 Mbps
  • VC C = 1/3 * (3 - 0.75) = 0.75 Mbps

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