MPLS Traffic Engineering

A pipe/path/circuit that has a defined bandwidth (e.g., a “Cat-5” cable) can in theory process 100 Mb/s, while an OC-12 can process 622 Mb/s.  These are bits crossing the pipe and comprise all overhead and payload bits.

In order to determine the data throughput at any given stage, you can measure the data traveling through a pipe with relative accuracy by using networking-measurement tools.  Using an alternate measurement method, you can calculate necessary bandwidth by calculating the total payload bits per second and adding the overhead bits per second; this second method is more difficult to calculate and less accurate than actually measuring the pipe.

If the OC-12, which is designed to handle 622 Mb/s, is fully provisioned and the traffic placed on the circuit is less than 622 Mb/s, it is said to be over-provisioned. By over-provisioning a circuit, true Quality of Service (QoS) has a better chance of becoming a reality; however, the cost per performance is significantly higher.

If the traffic that is placed on the OC-12 is greater than 622 Mb/s, then it is said to be under-provisioned.  For example, commercial airlines under-provision as a matter of course, because they calculate that 10-15% of their customers will not show up for a flight. By under-provisioning, the airlines are assured of full flights; but they run into problems when all the booked passengers show up for a flight.  The same is true for network engineering – if a path is under-provisioned, then there is a probability that there will be a problem of too much traffic.  The advantage of under-provisioning is a significant cost savings; the disadvantages are loss of QoS and reliability.

Figure 5-3:  Over-Provisioning v. Under-Provisioning

In figure 5-3, you can see that you can over- or under-provision a circuit in percentages related to the designed bandwidth.

Figure 5-4: Comparison of Over Provisioning and Under Provisioning

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