With the auto-bandwidth feature, the traffic rate through an LSP is sampled and the reserved bandwidth of the LSP is automatically changed through a make-before-break mechanism. This is done in order to keep the reserved bandwidth close to the actual traffic rate. It is beneficial to have an optimum bandwidth reservation for an LSP.
Several parameters are available to tune the automatic adjustment behavior. Some examples of parameters are the adjustment-interval, the sample-interval, the adjustment-threshold, and the overflow-limit. The basic auto-bandwidth functionality is that for every adjustment-interval, the predicted bandwidth is calculated as the maximum sampled traffic-rate in the previous adjustment-interval. For example, the adjustment interval is 10 minutes and the sample interval is 1 minute. Every adjustment-period contains 10 samples of traffic rate. Out of these 10 samples, the highest sampled rate is selected as the reserved bandwidth for the next adjustment interval.
Use the make-before-break procedure to change the bandwidth of an LSP without affecting the traffic. This procedure involves the exchange of RSVP control messages. The user may sometimes choose to ignore a bandwidth change when the difference in the current bandwidth and the predicted bandwidth is insignificant. For example, if the current bandwidth is 1 Mbps and the predicted bandwidth is 1.01 Mbps, the delta change is insignificant. To avoid a bandwidth adjustment, in this case, the user can set an adjustment-threshold. The user can configure the adjustment-threshold in terms of percentage in the previous releases. If the user sets the adjustment-threshold to be 10%, the bandwidth of an LSP adjusts only if the different between the current bandwidth and the predicted bandwidth is greater than 10% of the current bandwidth.
The actual traffic rate may not be close to the predicted rate always, given the very nature of prediction. In order to adapt to a higher traffic rate, it may be required to increase the reserved bandwidth of the LSP sooner than waiting for the adjustment-interval to expire. To achieve this, there is a parameter called the overflow-limit. If the overflow-limit is set to 3, and 3 consecutive samples of actual traffic-rate are found to exceed the current bandwidth by an amount greater than the configured threshold, a premature adjustment is triggered, setting the bandwidth to the maximum of the samples obtained so far in the adjustment-interval.
