Automatic bandwidth allocation is supported on any RSVP LSP that has MBB enabled. MBB is enabled in the config>router>mpls>lsp context using the adaptive command. If the monitor-bandwidth command is enabled in config>router>mpls>lsp>auto-bandwidth context, the LSP is not resignaled to adjust its bandwidth to the calculated values.
If an eligible RSVP LSP is configured for auto-bandwidth, by entering auto-bandwidth at the config>router>mpls>lsp context, then the ingress LER decides every adjust interval whether to attempt auto-bandwidth adjustment. The following parameters are defined:
current_bw — The currently reserved bandwidth of the LSP; this is the operational bandwidth that is already maintained in the MIB.
measured_bw — The maximum average data rate in the current adjust interval.
signaled_bw — The bandwidth that is provided to the CSPF algorithm and signaled in the SENDER_TSPEC and FLOWSPEC objects when an auto-bandwidth adjustment is attempted.
min — The configured min-bandwidth of the LSP.
max — The configured max-bandwidth of the LSP.
up% — The minimum difference between measured_bw and current_bw, expressed as a percentage of current_bw, for increasing the bandwidth of the LSP.
up — The minimum difference between measured_bw and current_bw, expressed as an absolute bandwidth relative to current_bw, for increasing the bandwidth of the LSP. This is an optional parameter; if not defined the value is 0.
down% — The minimum difference between current_bw and measured_bw, expressed as a percentage of current_bw, for decreasing the bandwidth of the LSP.
down — The minimum difference between current_bw and measured_bw, expressed as an absolute bandwidth relative to current_bw, for decreasing the bandwidth of the LSP. This is an optional parameter; if not defined the value is 0.
At the end of every adjust interval the system decides if an auto-bandwidth adjustment should be attempted. The heuristics are as follows:
If the measured bandwidth exceeds the current bandwidth by more than the percentage threshold and also by more than the absolute threshold then the bandwidth is re-signaled to the measured bandwidth (subject to min and max constraints).
If the measured bandwidth is less than the current bandwidth by more than the percentage threshold and also by more than the absolute threshold then the bandwidth is re-signaled to the measured bandwidth (subject to min and max constraints).
If the current bandwidth is greater than the max bandwidth then the LSP bandwidth is re-signaled to max bandwidth, even if the thresholds have not been triggered.
If the current bandwidth is less than the min bandwidth then the LSP bandwidth is re-signaled to min bandwidth, even if the thresholds have not been triggered.
Changes to min-bandwidth, max-bandwidth and any of the threshold values (up, up%, down, down%) are permitted at any time on an operational LSP but the changes have no effect until the next auto-bandwidth trigger (for example, adjust interval expiry).
If the measured bandwidth exceeds the current bandwidth by more than the percentage threshold and also by more than the absolute threshold then the bandwidth is re-signaled to the measured bandwidth (subject to min and max constraints).
The adjust-interval and maximum average data rate are reset whether the adjustment succeeds or fails. If the bandwidth adjustment fails (for example, CSPF cannot find a path) then the existing LSP is maintained with its existing bandwidth reservation. The system does not retry the bandwidth adjustment (for example, per the configuration of the LSP retry-timer and retry-limit).