If a tunnel is shut down, and is later brought again, the adjusted bandwidth is lost and the tunnel is brought
back with the initial configured bandwidth. In addition, the application period is reset when the tunnel is
brought back.
Related Topics
Configuring the Collection Frequency, on page 288
Configuring the Automatic Bandwidth Functions, on page 291
Configure Automatic Bandwidth: Example, on page 353
Adjustment Threshold
Adjustment Threshold
is defined as a percentage of the current tunnel bandwidth and an absolute (minimum)
bandwidth. Both thresholds must be fulfilled for the automatic bandwidth to resignal the tunnel. The tunnel
bandwidth is resized only if the difference between the largest sample output rate and the current tunnel
bandwidth is larger than the adjustment thresholds.
For example, assume that the automatic bandwidth is enabled on a tunnel in which the highest observed
bandwidth B is 30 Mbps. Also, assume that the tunnel was initially configured for 45 Mbps. Therefore, the
difference is 15 mbit/s. Now, assuming the default adjustment thresholds of 10% and 10kbps, the tunnel is
signalled with 30 Mbps when the application timer expires. This is because 10% of 45Mbit/s is 4.5 Mbit/s,
which is smaller than 15 Mbit/s. The absolute threshold, which by default is 10kbps, is also crossed.
Overflow Detection
Overflow detection is used if a bandwidth must be resized as soon as an overflow condition is detected, without
having to wait for the expiry of an automatic bandwidth application frequency interval.
For overflow detection one configures a limit N, a percentage threshold Y% and optionally, a minimum
bandwidth threshold Z. The percentage threshold is defined as the percentage of the actual signalled tunnel
bandwidth. When the difference between the measured bandwidth and the actual bandwidth are both larger
than Y% and Z threshold, for N consecutive times, then the system triggers an overflow detection.
The bandwidth adjustment by the overflow detection is triggered only by an increase of traffic volume through
the tunnel, and not by a decrease in the traffic volume. When you trigger an overflow detection, the automatic
bandwidth application interval is reset.
By default, the overflow detection is disabled and needs to be manually configured.
Underflow Detection
Underflow detection is used when the bandwidth on a tunnel drops significantly, which is similar to overflow
but in reverse.
Underflow detection applies the highest bandwidth value from the samples which triggered the underflow.
For example, if you have an underflow limit of three, and the following samples trigger the underflow for 10
kbps, 20 kbps, and 15 kbps, then, 20 kbps is applied.
Unlike overflow, the underflow count is not reset across an application period. For example, with an underflow
limit of three, you can have the first two samples taken at the end of an application period and then the
underflow gets triggered by the first sample of the next application period.
Cisco IOS XR MPLS Configuration Guide for the Cisco CRS Router, Release 5.1.x
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Implementing MPLS Traffic Engineering
MPLS-TE Automatic Bandwidth
