Adjustment Threshold; Overflow Detection - Cisco ASR 9000 Series Configuration Manual

Implementing MPLS Traffic Engineering
expires, and when the difference between the measured and the current bandwidth exceeds the adjustment
threshold, the tunnel is reoptimized. Then, the bandwidth samples are cleared to record the new largest output
rate at the next interval.
When reoptimizing the LSP with the new bandwidth, a new path request is generated. If the new bandwidth
is not available, the last good LSP continues to be used. This way, the network experiences no traffic
interruptions.
If minimum or maximum bandwidth values are configured for a tunnel, the bandwidth, which the automatic
bandwidth signals, stays within these values.
When more than 100 tunnels are auto-bw enabled, the algorithm will jitter the first application of every
Note
tunnel by a maximum of 20% (max 1hour). The algorithm does this to avoid too many tunnels running
auto bandwidth applications at the same time.
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 207
Configuring the Automatic Bandwidth Functions, on page 209
Configure Automatic Bandwidth: Example, on page 259

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.
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Cisco ASR 9000 Series Aggregation Services Router MPLS Configuration Guide, Release 4.3.x
MPLS-TE Automatic Bandwidth
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