Brocade Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide (Supporting R05.6.00) - Manual (Page 64)

40 Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide
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Auto-bandwidth for RSVP LSPs
1
Configurable table-based absolute adjustment-threshold
The current percentage-based threshold configuration method has certain shortcoming when
there are LSPs with a very wide range of traffic-rates. Consider all the links from the ingress to be 1
Gbps links and the adjustment threshold to be 10%. Now, assume there are two LSPs A and B with
bandwidth 10 Mbps and 10 kbps respectively. The actual traffic-rate for LSP A is found to be 11
Mbps with an absolute difference of 1Mbps (1000kbps). The actual traffic rate for LSP B is found to
be 11kbps with an absolute difference of 1 kbps. Note that the percentage difference for both LSPs
is 10% and with the current method an adjustment event is triggered for both LSPs.
It may not be required to initiate a bandwidth adjustment for LSP B as the absolute difference is
very small as compared to the link bandwidth. You can have a higher threshold percentage for
LSPs with smaller current bandwidth and lower threshold percentage for LSPs with higher current
bandwidth.
One way to achieve such a threshold is to define a table which can give the absolute threshold
based on the current traffic rate. Following is an example of how a typical threshold table looks like.
An additional column is added for illustrating how the percentage threshold varies as the current
bandwidth increases.
Range of actual traffic rate Threshold Percentage threshold range
0-1000 kbps 2000 kbps ?? – 200%
1000 kbps to 10 Mbps 3000 kbps 300% - 30%
10 Mbps to 100 Mbps 5000 kbps 50% - 5%
100 Mbps to 1Gbps 7000kbps 7% - 0.7%
The absolute threshold values increase with the actual-traffic rate but the percentage threshold
decreases. This way you can make sure that for low traffic-rate LSPs, insignificant bandwidth
changes are ignored. This saves costly make-before-break procedures and thus provide an
scalability benefit over the current uniform percentage based method. This is particularly beneficial
in cases where a router is having LSPs with a wide range of actual-traffic rates.
Pros of the threshold-table based method:
• Useful when there are LSPs with wide range of actual traffic rate
• Huge scalability benefit. Avoid insignificant bandwidth adjustments
NOTE
It is important that the range of values and the corresponding thresholds are chosen very carefully.
The percentage-based threshold method and table-based threshold methods will co-exist. There is
another option to configure when an LSP is using the percentage-based threshold or the table
based threshold. There is a single global table only to be used system-wide by all LSPs. An LSP is
allowed to chose from either the threshold-table or the LSP level percentage threshold configured.
This flag behaves in the same way as the other LSP level auto-bandwidth parameters. This flag also
is allowed to be configured on an auto-bandwidth template. It follows the same inheritance
mechanism as other parameters. This threshold is valid for both overflow and underflow
determination.