Question

Is it acceptable to allow thresholds to be configured in SLA?

Solution

Yes, it is acceptable to configure thresholds.

If thresholds are configured, then paths are put into priority buckets based on whether they meet the SLA or not. 

Example:

Consider 3 links L1, L2, and L3 configured as priority 1, with only L1 and L2 meeting the SLA of 10% forward loss.

Then L1 and L2 will be at priority 1, and L3 will be at SLA-violated priority.

A path from the highest priority bucket is always selected first. In this case, selection is between L1 and L2. 

If  low loss is also configured, then among the eligible circuits L1 and L2, the one with the least loss is selected.