This sets the loss level at which this device will declare a signal-degrade condition for this synthetic-loss session, a softer, earlier warning than a hard fault meant to catch a service that is degrading but not yet fully failing. Per the description, a value of -1 disables this signal-degrade detection entirely, while any value 0 or higher is compared against the measured loss result to decide when to raise that degrade condition, and the description notes this threshold is meant to be configured together with the corresponding clear-threshold below it rather than in isolation.