PLS inherits the merits of both topology driven and flow driven label distribution scheme.It can greatly improve the performance of router when label space is constrained.Some parameters

including scan window

damp factor

upper threshold and low threshold

are used in PLS.To achieve the best performance for router

the value of scan window should be sixty seconds.And the values of upper threshold and lower threshold should adapt to the size of label space and network traffic

which also are linear with the value of damp factor.