Performance bounds for uncertain systems can be calculated by stochastic network calculus.In practice

interval mathematics can also deal with uncertainty.We construct the interval extension of wide-sense increasing functions

and study its properties by idempotent interval mathematics.For uncertain flows and servers

we can define arrival and service curve by convolution of function intervals

based on these two notions

we develop a new kind of network calculus which can be used to calculated performance bounds represented by intervals.Applications of interval network calculus are also given.