## sbws: design and construct bias curves

From https://trac.torproject.org/projects/tor/ticket/25687#comment:13

The essence of Torflow's active approach is that observed bandwidth capacity at each relay is the key measurement and that it can only be reliably determined locally but that it requires adjustment, principally to account for used vs unused capacity and secondly the relative performance of each node in the asymmetric domain of internet traffic routing. IMO indisputably correct. The Peerflow paper tacitly recognizes this.

However the simple linear adjustment algorithm cannot be fine-tuned for better results across the vast range of relay performance. IIRC polynomial equations of sufficient order can describe curves of near arbitrary complexity and therefore parameterized polynomials can be used interactively, in a gradual empirical search, to describe an improving set of adjustment biases for applying scanner measurements to advertised bandwidths. This link illustrates the general principal, though the idea is to design and construct bias curves with polynomials rather then to fit them somehow.