  In this paper we investigate the behavior of iteratively decoded low-density
parity-check codes over the binary erasure channel in the so-called ``waterfall
region." We show that the performance curves in this region follow a very basic
scaling law. We conjecture that essentially the same scaling behavior applies
in a much more general setting and we provide some empirical evidence to
support this conjecture. The scaling law, together with the error floor
expressions developed previously, can be used for fast finite-length
optimization.
