Rent?s rule is a powerful tool for exploring VLSI design and technology scaling issues. This paper applies the principles of Rent?s rule to the analysis of Networks-on-chip (NoC). In particular, a bandwidth-version of Rent?s Rule is derived, and its implications for future NoC scaling examined. Hop-length distributions for Rent?s and other traffic models are then applied to analyse NoC router activity. For fault-tolerant design, a new type of router is proposed based on this analysis, and it is evaluated for routability and its impact on congestion by further use of the hop-length distributions. It is shown that the choice of traffic model has a significant impact on scaling behaviour, design and fault-tolerant analysis.