A central problem in building large scale parallel machines is the design of the interconnection network. Interconnection network design is largely constrained by packaging technology. We start with a generic set of packaging restrictions and evaluatte diffrent network organizations under a random traffic model. We identify families of networks (Product of complete graphs, high degree deB ruijn graphs) that we believe will b useful for mutilevel packaging. Our results incicate that customizing is useful. Some of the general principles that arise out of theis study are; 1. Making the networks denser at the lower levels of the packaging hierarchy has a significant positive impact on global communication performance), 2. It is better to organize a fixed amound of communication bandwidth as a smaller number of high bandwidth channels). 3. Providing the processors with the ability to tolerate latencies (by using multithreading) is very useful in improving performance.