This paper presents a switchless, optical interconnect module that serves as a node in a network of identical distribution
modules for large-scale systems. Thousands to millions of hosts or endpoints may be interconnected by a network
of such modules, avoiding the need for multi-level switches. Several common network topologies are reviewed and
their scaling properties assessed. The concept of message-flow routing is discussed in conjunction with the unique
properties enabled by the optical distribution module where it is shown how top-down software control (global routing
tables, spanning-tree algorithms) may be avoided.