Recent advances in computer processing speeds have resulted in a parallel processing environment in which the interconnection networks (INs) themselves are the limiting factor in terms of performance. Larger and faster INs can be implemented optically subject to the current limitation in the number of wavelengths imposed by optical switch and filter technology if the INs are arranged hierarchically, i.e. if the processing nodes are arranged in clusters and these clusters are connected together special routing nodes at one or more higher levels. HORN uses optically connected rings as the basic building blocks and connects these rings using an optical tree. Three key issues facing HORN are addressed in this paper: dynamic channel allocation (DCA), optical power budget (OPE) and bit error rate (BER). Four approaches to DCA are evaluated and a design trade-off is performed between them. The first two are taken from the literature while the last two are proposed here and exploit the multiple paths available in a hierarchical network. The evaluation of OPE and BER shows that HORN is feasible and practical when optical amplification is used at the initial signal insertion point for transmissions at higher levels in the hierarchy.