Future real-time applications requiring massively parallel computer systems also put high demands on the interconnection network. By connecting several WDM star clusters by a backbone star, forming a star-of-stars network, we get a modular high-bandwidth network. In this paper we show how to achieve time-deterministic packet switched communication in such networks, even for inter-cluster communication. An analysis of how the deterministic latency and node bandwidth vary with design parameters is presented. We also propose a general clock-synchronization scheme, improving the worst-case latency with up to 33 percentages.