This paper describes a COTS bus network architecture consisted of the IEEE 1394 and SpaceWire buses. This architecture is based on the multi-level fault tolerance design methodology proposed by Chau but has much less overhead than the original IEEE 1394/I 2 C implementation. The simplifications are brought about by the topological flexibility and high performance of the SpaceWire. The SpaceWire can form a connected graph that embeds multiple spanning trees. This is a significant advantage because it allows the IEEE 1394 bus to select a different tree topology when a fault occurs. It also has sufficient performance to stand in for IEEE 1394 bus during fault recovery, so that a backup IEEE 1394 bus is no longer required. These two buses are very compatible at the physical level and therefore can easily be combined. Analysis of the effectiveness of the IEEE 1394/SpaceWire architecture shows that it can achieve the same fault tolerance capability as the IEEE 1394/I 2 C architecture with less redundancy.