Ethernet over SpaceWire—Hardware issues

We consider the opportunities for combining the best of SpaceWire, such as modularity, high speed, low latency, fault tolerance, and ease of implementation, with the vast experience of protocol design that has been implemented on Ethernet. We consider how existing Ethernet-based designs can be implemented on SpaceWire networks.Both technologies can be used to create networks that route packets from source to destination. SpaceWire, however, has a physical layer that has proven easier to build into a radiation-hard environment. Ethernet is based on the legacy of a bus and so relies on broadcast with packets visible to all nodes, whereas SpaceWire is entirely point-to-point and allows multiple connections for redundancy, which raises issues for broadcast.Issues that will be addressed to allow Ethernet to work over SpaceWire include converting the Ethernet addressing into SpaceWire routing; behavior in the event of faults (which may create a need to re-route); handling broadcast; and considering whether the network topology is static (as in conventional large spacecraft) or dynamic with plug and play (as suggested for responsive space on small satellites, or for the Shuttle/CEV). Further benefits will be described, for example the use of Ethernet protocols designed specifically for unreliable networks may significantly reduce cost by reducing or removing the need for upset mitigation techniques such as triple-modular redundancy (TMR).