Ethernet Over SpaceWire - Hardware Issues
- Paper number
IAC-06-B5.7.01
- Author
Dr. Barry Cook, 4Links Limited, United Kingdom
- Coauthor
Mr. Paul Walker, 4Links Limited, United Kingdom
- Year
2006
- Abstract
This paper considers 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 will consider how existing Ethernet-based designs can be implemented on SpaceWire networks. A companion paper will consider the software to support such networks. These papers reflect the result of building an experimental network with SpaceWire physical layer and software support incorporated in a Linux device driver. This paper will compare SpaceWire and Ethernet, noting the similarities and differences, and will address the issues concerning how to make Ethernet work over SpaceWire. 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 Rad-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 connexions 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; behaviour 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). The authors have experience of building routing switches and test equipment for SpaceWire and Ethernet, and of building fault-tolerant dynamic plug-and-play systems for SpaceWire. From this experience, their conclusion is that it IS possible to run Ethernet over SpaceWire, and that it is possible to do so at reasonable cost.
- Abstract document
- Manuscript document
IAC-06-B5.7.01.pdf (🔒 authorized access only).
To get the manuscript, please contact IAF Secretariat.