Towards Internet in Space: Development of an Address Resolution Protocol and Encapsulation Service for SpaceWire Networks, 10-R9623Printer Friendly Version
Inclusive Dates: 04/01/06 09/30/07
Background - Spacecraft communications are evolving from shared bus architectures and custom communication protocols to on-board switched networks and standard protocols. The use of standard networking software such as the Internet Protocol (IP) suite with its wealth of software development and network management tools can substantially reduce development time, errors, and cost. To take advantage of these tools, the underlying link-layer network must provide certain functions including broadcast, message multiplexing and de-multiplexing, and unique hardware addresses.
Two candidates for on-board networks are Ethernet and SpaceWire. Ethernet is the dominant local network technology on Earth but is problematic for spacecraft because its store-and-forward queuing of data packets induces unpredictable transmission delay. SpaceWire was designed for spacecraft requirements of low power consumption, low message latency, and high reliability. The drawback to SpaceWire is that it does not have a broadcast mechanism and does not provide for unique device addresses. These features are necessary for standard network configuration and management tools such as the Address Resolution Protocol (ARP) and the Dynamic Host Configuration Protocol (DHCP). Without broadcast support, each host on a SpaceWire network must be manually configured and manually updated whenever a device is added, removed, or moved to a different network location.
Approach - This deficiency was addressed by developing a distributed broadcast service and a protocol encapsulation service for SpaceWire. This approach allows standard IP network configuration and management applications to be used on SpaceWire networks, eliminating the need for manual configuration. The protocols are implemented solely within the interface driver software and therefore require no changes to application software, SpaceWire routers, or SpaceWire interface hardware.
For an earlier internal research effort, SwRI developed the SpaceWire Link Interface Module (SLIM) board, which was used to test new protocols. The first step in this project was to develop a Linux network device driver for the SLIM board. The device driver integrates with the Linux TCP/IP stack on one side and with the SLIM hardware on the other side. SwRI protocols were incorporated into the driver in a manner that is transparent to application software, allowing the same network applications such as a web server, DHCP, or ping to run over both Ethernet and SpaceWire networks.
SwRI evaluated performance of the broadcast protocol with simulation studies, analytical analysis, and tests of our implementation on a SpaceWire network testbed. Testbed results confirm that the broadcast protocol operates correctly with ARP, ping, and other communication software. Analytical and simulation results show that the distributed nature of the protocol has lower overhead and message delay than a centralized approach, and can be effective at reducing “hot spots” of network congestion.
Accomplishments - This project led to five referred conference papers, four conference presentations, and a presentation at the European Space Agency SpaceWire Working Group meeting. It has been a catalyst for making numerous contacts within many research communities, including groups at NASA, ESA, and AFRL. The principal investigator served on the program committee for the 1st International SpaceWire Conference, team members were active in the SpaceWire Plug-and-Play Working Group, and were invited guests at review meetings for the AFRL PnPSat program.