Towards Internet in Space: Development of an Address Resolution Protocol and Encapsulation Service for SpaceWire Networks, 10-R9623

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Principal Investigators
Sandra G. Dykes
Robert A. Klar
Allison R. Roberts
Christopher C. Mangels
Buddy J. Walls

Inclusive Dates:  04/01/06 – Current

Background - Spacecraft communications are evolving from shared bus architectures and custom communication protocols toward 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/demultiplexing, and unique hardware addresses.

The two major link-layer switched networks contending for space systems are Ethernet and SpaceWire. Ethernet is the dominant switched network technology on Earth and provides the broadcast, multiplexing, and addressing services necessary to support automatic configuration and management services. The automatic topology discovery and queuing in Ethernet switches increase the mass and power requirements. SpaceWire was designed for the specific requirements of space, including low power consumption, low message latency, and high reliability. However, SpaceWire does not have a broadcast mechanism, nor does it currently support message multiplexing or unique address assignment. Broadcast is necessary for two important automatic network management protocols: Address Resolution Protocol (ARP) and the Dynamic Host Configuration Protocol (DHCP). Consequently, address resolution and host IP assignments on SpaceWire networks require manual configuration.

Approach - We are addressing this deficiency by developing a link-layer broadcast service and a protocol encapsulation service for SpaceWire. Our protocols are designed to work with existing SpaceWire hardware; we require no changes to the SpaceWire specification, routers, or host interface boards. The design is compliant with the SpaceWire specification and can be implemented solely within the interface driver software. Moreover, our approach allows applications to use the standard IP socket API and therefore can conceal all details of the underlying link-layer network. Applications that commonly run over Ethernet will run over SpaceWire networks when hosts use our network driver.

Our project consists of three phases. The first is protocol design and validation by simulation. The second is development of a software driver for the Institute SpaceWire Link Interface Module (SLIM) host interface modules developed under a prior internal research project. The third phase is to construct a SpaceWire testbed to evaluate its performance on an operational network and to serve as a demonstration platform. The demonstration network will include ARP, DHCP, and common networking applications to show how our broadcast protocol enables their use. The technology we are developing under this project provides an important step forward toward improving network management and reducing software development costs on SpaceWire-based systems. This objective is part of the larger vision of rapid deployment and responsive space missions.

Accomplishments - In the first six months of the project, we have developed the protocol specification document, implemented most modules of the SpaceWire IP network driver, and constructed the SpaceWire testbed. Our work has resulted in acceptance of a conference paper at IEEE Aerospace and a conference presentation at the Space Internetworking Workshop. We are participating in the SpaceWire Plug and Play Working Group, which is working on an extension to the SpaceWire standard.

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