1. 17 November 2004 1 Asynchronous Message Service (1 of 3) In addition to file transfer, event-driven asynchronous message exchange may also be useful for deep space communications with and among spacecraft : –streaming engineering (housekeeping) data –real-time commanding –continuous collaborative operation among robotic craft NASA’s proposed new Command, Control, Communications, and Information (C3I) architecture is based on this model. Challenges in large-scale asynchronous message exchange: –Heterogeneity: platforms, security regimes, communication environments, QOS requirements, performance requirements, cost tolerance. –Changing topology: requires autonomous discovery of communication endpoints, automatic reconfiguration. –Publish/subscribe message exchange model scales better than client/server.

2. 17 November 2004 2 Asynchronous Message Service (2 of 3) But most asynchronous message exchange systems are: –proprietary, licensed products (e.g., TIBCO Rendezvous, NDDS) rather than open international standards; –not designed for operation on deep space robots. Proposed CCSDS Asynchronous Message Service (AMS) standard is based on proven NASA technology: no commercial licensing, designed for spacecraft flight operations. Tramel (Task Remote Asynchronous Message Exchange Layer) was developed in JPL’s Flight Systems Testbed (FST) in 1995- 1996; mature and stable since 1998. –Real-time spacecraft simulation in FST (1994-1999). –Software fault tolerance experiments at JPL (1998). –X-34 Integrated Vehicle Health Management testbed (2003). –Baselined for inclusion in C3I.

3. 17 November 2004 3 Asynchronous Message Service (3 of 3) AMS features: –Platform-neutral, UT-layer neutral. –Designed to scale from very small to very large configurations. –Self-configuring and fault-tolerant, via silent “meta-AMS” protocol. –“Remote AMS” adaptations enable efficient, delay-tolerant publish/subscribe capability over interplanetary distances. Status: –Concept paper (tentative protocol specification) ready for review. –Fully-functional, well-documented prototype (Tramel) has been mature for six years.

4. 17 November 2004 4 Deep Space Communications Architecture (no retransmission, no store-and-forward) User application UT adapter CFDP file system functions “UT layer” CFDP unacknowledged transmission LTP point-to-point retransmission Bundling store-and-forward TM/TC, AOSProx-1 R/F, optical TCP end-to-end retransmission Ethernet wire COP/P retransmission IP network routing 7 4 3 2 1 (bandwidth management) AMS UT adapter