17 November 20041

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.

17 November 20042

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.

17 November 20043

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.

17 November 20044

Deep Space Communications Architecture

(no retransmission, no store-and-forward)

User application

UT adapter

CFDP file system functions

“UT layer”

CFDP unacknowledged transmission

LTPpoint-to-point

retransmission

Bundling store-and-forward

TM/TC, AOS Prox-1

R/F, optical

TCP end-to-endretransmission

Ethernet

wire

COP/Pretransmission

IP network routing

7

4

3

2

1

(bandwidth management)

AMS

UT adapter