Asynchronous Message Service (1 of 3)

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