20 november 2008 sb-1 first look at the deep impact dtn experiment (dinet) scott burleigh jet...
TRANSCRIPT
20 November 2008SB-1
First Look at the Deep ImpactDTN Experiment (DINET)
Scott BurleighJet Propulsion Laboratory
California Institute of Technology
Copyright 2008 California Institute of TechnologyGovernment sponsorship acknowledged.
20 November 2008SB-2
DINET Summary• The purpose of the DINET project is to demonstrate NASA’s
implementation of the IRTF-conformant open Delay-Tolerant Networking protocols (Interplanetary Overlay Network – “ION”) in flight and ground software functioning at Technology Readiness Level 7 or 8, making it ready for use by space flight projects.
• Plan:– Upload ION software to the Deep Impact “flyby” spacecraft during inactive
cruise period, while the spacecraft is en route to encounter comet Hartley 2.
– Use the DI (now “EPOXI”) spacecraft as a DTN router for image bundles flowing from one lab machine to another, over interplanetary links.
– Use the Deep Space Network tracking stations: eight tracking passes of 4 hours each, separated by intervals of 2 to 5 days. Uplink at 250 bytes/sec, downlink at either 110 or 20,000 bytes/sec.
– On the last four passes, induce data loss by randomly discarding 1/32 of all received packets, thus forcing the exercise of LTP retransmission.
– One-way signal propagation delay is initially 81 seconds, drops to 49 seconds by the end of the four-week exercise.
– Use AMS publish/subscribe over BP/LTP to send about 300 small images through this network, via the spacecraft. Track statistics, display on reception.
20 November 2008SB-3
The DINET Stack
CCSDS TM/TC
X-band R/F
LTP retransmission
BP forwarding
CCSDS spacepackets
AMSmessaging
Remote AMScompression
Convergence layer adapter
Link service adapter
image publisher/receiver
load/go utilityfor network administration
adminprograms,rfx system,
clocks
20 November 2008SB-4
Load/Go
Deep Impact DSOT DINET EOC in PTL
7
3
2
5
4
16
6
10
stotEVRs
“Earth”
“Mars”
“Phobos”
Experimentdatabase
Load/GoLoad/Go
bundles
log msgsBRS
TCP
space links
image files
image files
LTP/UDP
8
12
20
serverclient
serverclient
serverclient
Experiment 1: Send images from nodes 12 to node 8 via nodes 6, 3, 7 (the Deep Impact spacecraft), 2, 4. Also send images from nodes 20 to node 8 via nodes 10, 5, 7 (the Deep Impact spacecraft), 2, 4.
NOTE: Deep Impactscience spacecraftis functioning as arouter (infrastructure).
20 November 2008SB-5
Load/Go
Deep Impact DSOT DINET EOC in PTL
7
3
2
5
4
16
6
10
stotEVRs
“Earth”
“Mars”
“Phobos”
Experimentdatabase
Load/GoLoad/Go
bundles
log msgsBRS
TCP
space links
image files
image files
LTP/UDP
8
12
20
serverclient
serverclient
serverclient
Experiment 2: Send Load/Go directive loads from node 16 to node 12 via nodes 4, 2, 7, 3, 6. Also from 16 to 20 via 4, 2, 7, 5, 10.
20 November 2008SB-6
Load/Go
Deep Impact DSOT DINET EOC in PTL
7
3
2
5
4
16
6
10
stotEVRs
“Earth”
“Mars”
“Phobos”
Experimentdatabase
Load/GoLoad/Go
bundles
log msgsBRS
TCP
space links
image files
image files
LTP/UDP
8
12
20
serverclient
serverclient
serverclient
Experiment 3: Omit a contact between 7 and 5 and repeat, forcing images from 20 to travel via 10, 6, 3, 7, 2, 4 and forcing directive loads to 20 to travel via 4, 2, 7, 3, 6, 10.
XNOTE: spacecraft is temporarily unable to function as a router.
20 November 2008SB-7
Load/Go
Deep Impact DSOT DINET EOC in PTL
7
3
2
5
4
16
6
10
stotEVRs
“Earth”
“Mars”
“Phobos”
Experimentdatabase
Load/GoLoad/Go
bundles
log msgsBRS
TCP
space links
image files
image files
LTP/UDP
8
12
20
serverclient
serverclient
serverclient
Experiment 4: manually route traffic between nodes 12 and 20 (both remote) via the orbiter, without Earth in the loop from node 20 to 12 and 12 to 20.
20 November 2008SB-8
Configuration Parameters
• Convergence-layer protocols:– “Bundle Relay Service” (TCP) through firewall between DSOT and EOC nodes.– LTP (“red”) on all other links, over CCSDS TM/TC (flight) or UDP/IP (ground).
• Images sent at priorities 0, 1. Network mgt traffic, custody signals, critical images sent at priority 2.
• Custody transfer on all application bundles.
• All bundles are CBHE-compressed.
• Bundle status reports are sent only on destruction of custodial bundles.
• Time-to-live is 10 days for all image bundles.
• Max bundle size is 64 KB. Max LTP segment size is 739 bytes.
• Contact Graph Routing used to compute routes dynamically.– Intermittent cross-link between nodes 6 and 10 enables alternative paths.
20 November 2008SB-9
Results
• Moved 292 images (about 14.5 MB) through the network.– Still working on performance analysis, metrics.
• No data loss other than nominal time-to-live expiration.
• No data corruption anywhere in the network.
• Aside from the uploading of spacecraft clock drift corrections, the network operated continuously without operator intervention throughout the four weeks of the experiment.
20 November 2008SB-10
Key Findings
• The protocols work well.– Signal propagation delays of 49 to 89 seconds were tolerated.– End-to-end latencies on the order of days were tolerated.– Station handovers and transient failures in DSN uplink service were handled
automatically and invisibly.– Protocol overhead was minimal.– Dynamic route computation was generally successful.
• The software is highly stable.– No software failures in four weeks of continuous operation on VxWorks, Solaris,
and Linux platforms.– No effect on the operation of other flight software.– No leakage of memory or non-volatile storage space.
• Clock synchronization and OWLT estimation errors of several seconds had no noticeable effect on network operation.
Problems
• Several bugs in Contact Graph Routing resulted in some under-utilization of network capacity. Revisions in progress.
• Spacecraft clock drifted more rapidly than expected – over 1 second per day. Revised clock correction deltas had to be uploaded to ION for each tracking pass.
• Various other minor bugs, plus one DSN hardware problem revealed when processing high volume of uplink traffic.
20 November 2008SB-11
Conclusion
• Fully automatic operation of a DTN over deep space links is feasible.
20 November 2008SB-12