MDP: Reliable File Transfer for Space Missions : MDP: Reliable File Transfer for Space Missions James Rash
NASA/GSFC
Greenbelt, MD 20771
Ed Criscuolo, Keith Hogie, Ron Parise
Computer Sciences Corp
June 11, 2002 2002 Earth Science Technology Conference http://ipinspace.gsfc.nasa.gov/
Reference Architecture for Flight MDP : 2002 Earth Science Technology Conference 2 Reference Architecture for Flight MDP Based on Internet suite of protocols
IP is the common thread
All upper layers sit on top of IP
Multicast Dissemination Protocol application layer, UDP transport
Bulk Data Transfers in Space : 2002 Earth Science Technology Conference 3 Old Paradigm: Recorder Playback
Legacy Architecture
Emulation of Sequential Tape Recorder
FEC Only
Preformatted Downlink Frames on Tape
Manual Retransmission of Whole Data Set
Complicated Onboard Storage Management
New Paradigm: File Transfer
Modern OS That Supports Files
Random Access Playback
FEC and/or Retransmission Protocol
Isolation of Application Science Data from Link Formatting
Automatic Retransmission at Packet Level
Automatic Storage Management Bulk Data Transfers in Space
General Description of MDP : 2002 Earth Science Technology Conference 4 General Description of MDP UDP-based reliable file transfer protocol
Designed for multicast environments, but addresses many of the same issues as space missions:
Bandwidth Utilization - as high as 90%
Delay Tolerance - uses connectionless UDP transport
Noise Tolerance - automatic retransmission of dropped packets
High Link Asymmetry - 10,000:1 and higher typical
Unidirectional Link Capability - connectionless UDP transport
Intermittent Link Tolerance - Loosely coupled session
Implemented in two pieces:
Protocol Library
File Transfer Application
Open Source available @ http://pf.itd.navy.mil/
Data-Flow Architecture: Direct to User : 2002 Earth Science Technology Conference 5 Data-Flow Architecture: Direct to User
Data-Flow Architecture: Store and Forward : 2002 Earth Science Technology Conference 6 Data-Flow Architecture: Store and Forward
MDP Parametric Study: Test Setup : 2002 Earth Science Technology Conference 7 MDP Parametric Study: Test Setup Automated Test
Insert Spacelike Delay and Noise
Collect Server, Router, and Client Statistics
Independent Control Path
MDP Parametric Study: Results : 2002 Earth Science Technology Conference 8 MDP Parametric Study: Results MDP Bandwidth Utilization vs RTT
MDP Parametric Study: Results : 2002 Earth Science Technology Conference 9 MDP Parametric Study: Results MDP Link Asymmetry vs RTT
Upcoming MDP Flight Tests : 2002 Earth Science Technology Conference 10 Upcoming MDP Flight Tests Communication and Navigation Demonstration on Shuttle (CANDOS)
16 Day HitchHiker Mission
ST-107, Summer of 2002
CANDOS will demonstrate:
Basic IP connectivity on the space link
Mobile-IP routing through multiple ground stations
Reliable file transfer using MDP, including:
Intermittent contacts during transfers
Downlink-only unidirectional contacts
Future Enhancements to MDP Application : 2002 Earth Science Technology Conference 11 Future Enhancements to MDP Application Runtime Control Interface
Runtime Data Rate Throttle Control
Checkpoint / Restore
Pause / Resume
React to Receiver State
Per-object Status for Positive File ACK
Future Enhancements to MDP Application : 2002 Earth Science Technology Conference 12 Future Enhancements to MDP Application Runtime Control Interface
Current application controlled from command line parameters at startup
A runtime TCP port will be added to allow changing settings without stopping and restarting the application
Runtime Data Rate Throttle Control
Since MDP uses UDP it must throttle its output
The output rate may need to change as a spacecraft uses SN and GN links at different rates
Checkpoint / Restore
Saving state information is important if the client or server needs to be restarted or if the operating system restarts
This is needed for long-term operation scenarios
Future Enhancements to MDP Application : 2002 Earth Science Technology Conference 13 Future Enhancements to MDP Application Pause / Resume
If the MDP server knows its transmit link is no longer available, it should “pause” and stop trying to send data
Sending data when the transmit link is off wastes onboard processing power and causes more retransmission NACKs
React to Receiver State
If the spacecraft does not have receiver lock, this will suppress sending the final positive file ACK since it will not hear the response
Per-object Status for Positive File ACK
Currently MDP waits for the ACK from one file before starting the next
In some scenarios MDP needs to continue on without waiting
Standardization Activities : 2002 Earth Science Technology Conference 14 Standardization Activities http://ipinspace.gsfc.nasa.gov/ Reliable Multicast Transport Working Group (RMT)
http://www.ietf.org/html.charters/rmt-charter.html
Standardize reliable multicast protocols
One-to-Many bulk data transport
Building-Block Approach to Protocol Specification
Allows blocks to be used in within multiple protocols
Three Protocol Instantiations:
NORM: Nack Oriented Reliable Multicast
(successor to MDP)
TRACK: TRee ACKnowledgement based protocol
ALC: Asynchronous Layered Coding
(FEC based with no feedback)