Earth Science Technology Conference

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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)