# Presentation: 279771

## 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

**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**

- 2002 Earth Science Technology Conference

## Bulk Data Transfers in Space

** ****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**

- 2002 Earth Science Technology Conference

## 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/**

- 2002 Earth Science Technology Conference

## Data-Flow Architecture: Direct to User

- 2002 Earth Science Technology Conference

## Data-Flow Architecture: Store and Forward

- 2002 Earth Science Technology Conference

## MDP Parametric Study: Test Setup

** ****Automated Test**
** ****Insert Spacelike Delay and Noise**
** ****Collect Server, Router, and Client Statistics**
** ****Independent Control Path**

- 2002 Earth Science Technology Conference

## MDP Parametric Study: Results

**MDP Bandwidth Utilization vs RTT**

- 2002 Earth Science Technology Conference

## MDP Parametric Study: Results

**MDP Link Asymmetry vs RTT**

- 2002 Earth Science Technology Conference

## 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**

- 2002 Earth Science Technology Conference

## 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**

- 2002 Earth Science Technology Conference

## 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**

- 2002 Earth Science Technology Conference

## 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**

- 2002 Earth Science Technology Conference

## 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)**

- 2002 Earth Science Technology Conference