Automated File Transfer and Storage Management Concepts for Space

Gary Meyers - GSFC

Ed Criscuolo - CSC

Keith Hogie - CSC

Ron Parise - CSC

Revised 6/14/2004

6/9/2004 2004 Space Internet Workshop 2

Overview

• Introduction

• Concepts

• Testbed Characteristics & Parameters

• Target Mission

• Testbed Architecture & Operation

• Planned simulations

• Results

• Conclusion & Future Efforts

6/9/2004 2004 Space Internet Workshop 3

Introduction

• The purpose of this project was to validate

and demonstrate the use of an IP-based,

NAK-oriented, reliable file delivery protocol

to meet a space mission's data delivery and

storage management requirements for

onboard stored data.

• To this end, we built a Data Delivery

Simulation Testbed and simulated a real,

upcoming mission.

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Concepts

• Instruments generate onboard data as streams of UDP packets.

• Replace onboard "Tape Recorder" paradigm with a file system using random-access files for stored data collection.

• Use IP-based standard "off-the-shelf" file delivery protocols for error-free transfer of stored data.

• Use file-level acknowledgements to automate the management of onboard storage space.

• Trade retransmissions and/or application-level FEC for BER.

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Testbed Characteristics

• Simulated instrument & housekeeping data generation

• Automated onboard data storage management

• Adjustable Space/Ground link characteristics

• Ground system receipt of all collected data

• The simulation testbed must be highly parameterized in order to accommodate changing requirements and investigate "What if" scenarios.

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Testbed Parameters

• Orbital Period

• Contact Time

• Separate Data Rates for Instruments and S/C Houskeeping

• Collection Time Per Data File

• Onboard storage cache size

• Downlink Data Rate

• Uplink Data Rate

• Link Delay

• Link Bit Error Rate

Revised 6/14/2004 2004 Space Internet Workshop 7

• MMS (Magnetospheric MultiScale) chosen

• Orbit Characteristics– 4-spacecraft constellation– Tetrahedral configuration– Highly elliptical orbit– 4 mission phases, with orbital

periods from 1 to 10 days

• Link Characteristics– Downlink rate = 2 Mbits/sec– Uplink Rate = 2 Kbits/sec– Prop. Delay = 25 mS - 215 mS– One contact (per S/C) per orbit, close to perigee

• Data Rates (per S/C)– Aggregate Rate: 25 Kbits/sec continuously– 4 Instruments: 10 , 5, 5, 3 Kbits/sec– S/C Housekeeping: 2 Kbits/sec

Target Mission

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Testbed Architecture

Inst 110 kbps

Inst 25 kbps

Inst 35 kbps

Inst 43 kbps

Spacecraft C&DH

UDPCapture

UDPCapture

UDPCapture

UDPCapture

MDPServer

Router

Channel Simulator

Router

Ground System

MDP Client

Houskeeping2 kbps

UDPCapture

HotDirectoryOutbox

SimulatedSpace Link:Delay and BER@ 2.0 MbpsOrbit

Simulator

Pause / Resume

Data Archive

DataCollection

Inbox

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Testbed Operation

• UDPCapture continuously transforms data streams of UDP packets into discrete data files onboard.

• Data files are moved to MDP's hot directory when completed.

• Orbit simulator enables MDP server during contact passes.

• When enabled, MDP Server automatically sends any new files that have appeared in the hot directory, and manages onboard data storage space.

• Channel simulator hardware introduces propagation delay and bit errors.

• MDP Client reliably receives data files, automatically requesting retransmission of any bad packets. Files are moved to archive when complete.

6/9/2004 2004 Space Internet Workshop 10

Planned Simulations

• Downlink Data Rate : 2 Mbps

• Uplink Data Rate : 2Kbps

• Link Prop. Delay : 25mS (Phase I & II),215mS (Phase IV)

• BER : 0, 1E-8, 1E-7, 1E-6, 1E-5

• Orbital Periods : 24 hrs (Phase I),4 days (Phase II), 10 days (Phase IV)

• Inst/Hk Data Rates : 10, 5, 5, 3, 2 Kbps (25 Kbps total)

• Collection Time Per Data File (each instrument) : 3 hrs

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Calculated Transfer Times

• Based on previous MDP performance measurements*

(using 1 Mbyte files)

Phase I Phase II Phase IV

0 BER 23 min 82 min 221 min

1E-8 23 min 82 min 221 min

1E-7 26 min 91 min 246 min

1E-6 43 min 152 min 409 min

1E-5 60 min 217 min 508 min

* Refer to "Characterization data for MDP, 2001" http://ipinspace.gsfc.nasa.gov/documents/report_2001_09_29_thru_31.wbk

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Projected Phase I Storage Utilization

MDP Onboard File ManagementServer (kbytes)

0

100000

200000

300000

400000

500000

600000

0 20 40 60 80 100 120 140 160

Elapsed time (hrs)

File Space Used (Kbytes)

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Results

• To date, the Phase I simulations have been run.

• Initial real-time run at 0 BER for 4 days– Transfer times matched analytically derived values.– Storage utilization matched analytically derived values to

within 1%

• Similar results for BERs of 1E-8 & 1E-7

• At BER of 1E-6– Transfer times were slightly better than predicted– Storage utilization matched predicted within 1%

• 30 day run at BER of 1E-5– Transfer times were 30% better than predicted

(43 min vs 60 min)– Storage utilization matched predicted within 1%

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Conclusion & Future Efforts

• Conclusion– An IP-based, NAK-oriented, reliable file delivery

protocol can meet MMS mission's Phase I data delivery and storage management requirements for onboard stored data.

• Future Efforts– Vary MDP block size from 1024 to 1500 and

characterize the effect on goodput– Add pro-active application-level FEC to reduce

retransmissions at BER of 1E-5 and characterize the effect on bandwidth utilization