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Multi-Link Iridium Satellite Data Communication System

Multi-Link Iridium Satellite Data Communication System. Overview, Performance and Reliability from Summer 2004 SUMMIT , Greenland Field Experiments July 14-July 25, 2004 Abdul Jabbar Mohammad, Said Zaghloul, Graduate Research Assistants Dr.Victor Frost, Dan F. Servey Distinguished Professor

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Multi-Link Iridium Satellite Data Communication System

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  1. Multi-Link Iridium Satellite Data Communication System Overview, Performance and Reliability from Summer 2004 SUMMIT, Greenland Field Experiments July 14-July 25, 2004 Abdul Jabbar Mohammad, Said Zaghloul, Graduate Research Assistants Dr.Victor Frost, Dan F. Servey Distinguished Professor (August 22, 2003)

  2. Presentation Outline • Previous Work • 4-Channel System • Conclusions from 2003 Field Experiments • 8-Channel Iridium System • Design • Integrated Unit • GUI Software • Analysis • Network Architecture • 2004 Field Experiments • Field Implementation • Results • Conclusions and Future Work

  3. Remote System PPP client Iridium Gateway USB-SERIAL I. Modem 1 Antenna Grid I. Modem 2 I. Modem 3 I. Modem 4 Remote Subsystem Local System PPP Server Multi-port PCI card PSTN Modem Pool Local Subsystem 4-Channel Iridium System (Tested in Summer 2003) • 4 Iridium – 4 PSTN data configuration • Discrete components • Patch antennas • Control software on a rugged Laptop

  4. Conclusions from 2003 field experiments • Developed a reliable multi-channel data communication system based on Iridium satellites that provide round the clock, pole-to-pole coverage. • Developed console based link management software that ensures fully autonomous and reliable operation • An end-to-end network architecture providing Internet access to science expeditions in Polar Regions was demonstrated. • The system efficiency was observed to be >90%. With 4-modems the average end-to-end throughput was found to be 9.26 Kbps • The round trip time of the system in Iridium-PSTN configuration was significant ~1.8 sec • The average up-time of the overall connection was approx 90%. The average time interval between primary call drops was 100 minutes • Mobile tests showed performance very similar to that of stationary system up to speeds of 20mph • 4-Iridium to 4-PSTN configuration was found to be stable of autonomous operation

  5. Conclusions from 2003 field experiments • The USB-to-serial converter used for multiple serial ports was not stable resulting in system failures. • Interaction of PPP level compression with control software results in corrupted modem termination, resulting in significant packet loss • Identified areas for additional research • Evaluate the new data-after-voice (DAV) service from Iridium • Improve the user friendliness of the system • Research into the spacing and sharing of antennas to reduce the antenna footprint • Increase the the system capacity by scaling the system from 4 to 8 channels • Develop a fully integrated plug and play system that can be deployed easily in the field

  6. 8-channel Iridium System – Design Elements • Integrated 8 Iridium modems and all the components in an 19” rack mount unit. • On-board computer to run the control software • Single board EBX format system ( P-III, 1 GHz, 512 MB RAM) • Extended temperature operation (-300 C to + 800 C ) • PC104 type multi-port serial card with 8 DB9 ports (extended temp operation) • Integrated 5”x4” LCD screen, front panel flips down to hold the keyboard/mouse • Single linear power supply for the 8 modems and on-board computer • Developed a new GUI based management/control software, that configures the unit in all the data modes: a) Iridium-Iridium DAV mode, b) Iridium-Iridium data mode, c) Iridium-PSTN mode • Replaced the patch antennas with inverted cone antennas that can be easily mounted on field and do not need a external ground plane.

  7. 8-channel Iridium System – Integrated Unit Bottom View Top View 19” 24” Front View • Dimension : 9x19x24 inch • Weight : 50 lbs • Operating temp : -30 to 60 c • Power input : 120 V AC • Replication Costs : ~$18,000 9”

  8. 8-channel Iridium System – Client Software Client Software consists of three modules: Graphical User Interface • Easy Configuration and Operation • Does not require experienced users Control Software • It is the core of the software • Automatic Modem Control XML Database • Registers all call drops and retrials • Makes it possible for future analysis of network performance data

  9. 8-channel Iridium System – Client GUI

  10. 8-channel Iridium System – Client GUI

  11. HTTP TCP UDP FTP 8-channel Iridium System – Analysis Machine A Machine B System Model • Application: FTP, HTTP • Agent: TCP, UDP • MLPPP • 8 Modem Links App App Agent Agent Iridium Network Modems Model • Each link has a dropping probability • Each link has a probability of error 8 Modem Links MLPPP MLPPP

  12. SUMMIT Camp, Greenland 100 Mbps Ethernet (Default gateway) (Default gateway) user 4 PPP Server PPP Client ITTC Default Router P-T-P Satellite link eth0 ppp0 ppp0 eth0 100 Mbps Ethernet User 2 User 1 user 3 user 1 User 3 Camp WI-FI user 2 World Wide Web ITTC Network, University of Kansas 8-channel Iridium System –Network Architecture

  13. Field Experiments – System Implementation 8-Channel system in a weather-port at SUMMIT camp in Greenland, July 2004

  14. Field Experiments – Antenna Setup 4 ft 10 ft 8 Antenna setup at SUMMIT camp in Greenland, July 2004

  15. Results – Throughput • Average throughput efficiency was observed to be 95% • The above results are from the test cases where no call drops were experienced • In event of call drops the effective throughput of the system will be less than the above values

  16. Results – Throughput FTP throughput observed during data transfer between the field camp and KU • Average throughput during the FTP upload of large files was observed to be 15.38 Kbps • Due to call drops, the efficiency was reduced to ~80% • Detailed TCP analysis based on IPERF and FTP data is in progress

  17. Results – Round Trip Time • Average RTT = 1.4 sec • Minimum observed RTT = 608 msec • Mean deviation = 800 msec • Detailed analysis in progress

  18. Uptime % 89 95 96 97 97 97 97 98 Results – Reliability: 14th July 12-hr test • Call drop pattern during 8 Iridium – 8 Iridium DAV mode test for 12 hrs • Percentage uptime with full capacity (8 channels) is 89% and with at least one modem is 98% • Total number of primary call drops during 12 hrs = 4 • Average time interval between call drops is ~ 180 mins

  19. 85 92 93 93 94 94 94 96 Results – Reliability: 22nd July 32-hr test Uptime % • Call drop pattern during 8 Iridium – 8 Iridium DAV mode test for 32 hrs • Percentage uptime with full capacity (8 channels) is 85% and with at least one modem is 96% • Total number of primary call drops during 32 hrs = 24 • Average time interval between call drops is ~ 72 mins

  20. Uptime % 67 81 85 85 85 85 85 90 Results – Reliability: 19th July 6-hr test • Call drop pattern during 8 Iridium – 8 PSTN data mode test for 32 hrs • Percentage uptime with full capacity (8 channels) is 67% and with at least one modem is 90% • Total number of primary call drops during 6 hrs = 9 • Average time interval between call drops is ~ 35 mins

  21. Results – Mobile tests Iridium antennas Iridium system mounted in an autonomous vehicle (MARVIN) Experiments monitored from another vehicle through 802.11b link

  22. Uptime % 65 79 82 84 84 85 87 92 Results – Mobile tests • Call drop pattern during 8 Iridium – 8 Iridium DAV mode test for 2 hrs • Percentage uptime with full capacity (8 channels) is 65% and with at least one modem is 92% • Average time interval between call drops is ~ 45 mins • Average throughput = 18.6 Kbps, Average RTT = 2 sec

  23. Applications • Summer 2004 field experiments • Communications data upload – up to 40 MB files • Radar data uploads – up to 55 MB files • Text chat with PRISM group at KU • Video conference - real time audio/video • Individual audio or video conference works with moderate quality with the commonly available codecs • Outreach Use • Daily Journal logs uploaded • Daily Pictures uploaded • Video clips uploaded • Held video conference with science teachers/ virtual camp tour • Wireless Internet access

  24. Conclusions • Integrated 8-channel system • Works out of the box • Reliable and fully autonomous operation • The newly developed GUI based control software • Reduced the field setup time, increased the ease of operation • Suitable for operation by non-technical users • System performance based on field experiments • Average throughput with 8 channels is 18.6 Kbps, efficiency > 90% • Average round trip time using DAV modes is 1.4 sec, significantly less than 1.8 sec of Iridium-PSTN configuration • Average uptime with full capacity using DAV mode was 85 %; better than both non-DAV mode and PSTN mode • Percentage system uptime (at least one mode) was ~95% for all the modes • Average time interval between call drops is 60 mins and varies a lot. • In conclusion, the throughput and delay performance of the system using Iridium-Iridium DAV mode is better than other data modes.

  25. Lessons Learned • The average time interval between call drops reduced from 100 minutes in case of 4 Iridium-4 PSTN system to 60 minutes in case of 8 Iridium – 8 Iridium DAV system. • The call drop pattern as seen in “number of online modems vs. time” characteristics varies over time. (detailed study in progress) • Modem firmware failures were experience for the first time. Modem locks up randomly and needs power cycling. This problem is not very severe and occurred less than 5 times during the field experiments . Further, this issues has been noticed by the other researchers using Iridium for field work. • Mounting of antennas on the mobile vehicle could be improved to increase stability for long duration experiments. While the current mounting works for short duration tests, it is not stable for permanent field operation • Due to a bug in linux pppd software, a call drop on the primary modem still causes the entire bundle to drop.

  26. Future Work to Understand and Enhance the MLPPP Iridium System • The performance of network using the Iridium/MLPPP needs to be evaluated • A system model is needed in order to explain the network behavior and to develop enhancements to the system • Call drops needs to be categorized and reasons for call drops need to be studied • Due to poor signal strength (Low SNR) • Due to Handovers (inter-satellite and intra-cell) • Other reasons • The performance of the TCP RTT measurement algorithm needs to be evaluated over the MLPPP Iridium link

  27. Future Work to Understand and Enhance the MLPPP Iridium System • Analyze call drop pattern. Experiments at ITTC to validate the number of call drops. • Upgrade modem firmware (as it becomes available) to solve the problem of failures. Else the control software should be modified so that it can recognize modem failures and cycle power to that modem. • Develop user-friendly GUI based server software (similar to the client software) to increase the functionality and ease of operation • Research the pppd bug that causes the entire bundle to drop on the event of a primary modem call drop. Modification of PPP networking code could be one solution. • While detailed TCP analysis is in progress, it is evident that a call drop results in a degradation in the system performance. This effect could increase as the propagation distance/delay (e.g. data transfer between Kansas and Antarctica), understanding and then being able to predict such degradations is needed.

  28. Future Work-Research • Delay Tolerant Networking (DTN): Research of new network protocols and methods for reliable data communication among extreme and performance-challenged environments. The efficiency of the standard internet protocols decreases considerably with propagation distance and intermittent connectivity, making them unsuitable for very long distance/intermittent communication. • Communications from Polar Regions involves similar problems as addressed by DTN, e.g., connectivity over low speed links and intermittent connectivity over high speed links. • Methods developed for networks with intermittent connectivity would be suitable for communication over satellite links with frequent call drops as experienced with Iridium.

  29. Future Work-Research • Typical DTN applications involve low bandwidth intermittent (satellite) link and high bandwidth conventional (Internet) links as parts of the same network. Hence, interoperability is a major issue. • A new suite of communication protocols is being researched by the Consultative Committee for Space Data Systems (CCSDS) and Delay Tolerant Networking Research Group (DTNRG). The CCSDS File Delivery Protocol concentrates on a tiered architecture; building over the existing regional protocols wherever possible. Adapting the protocols being developed by CCSDS and DTNRG for polar research in needed.

  30. Future Work-Research Issues • Can the evolving DTN technologies be adapted to enhance communications in polar regions, if so how? • How can optimum DTN system parameters be determined? • What is reliability vs. efficiency of the developed protocols? • Can the Iridium be used to evaluate the new DTN protocols? • Are existing protocols (like CFDP) over satellite networks (Iridium) suitable for polar communications?

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