Overview, Performance and Reliability from Summer 2003 NGRIP, Greenland

1
Iridium Based Data Communication System

• Overview, Performance and Reliability from Summer
  2003 NGRIP, Greenland
• Field Experiments
• June 23-July 17, 2003
• Abdul Jabbar Mohammad, Graduate Research
  Assistant
• jabbar_at_ittc.ku.edu
• Dr.Victor Frost, Dan F. Servey Distinguished
  Professor
• Electrical Engineering and Computer Science
• frost_at_eecs.ku.edu

2
Multi-Link Iridium Satellite Data Communication
System for Polar Expeditions

• Motivation
• Polar Radar for Ice Sheet Measurements (PRISM)
• The communication requirements of PRISM field
  experiments in Greenland and Antarctica include
• Data telemetry from the field to the University
• Access to University and web resources from field
• Public outreach to increase the interest of
  student community (K-12) in scientific research
  and enable the science community to virtually
  participate in polar expeditions
• Generic data communication for Remote field
  research
• Mainstream communication system for polar science
  expeditions, field camps in Arctic/Antarctic and
  other research purposes
• Government and security use
• Solution
• Implement a multi-link point-to-point Iridium
  communication system to combine multiple
  satellite links to obtain a single logical
  channel of sufficient aggregate bandwidth.

3
Background - Inverse Multiplexing
Traditional Multiplexing - Data from a multiple
applications/users sent over a single high
bandwidth link. Inverse Multiplexing - Data from
a single application is fragmented and or
distributed over multiple low bandwidth
links. Increases the available bandwidth per
application significantly Multi-link
point-to-point protocol (MLPPP), an extension to
the PPP is a packet based inverse multiplexing
solution Overhead of 12 bytes Fragmentation of
network layer protocol data units (PDUs) into
smaller segments depending upon the PDU size,
link MTUs and the number of available links.
Inverse multiplexing
4
System Architecture
5
4-Channel System
6
4-Channel System Software Overview

• Linux based system
• Open source PPP package
• Custom software developed at University of Kansas
• Chat scripts for Iridium modems
• PPP script to tune link parameters for Iridium
  satellite system
• Client-Server configuration
• Autonomous operation-connection setup, user
  authentication, detecting failures,
  reconnections, handling power failures/system
  resets, generating status information (text)

7
Field Tests and Results Field implementation
Test Location
8
Results Delay Measurement

• Random variation of delay
• High mean deviation
• Delay increases linearly with packet size
• Normalized delay is almost constant for MTU sizes
  gt 800 bytes

• 56 100 200 300 500
  800 1000
  1200 1500

9
Results Throughput

• Tools used TTCP, IPERF
• Throughput varies to some extend due to RTT
  variation
• Efficiency gt 90

Effective throughputs during large file transfers
(K b p s)
10
Results Reliability 10th July 24 hr test
Call drops on the first modem
Total 13 Call drops
Uptime
80.6 91.8 94.7 96.8
11
Results Mobile Performance
Throughput vs. Time
Avg. Throughput 9.34 Kbps
12
Applications Uploads and Downloads

• Files were downloaded to support the science and
  operations of the camp. The importance of each
  file to the user is noted on a subjective scale
  of 1-10,10 being the most valuable.

13
Applications WI-FI setup integrated with Iridium

• The system was useful for general camp purpose
  sending drawings to order spares for a broken
  caterpillar, excel spreadsheet for food order,
  general press releases, downloading weather
  reports for planning C-130 landings

14
Eight Modem Iridium System for 2004 Field
Experiments

• The Modem/Computer box is a 19 rack mount 5U
  equivalent
• The front panel is 8.72 tall and 19 wide. The
  sides are 8.34 tall and 24 deep.
• Weight approximately 45lbs.
• Reproduction cost 18,000

Iridium Modems
Ethernet
USB
15
Lessons Learned

• Multi-link PPP is relatively efficient over
  Iridium system. With 4-modems efficiency was
  observed to be gt90, i.e., over 9Kb/s.
• The average up-time of the overall connection is
  good gt 95
• The RTT the system is significant 1.8 seconds,
  which is an impairment to real time interactions
• There is a large (random) variation in packet
  delay
• Mobile performance very similar to that of the
  stationary system up to speeds of 20mph
• An end-to-end network architecture providing
  Internet access to science expeditions in Polar
  Regions was demonstrated.
• The overall system is reliable, easily scalable,
  lightweight, and available to provide round the
  clock, pole-to-pole coverage.
• The developed link management software ensures
  fully autonomous and reliable operation
• This system provided for the first time, Internet
  access to NGRIP camp in Greenland and
  quantitatively evaluated the system performance
  in terms of delay, packet loss and the call drop
  pattern.