Multi-Link Iridium Satellite Data Communication System

30
University of Kansas 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)

description

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 - PowerPoint PPT Presentation

Transcript of Multi-Link Iridium Satellite Data Communication System

Page 1: Multi-Link Iridium Satellite Data Communication System

University of Kansas

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)

Page 2: Multi-Link Iridium Satellite Data Communication System

University of Kansas2

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

Page 3: Multi-Link Iridium Satellite Data Communication System

University of Kansas3

4-Channel Iridium System (Tested in Summer

2003)

Iridium Gateway

PSTN

US

B-

SE

RIA

L I. Modem 3

I. Modem 4

I. Modem 2

I. Modem 1 An

ten

na

G

ridM

ulti-

po

rt PC

I ca

rd

Remote System

PPP client

Local System

PPP Server

Modem Pool

Remote Subsystem

Local Subsystem

4 Iridium – 4 PSTN data configuration

Discrete components

Patch antennas

Control software on a rugged Laptop

Page 4: Multi-Link Iridium Satellite Data Communication System

University of Kansas4

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

Page 5: Multi-Link Iridium Satellite Data Communication System

University of Kansas5

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

Conclusions from 2003 field experiments

Page 6: Multi-Link Iridium Satellite Data Communication System

University of Kansas6

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.

Page 7: Multi-Link Iridium Satellite Data Communication System

University of Kansas7

8-channel Iridium System – Integrated Unit

9”

19”

24”

Bottom View Top View

Front View

Dimension : 9x19x24 inch

Weight : 50 lbs

Operating temp : -30 to 60

c

Power input : 120 V

AC

Replication Costs :

~$18,000

Page 8: Multi-Link Iridium Satellite Data Communication System

University of Kansas8

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

Page 9: Multi-Link Iridium Satellite Data Communication System

University of Kansas9

8-channel Iridium System – Client GUI

Page 10: Multi-Link Iridium Satellite Data Communication System

University of Kansas10

8-channel Iridium System – Client GUI

Page 11: Multi-Link Iridium Satellite Data Communication System

University of Kansas11

8-channel Iridium System – Analysis

App

Agent

8 Modem Links

MLPPP MLPPP

Iridium Network

System Model

Application: FTP, HTTP

Agent: TCP, UDP

MLPPP

8 Modem Links

Modems Model

Each link has a dropping probability

Each link has a probability of error

App

Agent

Machine A Machine B

HTTP

FTP

TCP

UDP

Page 12: Multi-Link Iridium Satellite Data Communication System

University of Kansas12

8-channel Iridium System –Network Architecture

SUMMIT Camp, Greenland

ITTC Network, University of Kansas

World Wide Web

User 2

User 3

User 1

ppp0 eth0

PPP Server

ppp0 eth0

PPP Client

P-T-P Satellite link

ITTC Default Router

(Default gateway)(Default gateway) user 4

user 3

user 2user 1

Camp WI-FI

100 Mbps Ethernet

100 Mbps Ethernet

Page 13: Multi-Link Iridium Satellite Data Communication System

University of Kansas13

Field Experiments – System Implementation

8-Channel system in a weather-port at

SUMMIT camp in Greenland, July 2004

Page 14: Multi-Link Iridium Satellite Data Communication System

University of Kansas14

Field Experiments – Antenna Setup

4 ft

10 ft

8 Antenna setup at SUMMIT camp in Greenland, July 2004

Page 15: Multi-Link Iridium Satellite Data Communication System

University of Kansas15

Results – Throughput

Variation of throughput with number of modems

2.49

4.97

6.93

8.98

12.08

13.90

16.43

18.60

02468

101214161820

1 2 3 4 5 6 7 8Number of modems

Thr

ough

put (

Kbp

s)

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

Page 16: Multi-Link Iridium Satellite Data Communication System

University of Kansas16

Results – Throughput

Size of file in MB Approx. Upload Time Effective Throughput in Kbps

1.38 0:11:24 16.53

3.77 0:35:42 14.42

5.62 0:46:12 16.61

15.52 2:30:00 14.12

20.6 3:00:00 15.62

35.7 5:15:00 15.47

55.23 9:00:00 13.96

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

Page 17: Multi-Link Iridium Satellite Data Communication System

University of Kansas17

Results – Round Trip TimeVariation of RTT

0

500

1000

1500

2000

2500

3000

3500

4000

1 6 11 16 21 26 31 36 41 46 51 56 61 66 71 76 81 86 91 96Time in sec

RT

T in

mse

c

Variation of RTT

0

1000

2000

3000

4000

5000

6000

7000

1 6 11 16 21 26 31 36 41 46 51 56 61 66 71 76 81 86 91 96

Time in sec

RTT

in m

sec

Round trip time during different times of the day

710608

748

1020

820 760920

1291 1232

1495

1952

14361244

801681

891

1304

995

587

1075930

0

500

1000

1500

2000

2500

8:40 9:02 10:34 10:34 11:45 11:56 12:45Time

RT

T in

mse

c

min avg mdev

Average RTT = 1.4 sec

Minimum observed RTT = 608 msec

Mean deviation = 800 msec

Detailed analysis in progress

Page 18: Multi-Link Iridium Satellite Data Communication System

University of Kansas18

Results – Reliability: 14th July 12-hr test

Uptime %

89

95

96

97

97

97

97

98

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

Page 19: Multi-Link Iridium Satellite Data Communication System

University of Kansas19

Results – Reliability: 22nd July 32-hr test

Uptime %

85

92

93

93

94

94

94

96

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

Page 20: Multi-Link Iridium Satellite Data Communication System

University of Kansas20

Results – Reliability: 19th July 6-hr test

Uptime %

67

81

85

85

85

85

85

90

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

Page 21: Multi-Link Iridium Satellite Data Communication System

University of Kansas21

Results – Mobile tests

Iridium system mounted in an autonomous vehicle (MARVIN)

Experiments monitored from another vehicle through 802.11b link

Iridium antennas

Page 22: Multi-Link Iridium Satellite Data Communication System

University of Kansas22

Results – Mobile tests

Uptime %

65

79

82

84

84

85

87

92

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

Page 23: Multi-Link Iridium Satellite Data Communication System

University of Kansas23

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

Page 24: Multi-Link Iridium Satellite Data Communication System

University of Kansas24

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.

Page 25: Multi-Link Iridium Satellite Data Communication System

University of Kansas25

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.

Page 26: Multi-Link Iridium Satellite Data Communication System

University of Kansas26

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

Page 27: Multi-Link Iridium Satellite Data Communication System

University of Kansas27

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.

Page 28: Multi-Link Iridium Satellite Data Communication System

University of Kansas28

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.

Page 29: Multi-Link Iridium Satellite Data Communication System

University of Kansas29

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.

Page 30: Multi-Link Iridium Satellite Data Communication System

University of Kansas30

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?