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GPS: Applications to Distributed Systems and Networks

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Title: GPS: Applications to Distributed Systems and Networks


1
GPS Applications to Distributed Systems and
Networks
  • Raj Jain The Ohio State UniversityColumbus, OH
    43220Jain_at_ACM.Org http//www.cse.ohio-state.edu/
    jain/

2
(No Transcript)
3
Overview
  • Principles of operation
  • Current applications
  • Potential applications
  • Obstacles
  • Current products and manufacturers

4
Executive Summary
  • Precise determination of location, velocity,
    direction, and time.
  • Price is falling rapidly and applications are
    growing
  • Goal was to survey current applications
  • Most efforts are in providing navigational
    guidance to drivers
  • Only two non-navigational applications
  • Identified many new applications of GPS for
    distributed computing and networking
  • A few obstacles to GPS deployment
  • Detailed lists of GPS products, addresses of
    manufacturers
  • Sources for further information

5
Introduction
  • Space-based radio positioning system
  • Provide
  • time
  • three-dimensional position
  • velocity
  • First conceived after the launch of Sputnik 1 in
    1957
  • Measuring the frequency shifts in the small
    bleeps ??Distance

6
Principles of Location Determination
  • Broadcast signals allow computing the distance
    from the satellite
  • Distance from one satellite ? Any point on the
    circle (sphere)
  • Distance from two satellites ? Two points
    (circle)Ridiculous answer can be eliminated
  • Distance from three satellites ? One point (two
    points)
  • Distance from four satellites ? One point

7
NAVSTAR
  • Constellation of 24 satellites (Three are spare)
  • Orbiting at a height of 10,900 nautical miles
  • Orbital period of 12 hours
  • Planned life span of 7.5 years
  • Orbits inclined 55 degrees to the equatorial
    plane
  • Provide a minimum of four satellites in good
    geometric positions
  • Up to 10 GPS satellites are usually seen
  • Each satellites carries several cesium clocks
  • Positional accuracy of 100 m, Timing accuracy of
    300 ns
  • Frequency accuracies of a few parts in 1012

8
NAVSTAR (Cont)
  • Two L band frequencies, L1 (1575.42 MHz) and L2
    (1227.6 MHz)
  • L1 carries a precise (P) code and a
    coarse/acquisition (C/A) code
  • L2 carries the P code
  • The P code is encrypted (also known as Y code)
  • Only the C/A code is available to civilian users
  • Space vehicle (SV) number Assigned in order of
    launch
  • Two services SPS and PPS

9
Standard Positioning Service (SPS)
  • Sandard level of positioning and timing accuracy
  • Available to any user on a continuous worldwide
    basis
  • 100 m horizontal accuracy
  • 156 meter vertical accuracy
  • 167 ns time accuracy

10
Precise Positioning Service (PPS)
  • Can only be accessed by authorized users with
    cryptographic equipment and keys
  • US and Allied military and approved civil users
  • Accuracy
  • 17.8 meter horizontal
  • 27.7 m vertical
  • 100 ns time

11
Selective Availability (SA)
  • Intentional degradation by DOD to limit accuracy
  • For non-US military and government users
  • Accuracy of C/A code reduced from 30 m to 100 m

12
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13
Differential GPS (DGPS)
  • Method of eliminating errors in a GPS receiver
  • Assumes most of the errors seen by GPS receivers
    are common errors
  • Caused by clock deviation, selective
    availability, drift from predicted orbits,
    multipath error, internal receiver noise and
    changing radio propagation conditions in the
    ionosphere
  • Use a base station with known location to
    determine error
  • Use the error to correct the location of rovers
  • Continuous broadcast ? real-time DGPS
  • Post-processing correction (Used in surveying)
  • Offers accuracies of few m

14
Accurate Time using GPS
  • GPS Time Within 1 ?s of UTC. Began on January
    6, 1980
  • No leap seconds ? Lags behind UTC
  • Constant offset of 19 s with the International
    Atomic Time
  • Time accuracy from GPS signals
  • Better than 340 ns (95 probability) using SPS
  • 100 ns using PPS
  • Inexpensive GPS receivers operating at known
    positions ? accuracy of about 0.1 ?s with only
    one satellite in view
  • With more sophisticated techniques, one ns is
    possible (globally)
  • Requires advanced preparation, coordination of
    the two sites and tracking of specific satellites
    during specific time periods

15
Accurate Time using GPS
  • Time accuracy from GPS signals
  • Better than 340 ns (95 probability) using SPS
  • 100 ns using PPS
  • Inexpensive GPS receivers operating at known
    positions ? accuracy of about 0.1 ?s with only
    one satellite in view
  • With more sophisticated techniques, one ns is
    possible (globally)
  • Requires advanced preparation, coordination of
    the two sites and tracking of specific satellites
    during specific time periods

16
Current Applications of GPS
  • Frequency Counters
  • Intelligent Vehicle Highway Systems (IVHS)
  • Car Navigation Systems
  • Geographic Information Systems (GIS)
  • Emergency Systems Backpacking
  • Aviation
  • GPS Aides for the Blind
  • Astronomical Telescope Pointing
  • Atmospheric Sounding using GPS Signals
  • Tracking of Wild Animals
  • Recorded Position Information
  • Airborne Gravimetry

17
Commercial Efforts
  • Trimble Bell Atlantic, Trimble IBM, PacTel
    Cellular Wireless Wireless Solutions Inc
  • Vehicle tracking and location devices
  • Ford
  • GPS based car alarms to locate stolen cars,
  • Traffic control, Vehicle tracking, Vehicle
    recovery, Navigation, Mapping
  • Avis Testing GPS in rental cars in NYC area
  • As a navigational aid
  • DeTeMobil
  • GPS receivers in all cars in Germany
  • Pay tolls using smart cards and GSM digital phone

18
Current Distributed Systems and Networking
Applications
  • Network delays in DA-30
  • SONET Synchronization

19
Network Delays
  • Wandel Goltermann Inc.
  • DA-30 Internetwork Analyzer uses GPS to make
    latency measurements between Ethernet LANs linked
    by a WAN
  • GPS boards lock into the GPS time signal
    broadcasts
  • S/W conducts latency trials
  • Accurate to within 150 ?s
  • Requires two kits priced at 6,750 each
  • Ref Government Computer News, March 21, 1994,
    vol. 13, no. 6, p.64.

20
SONET Clock Distribution
  • Multiple bit streams to a single network element
    ? Need synchronized clocks
  • CCITT Recommendation G.811 ? Long term frequency
    departure
  • Building Integrated Timing Supply (BITS) is
    Bellcore's clock-system specification ?
    Multi-level hierarchy
  • Stratum 1 (ST-1) is the highest quality clock
  • BITS allows LORAN/Rubidium ST1 clock systems
  • ATT's primary reference clock (PRC) uses GPS
    signals for long term timing accuracy
  • Rubidium oscillators provide short-term stability
  • Ref Telephony, August 24, 1992, pp. 50-54.

21
Potential Applications to Distributed Systems
and Networks
  • Time applications
  • Position Applications

22
Time Applications
  • Circuit Switching Using Synchronized Clocks
  • Synchronous Slotted Systems
  • Clock Synchronization in Distributed System
  • Database Synchronization
  • Connectionless Real-time Communication
  • Real-Time Communications
  • One-Way Delay
  • Delay based routing
  • Time to Live

23
Circuit Switching Using Synchronized Clocks
  • Synchronized clocks ? circuit switching easy
  • Precompute switching schedule
  • Similar to synchronized lights on roads

24
Synchronous Slotted Systems
  • Slotted systems are less sensitive to distance
    bandwidth product
  • More suitable for high speed or long distance
    networks
  • Slotted architectures for all-optical,
    multi-gigabit networks
  • Need clock synchronization
  • GPS clocks an all-optical ARPA research project

25
Clock Synchronization in Distributed System
  • Clock difference
  • Currently NTP, OSF-DTS, DECdts, Fuzzbal, timed
  • Future GPS clocks (1 ns) at least in timeservers
  • Ordering of events (e.g., FCFS scheduling)
  • Consistent update of replicated data
  • At most once receipt of messages
  • Authentication tickets in some systems (e.g.,
    Kerberos)
  • Ensuring atomicity
  • Expiration of privileges
  • Prearranged synchronization
  • Ordering multi-version objects

26
Database Synchronization
  • Synchronization after a failure or a disconnected
    operation
  • Use logs with timestamp to decide the order of
    actions
  • More precise clocks ? less conflicts

27
Connectionless Real-time Communication
  • Delay guarantees on IP-like networks ? Need
    deadline scheduling
  • GPS ? Deadline timestamp on the packet
  • Similarly, scheduling subtasks of real-time tasks

28
One-Way Delay
  • Currently, clock differences one-way
    delays??Can't measure one-way delay
  • Round-trip delays used instead
  • Example ATM networks ABR parameters are
    fn(delay)
  • GPS synchronized clocks at source and
    destination? exact one-way delay between source
    and destination and to every switch can be
    measured with a single timestamp.

29
Delay based routing
  • Internet uses link delays for routing
  • Accurate measurement is difficult ? approximate
    or round-trip delay used
  • GPS provided exact one-way delay can be used

30
Time to Live
  • Helps remove old packets from the networks
  • Currently, the time-to-live field is decremented
    by 500 ms regardless of actual delay
  • With GPS synchronized clock, exact time-to-live
    possible

31
Diagnostics/Maintenance of system clocks
  • A GPS frequency calibrator can be used to
    periodically check crystals in various equipment

32
Time and Frequency Alternatives
  • National Institute of Standards and Technology
    (NIST)
  • WWV and WWVH radio broadcasts (accurate to 1 ms)
  • WWWVB broadcasts (2 to 3 parts in 1011)
  • US Naval Observatory (USNO)
  • Loran-C (LOng RAnge Navigation)
  • Land based radio navigation system
  • Frequency accuracies of 1 part in 1012, Time
    better than 1 ?s
  • Both USNO and NIST provide
  • Telephone voice messages (accuracy 30 ms)
  • Computer modem time transfer (several ms)
  • Remote synchronization of time bases (10-9).

33
Position Applications
  • Resource Location
  • Location Adaptive Protocols
  • Handoffs in Wireless Networks
  • Prescheduled Hand-overs Based on Velocity and
    Direction
  • Adaptive Transmission Power Control Algorithm
  • Directional Antennas
  • Temporary Cell Partitioning for Congestion
    Avoidance
  • Peer-to-peer Routing with Limited Range Receivers
  • Email Delivery Based on Geographic Location
  • Distributed Robot Control and Navigation
  • Equipment Location Marking for Maintenance Crew

34
Resource Location
  • Digitized maps and GPS locations
  • Find the nearest printer or fileserver
  • Prescheduling possible

35
Location Adaptive Protocols
  • Currently, networking is location transparent
  • Service decisions do not use location
  • In many applications, knowing location helps
  • Examples Home vs Office vs Car. Electronic Fence.

36
Home vs Office vs Car
  • Different physical medium wire, ISDN, modem,
    cellular, or radio
  • Different bandwidth bandwidth, cost, and error
    characteristics
  • Mobile computing decisions fn(GPS
    location)Example Which files to fetch for home
    vs other town

37
Electronic Fence
  • Company confidential papers stay within physical
    walls
  • GPS provides electronic fence for electronic
    information
  • Information usable only if computer is within the
    corporate boundary

38
Handoffs in Wireless Networks
  • Inter-cell (change base) or intra-cell (change
    channel)
  • Decision by base or by mobile unit
  • Currently use signal strengthBetter to use
    position
  • Avoids passive listening to beacons
  • Simplifies handoff

39
Prescheduled Uninterrupted Handoffs
  • Signal strength ? Difficult to predict future
  • GPS location, velocity, and direction ? Future
    predictable
  • Handoff ? Interruption in service as the packets
    sent to the previous base have to be forwarded to
    the new base
  • Prediction ? Prenegotiate the hand-over with all
    parties

40
Adaptive Transmission Power Control Algorithm
  • Battery lifetime is important for mobile
    computing
  • Little hope for exponential increase in lifetime
  • Need to save battery usage
  • Optimize transmission power
  • Nearby base ? transmit less power
  • Also allow frequency reuse in the same cell

41
Directional Antennas
  • Transmission in all directions ? most of the
    energy wasted
  • GPS ? less power
  • Particularly helpful for satellite communication
  • Also allow better packing density - more users
    for the same space
  • Provides the minimum radiated RF pattern for
    covert communications.
  • Can talk to the least busy base unit even if it
    is not closest unit

42
Temporary Cell Partitioning for Congestion
Avoidance
  • Cell splitting Dividing a cell to form new cells
  • Allows reuse of spectrum and helps in reducing
    congestion
  • Requires prior preparation and usually a
    permanent change
  • GPS ? dynamic, quick, temporary splitting
    feasible
  • Can also be used in case of base station failures

43
Peer-to-peer Routing with Limited Range Receivers
  • Civilian wireless communication uses base units
  • Military communication ? no pre-existing
    infrastructure? Better to use peer-to-peer
    communication
  • Position, heading, velocity, as well as, digital
    terrain topology information can be used for
    optimum routing

44
Email Delivery Based on Geographic Location
  • Name, addresses, route, and physical position are
    not related
  • Multicast/anycast to a particular geographic
    location
  • For example, "to all police cars near Stanford
    university on route 101"

45
Distributed Robot Control and Navigation
  • Intelligent robots can use position and
    environment information
  • Unmanned vehicles can navigate effectively.

46
Equipment Location Marking for Maintenance Crew
  • Service requesters (mobile or stationary) provide
    GPS location
  • Maintenance crew carry GPS to locate the equipment

47
Current Limitations of GPS
  • Selective Availability degrades achievable
    accuracies
  • Temporary outage of the receiver as the receiver
    passes under obstructions? GPS for performance
    not for operation
  • Systems should continue to work without the GPS
  • Like cache memories

48
Details of Selected Products
  • Trimble's Mobile GPS Card Type II PCMCIA GPS
    sensor by Trimble (995). 3 channels tracking up
    to 8 satellites. 100 m accuracy. Acquisition time
    of less than 30 s and re-acquisition rate of 2-3
    s.
  • Trimble's Mobile GPS Gold Card
    Differential-ready (1,595). Provides 2-5 m
    accuracy in real-time.
  • Trimble's Mobile GPS Intelligent Sensor 100
    Low-end sensor 395
  • Rockwell's NavCard PCMCIA GPS sensor
  • Mobile Computing Kit Includes pen-based TelePad,
    Proxim's RangeLAN, cellular phone, Trimble GPS,
    FotoMan Plus camera, ScanMan, AudioMan (7,299).

49
GPS Software Applications
  • GPS for windows (1,995) By Peacock Systems
  • City Streets for Windows 99.95 by Road Scholar
    software
  • Streets on a Disk By Kylnas Engineering
    (22595/county)
  • Map'n'GO (50) 3CS Software.
  • NCompass 3.0 for Windows - real time GPS
  • Zagat-Axxis CityGuide by Axxis Software.
  • MapInfo for Windows 3.0 MapInfo Corp.
  • Atlas GIS for Windows 2.0 By Strategic Mapping
    Inc.
  • GISPlus for PC By Caliper Corp.
  • Maptech Professional Marine Chart S/W (1,290)
    by Resolution Mapping Inc.

50
Summary
  • Cheap PCMCIA receivers for 300-400 ? Growing
    applications
  • Currently mostly for navigational guidance to
    drivers
  • SONET and Wolter and Golderman's DA-30 network
    analyzer
  • Many many potential applications
  • Main obstacles Antennas must point to open sky

51
References Books
  • Jeff Hurn, Differential GPS Explained, Trimble
    Navigation, 1993.
  • Jeff Hurn, GPS A Guide to the Next Utility,
    Tremble Navigation, 1988.
  • David Wells et al., Guide to GPS Positioning
    (ISBN 0-920-114-73-3), Canadian Associates,
    1986.
  • Tom Logsdon, Navstar Global Positioning System,
    Van Nostrand Reinhold, 1992.
  • Hoffmann-Wellenhof, et al, Global Positioning
    System, Theory and Practice, 3rd Edition,
    Springer-Verlag.
  • Ackroyd and Robert Lorimer, Global Navigation-A
    GPS users guide, 2nd Edition, Loyds of London,
    1994.

52
References On-Line
  • Michael Heflin, Global GPS Time Series.''
    http//sideshow.jpl.nasa.gov/mbh/series.html
  • Peter H. Dana, An Overview of the Global
    Positioning System (GPS),'' http//wwwhost.cc.utex
    as.edu/ftp/pub/grg/gcraft/notes/gps/gps.html
  • Hal Mueller, Hal Mueller's GPS Sources,''
    http//www.zilker.net/hal/geoscience/gps.html
  • John T. Beadles, Introduction to GPS
    Applications,'' http//www.einet.net/editors/john-
    beadles/introgps.htm

53
ThankYou!
54
GPS Standards
  • NMEA-0183 Data format standard for
    communications between ship-borne navigationGPS
    receivers output this format but do not accept
    it.
  • RTCM-104 Radio Technical Commission for Maritime
    (RTCM) Services standard for DGPS
    operation.Version 2 used by many beacon systems
    (including the US Coast Guard system)Version 2.1
    includes additional information for the transfer
    of real-time kinematic data

55
Other Radio Navigation Systems
  • GLONASS Russian 24 satellites
  • LORAN-C LOng RAnge Navigation
  • TRANSIT First satellite system
  • Timation
  • Low-Altitude Satellites

56
LOng-RAnge Navigation (LORAN-C)
  • Ground-based radio navigation
  • Two versions
  • Loran C for civilian users
  • Loran D for military
  • A master and up to four secondary transmitting
    stations
  • Radio pulses centered on 100 kHz
  • Difference in arrival time ? position
  • Range Over 1500 kilom from master stations
  • Accuracy 100 to 500 m
  • Better than 30 m on shorter range

57
GLONASS
  • Russian
  • 24 satellites
  • Precise (P) code and a coarse/acquisition (C/A)
    code
  • P code is encrypted for military use
  • C/A code is available for civilian use

58
TRANSIT
  • First operational satellite navigation system
  • Developed by the Johns Hopkins Applied Physics
    Laboratory
  • Used Doppler shift of a radio signal transmitted
    from the satellite
  • Limitations
  • Two dimensional
  • Mutual interference ? Max five satellites
  • Satellites visible for only limited periods of
    time

59
Timation
  • Developed in 1972 by the Naval Research
    Laboratory (NRL)
  • Satellites intended to provide time and frequency
    information
  • Initially used quartz crystal oscillators
  • Later atomic clocks
  • Acted as a GPS technology demonstrator.

60
Low-altitude Satellites
  • Experiments are also being
  • Poposals to place GPS tansmitters on low altitude
    satellites
  • Would greatly reduce the cost

61
Time Synchronization Techniques
  • Absolute time synchronization
  • Receiver picks up the signals from a single GPS
    satellite
  • Accuracies of about 100 ns (with S/A off) and 300
    ns (with S/A on)
  • Clock fly-over
  • Satellite swings up over two sites
  • Yields a clock synchronization error of around 50
    ns
  • Common view mode
  • Two distant sites have line-of-site to the same
    satellite at the same time.
  • Yields synchronization errors of 10 ns or less
  • Multi-satellite common view mode
  • Four or more satellites that are being observed
    simultaneously from the two different clock sites
  • Can achieve synchronization errors as small as 1
    ns

62
Frequency Counters
  • Accurate frequency counters, time interval
    counters, frequency calibrators and phase
    comparators can be built using the GPS technology
  • GPS clock module Stellar GPS Corp (now
    Absolute Time Corp)
  • L1 C/A GPS receiver optimized for frequency and
    time
  • Provides a stable 10 MHz reference frequency
  • RMS pulse-to-pulse jitter of 1 ns for 1 pps
    output
  • Frequency/timing offset measurements (timing
    resolution is 5 ns and frequency resolution of
    10-12

63
Intelligent Vehicle Highway Systems (IVHS)
  • To improve highway safety
  • Ease traffic congestion
  • Reduce harmful environmental effects

64
Car Navigation Systems
  • GPS receiver digital maps
  • Provides location and directions

65
Geographic Information Systems (GIS)
  • GPS receiver Digital maps Cellular networks
  • Permit state and local governments
  • Efficiently coordinate roadway maintenance and
    construction in rural areas
  • Provide efficient ways of maintaining roadway
    databases
  • Maintain accident inventories

66
Emergency Systems
  • Emergency system communicates the position to the
    base
  • car alarms with GPS to locate stolen cars

67
Aviation
  • Aircraft safety systems
  • Air traffic control
  • Can plot aircraft altitude to a pitch of 0.1
    degree
  • Zero visibility landing
  • Will reduce the manpower in the control tower and
    cockpit

68
GPS Aides for the Blind
  • Real time GPS along with digitized maps and audio
    capability
  • To provide useful navigational capabilities

69
Astronomical Telescope Pointing
  • Observe the occultation of stars by asteroids
  • To determine the sizes and shapes of asteroids
  • Need mobile telescopes placed in the predicted
    path of the shadow
  • Odetics GPStar 325 receiver feeds coordinates to
    a computer
  • Timing signals are used to time the event
  • Ref Mark Trueblood In the Shadow of the
    Asteroid,'' GPS World Vol 4, no. 11, November
    1993, pp. 22-30.

70
Atmospheric Sounding using GPS Signals
  • Observe planetary atmospheres
  • Mariner and Voyager's radio signals transected a
    planets atmosphere
  • Detected phase changes in the radio signals
  • Can estimate atmospheric refractivity, density,
    pressure temperature and humidity.

71
Tracking of Wild Animals
  • To track animals and for studying their nomadic
    patterns
  • Animals are equipped with GPS receivers and with
    wireless transmitters
  • Position is transmitted to the control station

72
Recorded Position Information
  • To track executives
  • To determine charges (highway toll)
  • To search for stolen items (cars)
  • To study the migratory patterns (animals)
  • To validate legal claims

73
Airborne Gravimetry
  • To accurately position airplanes in flight
  • Its vertical acceleration and tilt can be
    monitored with GPS
  • Airborne gravimetric data can be used for natural
    resource exploration

74
Other Uses
  • Surveying
  • Navigation of missiles
  • Electric power synchronization
  • Census taking
  • Backpacking emergency systems
  • Natural resource management

75
Commercial Efforts (Cont)
  • Seiko Communications
  • Global wireless information services using FM
    radio.
  • Includes differential GPS data.
  • Fujitsu
  • The Car Marty vehicle multimedia device (2,640),
  • Consists of a system box, a CD player, and a 5.6"
    color TV
  • Sony Mobile Electronics and Etak Inc.
  • Computerized navigation system for automobiles
    (2,200)
  • PCMCIA GPS receiver on laptop computers
  • Info on restaurants, hotels, entertainment and
    shopping
  • Includes a CD-ROM (for map), a GPS antenna, a 5"
    color LCD display

76
Commercial Efforts (Cont)
  • Toshiba Developed a portable navigation system
  • Tusk Inc Tusk 386 - an all terrain supertablet
    pen computer with GPS.
  • Penstuff Trimble Navigation
  • Combine GPS technology with pen computers
  • Developed GPS standard for PenPoint
  • Record location in terms of latitude, longitude
    and altitude
  • Motorola
  • Cellular Positioning Emergency Messaging Unit
  • Communicates GPS-determined vehicle position and
    status
  • Also traxar Hand-held navigational computer.

77
TrueClock
  • Marketing term like ATT's True Voice''
  • Products implementing GPS clock marked True
    Clock''

78
GPS Products and Services
  • 200 million (sold) in 1992. Could reach 500M in
    1995
  • Include receivers, modems, simulators, range
    finders, robotic systems, and navigation modules.
  • GPS Receivers and Stations
  • Land Vehicle Receivers
  • Mapping Receivers
  • Aircraft Receivers
  • Miscellaneous Receivers
  • OEM receivers
  • PC Card (PCMCIA) Receivers
  • Shipboard Receivers

79
Products (cont)
  • Spacecraft Receivers
  • Surveying Receivers
  • Timing Receivers
  • Modems
  • Satellite Simulators
  • Laser Range Finders
  • Robotic Total Stations
  • Navigation Modules
  • Scientific GPS Software Suites
  • DGPS Correction Signal Services
  • Addresses of GPS Equipment Manufacturers. See
    report.

80
GPS S/W (Cont)
  • GPSez and GPSpac for Windows (1,290) by General
    Engineering and Systems S.A.
  • GPS MapKit XV By DeLorme Mapping. It links GPS
    to maps.
  • GPS Signal Simulation software Accord Software
    and Systems. (495). Platform to experiment with
    various modules of signal processing section of a
    GPS receiver.
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