Deployed Internets in the Interplanetary Internet

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Deployed Internets in the Interplanetary Internet

• Robert C. Durst
• MITRE
• October 25. 1999

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What is a deployed internet in the IPN?

• We differentiate between the long-haul backbone
  and deployed networks that have round-trip time
  characteristics closer to those for which the
  Internet was designed
• Any network that has the following attributes is
  considered a deployed internet
• Is connected via interplanetary backbone to
  another network
• Has an environment that does not inherently
  preclude the use of (possibly enhanced) Internet
  protocols
• Uses the Domain Name space as a common means of
  referencing objects and systems across deployed
  internets

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Deployed Internets Have a Broad Range of
Possible Configurations

• A single lander with an IPN gateway to a (real or
  virtual) internal network
• Small number of cooperating robots on planetary
  surface (e.g. Single lander, single rover)
• Orbiter-to-surface communication and coordination
  (e.g. sample return recovery)
• Multiple beyond-line-of-sight missions connected
  by low-orbit communication satellites
• Planet-stationary satellites for relay and
  gateway functions
• Spacecraft on-board LANs
• The Earths Internet

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Some Functions of Deployed Internets

• Science Data and Telemetry Return
• Command and Control of In-Situ Elements
• Telescience/Virtual Presence
• Initially back-hauled to earth
• Secondarily, in support of robotic control of
  robotic exploration
• Finally, in support of human in situ control of
  robotic exploration

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Differences between IPN deployed internets and
the Terrestrial Internet
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Effects of these differences, by layerLayer 0
Not in the communication model

• Power availability affects all aspects of
  deployed internet operation
• Solar conversion is the primary power source for
  foreseeable future
• Example The average solar intensity in Mars
  orbit is 590 W/m2, compared with 1370 W/m2 in
  Earth orbit
• Surface-based solar panels are subject to
• Atmospheric dust limiting available solar energy
• Dust build-up on/erosion of solar panels,
  reducing effectiveness over time
• Location-based reductions in solar intensity
• Seasonal variations in solar intensity
• Efficiency of communication at all layers is
  required to offset the limitations of power
  availability

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The Good News Is ...

• Much of the ongoing work in mobile ad hoc
  networking is interesting, relevant, and timely

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Physical Layer

• Spectrum management
• Theres no FCC for deployed internets - spectrum
  coordination still necessary
• 400MHz very popular due to diffraction effects
  (facilitates some beyond-line-of-sight comm) and
  moderate free space losses
• Tracking antennas
• Need vibration-tolerant phased-array antennas for
  wideband communication to low-orbiting satellites
  from mobile nodes traversing rough terrain
  (albeit slowly) -- Potential contributions by
  LEO-constellation vendors to support on-the-move
  users

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Link Layer

• Management of very low signal-to-noise ratios is
  of significant importance
• Unclear what coding schemes are best
• Convolutional - limited delay
• Concatenated (e.g. Reed-Solomon) - clean or out
• Turbo Codes - operation in very low SNRs, but
  never quite clean, plus typically long code
  blocks
• Ability to apply different coding regime to
  packets based on their QOS requirements may
  become very important
• Resource reservation at MAC layer may be of
  significant importance
• Closed loop control of remote resources may
  require resource coordination at multiple layers,
  including interference avoidance at link layer

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Link Layer (Continued)

• Resource constrained environments require
  cooperation at all layers
• Link layer entities must sense their own status
  and signal it to upper layer entities for
  appropriate adaptation
• Link availability
• Link capacity and congestion status
• Current error conditions

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Network Layer

• Deployed internets will be comprised of fixed
  (e.g. landers) and mobile elements
• Mobile elements can be slow-movers
• Rovers
• Balloons
• Mobile elements can be fast-movers
• Low orbiters
• Powered Aircraft
• Routing protocols must be able to constitute and
  maintain an ad hoc network with all of these
  elements
• Must efficiently adapt to changes in available
  link resources -- vertical handoffs?
• Must propagate signals of current conditions
  issued by link layer elements

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Network Layer (Continued)

• Resource allocation in dynamic environment
• Integrated services model? With reservation range
  rather than fixed operating point (supports
  signaling from lower layers)
• Must adapt to changing conditions in link layer,
  and not over-allocate resources in some nodes
  when others cannot support
• Self configuration
• Address allocation and management in the absence
  of fixed infrastructure is required
• Potential requirement for self-organization into
  hierarchies as network expands or aggregates
  separate subnetworks
• Applicable technology currently being developed
  for sensor networks

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Transport Layer

• Participation in power-efficient communication
  schemes
• Need to carefully consider the trade-offs between
  coding at the link layer and retransmission at
  the transport layer to optimize use of overall
  communication resources - may dictate mixed-loss
  operation at transport
• Adaptation to changing network conditions
• May require QOS-responsive reliable transport
• Efficient accommodation of link outages
• Explicit congestion signaling and prompt response
• Robust error trend indication with appropriate
  response
• Data rate asymmetry in in-situ satellite
  communications
• Must be able to accommodate gt1001 asymmetries
• Without degrading use of the high-rate side
• While still performing useful functions on the 1
  side

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Application Layer

• Service location in mobile ad hoc networks
• Dynamic assignment of all system services
• Election of replacement system providers in the
  event of system failure or network partitioning
• Subject of ongoing, potentially relevant research
• Network management and control
• Need for efficiency and aggregation in
  limited-capacity mobile networks
• Mobile node health and status monitoring
• Preemptive maintenance
• Get it back to the barn for repairs