Data Centric, PositionBased Routing In Space Networks

1
Data Centric, Position-Based Routing In Space
Networks

• Siva Kumar Tanguturi Sanjaya Gajurel
• skt8, sxg125_at_eecs.case.edu
• 4/6/2005 EECS 600 Advanced Network Topics

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Agenda

• Introduction to Space Networks
• Background
• Architecture
• Implementation
• Simulation Experiments
• Conclusions
• Discussion

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This is Space

• Source Kul Bhasin, Jeff Hayden., Developing
  Architectures and Technologies for an Evolvable
  NASA Space Communication Infrastructure , 22nd
  AIAA International Communications Satellite
  Systems Conference, May 2004

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Space Networks

• Backbone or Inter-Planetary or Deep Space Network
• Earth-Mars Network
• Earth-Orbital Network
• Earth-Lagrangian-Relay-Orbital (Multi-Hop)
  Network
• Orbital Network
• Access Network
• Inter-spacecraft Intra-spacecraft Network
• Inter-Orbital
• Proximity Network or Surface Network
• Sensor Networks
• Inter-Surface Elements Networks (robots, access
  points, rovers, landers, balloons etc.
  communicating each other)
• Human-Robot Networks

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Communication Problems in Space

• Deep Space
• Very High and Variable Propagation Delay
• High Link Error Rates or Error-Prone Links
• Blackouts or Intermittent Connectivity
• Bandwidth Asymmetry
• Very Low Bandwidth/ Limited Link Capacity
• High Power Requirement
• Security
• Source http//www.jpl.nasa.gov/history/hires/1997
  /VLBI.jpg

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Communication Problems in Space

• Orbital
• Latency (Intermittent connection)
• Gravitational Fluctuations
• The Suns interference
• Dopplers effect in Satellite Radio Signal
• Orbital Debris
• Distributed Computation
• Source Kul Bhasin, Jeff Hayden., Space Internet
  Architectures and Technologies for NASA
  Enterprises.
• http//mrr.nrl.navy.mil/applications.html

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Communication Problems in Space

• Surface
• Noise Power issue
• Highly mobile
• Weight, Cost, Power
• Harsh Environment
• No infrastructure (Ad Hoc topology)
• Sourcehttp//scp.grc.nasa.gov/images/portfolio/pn
  /pn20main.jpg

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Agenda

• Introduction to Space Networks
• Background
• Architecture
• Implementation
• Simulation Experiments
• Conclusions
• Discussion

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Problems with existing TCP/IP protocol suite

• The current approaches cannot support the dynamic
  nature of the space networks.
• They work well only if the nodes and links are
  fixed and well-known ahead of time.
• They are not intelligent to discover the links as
  they become available and use them for routing.

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Effect of Space Environment on TCP

• Effect of Error Prone Links
• TCP is designed to handle packet loss by
  identifying and retransmitting lost segments
  assuming the source of all packet loss is network
  congestion
• Effect of Asymmetric Channels
• TCP rely on feedback in the form of cumulative
  acknowledgements from the receiver to ensure
  reliability. In addition, TCP is ack-clocked,
  relying on the timely arrival of
  acknowledgements, to make steady progress and
  fully utilize the available bandwidth of the
  path.

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Effect of Space Environment of TCP

• Effect of Limited Link Capacity
• The packet overhead, at least 20 bytes of TCP
  header per packet, can consume a sizable share of
  a limited bandwidth channel.
• Intermittent Connectivity
• Even short-term link outages pose a problem for
  TCP ranging from poor throughput in best case to
  an aborted connections in the worst case.
• Extremely long and variable Propagation Delays
• For the very long propagation delay in minutes,
  TCP has to set its retransmission timer very long
  to wait for the acknowledgement. This long delay
  is not acceptable. Moreover, because of the
  changing network topology, TCP cant estimates
  the optimal timeout.

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Effects of Space Environment on Network Layer

• Naming And Addressing
• If the application on a remote planet wished to
  resolve an earth-based address, the long
  round-trip delay to query the DNS is significant
  in terms of available communication time.
• With the use of secondary DNS on the surface,
  addresses updates have to be sent frequently to
  the secondary DNS that can consume a large
  portion of the limited bandwidth of the space.

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Effects of Space Environment on Routing

• Both MANET routing protocols and BGP/OSPF do not
  have mechanism to use periodicity of the links to
  compute paths.
• They use only the active links to compute a path
• They cannot adopt to network dynamics without
  requiring a manual intervention.
• Though they are known to be highly stable and
  scalable, they can not be directly used in the
  context of space networks.

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Approaches

• Data-Centric approach can be used to enable
  energy efficient and low latency operation in
  proximity networks.
• Position Based Routing approach can be
  efficiently used in the space orbital and
  backbone networks having predictable
  trajectories.

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Data-Centric Position-Based Routing Approach

• In Data Centric approach a message specifies its
  content in terms of attributes location,
  temperature and so on and there will be a
  in-networking processing of data.
• The Positional Link-trajectory State (PLS)
  Protocol that is used can get the link
  trajectories along with their metrics such as
  latency, data rate, error characteristics from
  STK (Satellite Tool Kit) to provide the future
  routing information. Each node calculates the
  shortest path and this information is
  disseminated throughout the space network.

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Agenda

• Introduction to Space Networks
• Background
• Architecture
• Implementation
• Simulation Experiments
• Conclusions
• Discussion

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ASCoT

• ASCoT Autonomous Space Communication Technology
• Is a routing and scheduling substrate for
  flexible tasking and coordination among space
  assets.
• Scalable
• Able to deal with message propagation latencies.
• Support connectivity changes
• Support Heterogeneous and asymmetric link
  bandwidths

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Assumption

• ASCoT expects the underlying system to provide a
  variety of information and services to the ASCoT
  middleware.
• This includes
• Navigation information
• characteristics of the links available and nodes
  on the other end, including position (current and
  expected), bandwidth, reliability, latency, etc.
• Current position of the node
• Local status
• power, health, load of transmission queues,etc.

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Data-Centric Approach

• Naming the data allows the system to eliminate
  different levels of binding
• Naming the data allows in-network processing of
  data.

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Data-Centric Approach

• Example
• Query for the average temperature of the shadowed
  parts in Gusev crater,
• Query can be flooded in the proximity network
• only the nodes that meet the query criteria (in
  Gusev crater and in shadowed parts) will respond
  to the query thereby avoiding multiple steps of
  binding and spending energy transmitting data
  from nodes that are not in the shadowed parts of
  the crater.
• Intermediate nodes also have the context to
  transform the data in several interesting Ways
• to aggregate different data items that perhaps
  have redundant information (e.g. temperature data
  from nearby sensors)
• reduce information in response to resource
  constraints (e.g. downsample an image because the
  image size exceeds available network capacity).

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Data-Centric Approach

• Used in Proximity Networks
• Energy Efficient
• Reduce the latency of communications

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Positioning Link-trajectory State (PLS)

• PLS is modified to the context of space networks.
• Each node independently computes shortest path
  tree using modified Dijkstras Algorithm, getting
  metrics like latency, data rate, and bit error
  rate (Satellite Tool Kit,STK).
• Unlike traditional Link-State Routing (LSR), the
  information disseminated throughout the network
  is the trajectory of nodes in space, and the
  availability of the link end-points now or in the
  future.

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PLS

• The PLS is only run in mobile space assets like
  satellites, moving base stations.
• PLS routing exchange information like
• u,p(u),v,t,metrics(u-gtv) which are flooded
  throughout the network.?
• Tradeoffs between frequency of information
  exchange and network resources (energy) as well
  as updates accumulation.
• Intelligent scheduling can be employed by which
  better links are waited for QoS.

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Key Components of ASCoT

• Link Information Dissemination
• Takes advantage of the space assets relative
  predictability by distributing information about
  link availability throughout the network ahead of
  time.
• Path Computation
• predicted link connectivity and time-varying
  graphs are taken into account for path
  computation.
• intelligent scheduling to meet the applications
  QoS requirement
• Message Forwarding
• once routing table is populated for a given
  metric, lookup the best next hop towards the
  destination and buffer the packet until the link
  becomes available.

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Message Switching

• The base station acts as a message gateway.
• It decodes the data-centric name for the target,
  encodes it as an attribute (say temperature)
  along with other constraints for the query.
• Diffusion Semantics is used to harvest data as
  follows
• A node translates the query into a interest
  message, floods the network sets up gradients
  (navigator) in the network.
• Nodes (sources) reply the query as
  attribute-value tuple and inject it into the
  network.
• Gradients now guide the data to the base station
  by matching attributes in the data message to
  that of the gradients established by the interest
  messages.

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Implementation Structure

• Web-Based Query Interface
• Implemented in OPNET
• Data taken from STK

Implementation in OPNET
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Implementation Structure

• ascot_app
• ascot_nav
• ascot_router
• position_manager
• Antenna modules

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Demonstrated ASCoT Features

• Its ability to deal with heterogeneous hardware.
  The Earth and Mars relay satellites, as well as
  the Mars base station, may utilize completely
  different transmission hardware. As long as they
  have a form of the IP stack and ASCoT running on
  top, the communication occurs seamlessly.
• The reliability of the protocol in the face of
  dynamic network topology, short link duration and
  long link latencies. As relay stations become
  occluded or occupied with tasks of higher
  priority (or orientation requirements force them
  to cut the current link), ASCoT automatically
  selects a different path that uses orbiters that
  become available.

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Demonstrated ASCoT Features

• PLS routing exploits future link information to
  predictively route on paths that become available
  just as the message travels along, and buffers
  messages as it waits for the links to come up if
  necessary.
• Automatic and efficient path discovery and link
  information distribution that allows PLS path
  computation to occur. Several parameters allow
  this behavior to be tuned to the current network
  state.

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Demonstrated ASCoT Features

• Source http//scp.grc.nasa.gov/images/portfolio/a
  n/an_3.jpg

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Simulation Components

• PI Specifies the source and the constraints of
  the data using a web interface.
• DSN (Deep Space Network) The Madrid DSN node
  participated in PLS.
• Earth Orbiters Six Middle Earth Orbit (MEO)
  satellites
• Mars Orbiters Three satellites in
  Aerosynchronous and five satellites in moderately
  inclined lower Mars orbit.
• Mars Base Station communication with rovers
  happen thorough base station
• Surface Rovers Spirit and Opportunity can
  communicate with base station.

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Simulation and Experiments (1)
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Simulation and Experiments (2)
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Simulation and Experiments (3)
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Conclusions

• ASCoT is a new data-centric and position-based
  routing architecture for future space science
  mission. The space missions involve large number
  of satellites and other nodes and the current
  static routing (manual ) is no more scalable.
• Data-centric approach avoids the traditional
  address-centric energy consuming approach to make
  up for the energy deprived space nodes.
• Planning to add design scheduling and resource
  allocation strategies.
• Even with the limited knowledge about the future
  available links, ASCoT can discover paths that
  can be used to forward message successfully and
  efficiently.

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Critiques

• This paper tries to solve the communication
  difficulties in space network by emphasizing the
  data-centric and position-based routing approach.
• The data to be communicated between the earth and
  the Mars is only the telemetry type. Also didnt
  address the issues of real time and bulk load
  (picture, video) data transfers.
• Direct communication facilities among the surface
  elements required for the space mission has not
  been mentioned.
• Using PLS, the router is queuing packet when the
  satellites get occluded but didnt mention how
  long. That can be hours and special store and
  forward router (used in DTN) may be required.

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Question Session

• Feel free to ask the doubts and questions. We
  will try to answer them ?
• Your comments are really appreciated
• Thank You