Deep Space Networks

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InterPlanetary InternetDeep Space Network

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InterPlaNetary Internet Architecture

• InterPlaNetary Backbone Network
• InterPlaNetary External Network
• PlaNetary Network

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PlaNetary Network Architecture

• PlaNetary Satellite Network
• PlaNetary Surface Network

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CHALLENGES

• Extremely long and variable propagation delays
• Asymmetrical forward and reverse link capacities
• Extremely high link error rates
• Intermittent link connectivity, e.g., Blackouts
• Lack of fixed communication infrastructure
• Effects of planetary distances on the signal
  strength and the protocol design
• Power, mass, size, and cost constraints for
  communication hardware and protocol design
• Backward compatibility requirement due to high
  cost involved in deployment and launching
  processes

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Planned InterPlaNetary Internet Missions
Mission Name Schedule Description/Objective
Galaxy Evolution Explorer 2003 To measure star formation 11 billion years ago with UV wavelengths.
Rosetta February 2004 Comet orbiter and lander to gather scientific data.
Messenger March 2004 To study the characteristics of Mercury, and to search for water ice and other frozen volatiles.
Deep Impact December 2004 To investigate the interior of the comet, the crater formation process, the resulting crater, and any outgassing from the nucleus.
Mars Reconnaissance Orbiter July 2005 To study Mars from orbit, perform high-resolution measurements and serve as communications relay for later Mars landers until 2010.
Venus Express November 2005 To study the atmosphere and plasma environment of Venus.
New Horizons January 2006 To fly by Pluto and its moon Charon and return scientific data/images.
Dawn May 2006 To study two of the largest asteroids, Ceres and Vesta.
Kepler October 2006 Search for terrestrial planets, i.e., similar to Earth.
Europa Orbiter 2008 To study the Jupiters Moon Europas icy surface.
LISA 2007 To probe the gravity waves emitted by dwarf stars and other objects sucked into black holes.
Mars 2007 Late 2007 To launch a remote sensing orbiter and four small Netlanders to Mars.
Mars 2009 Late 2009 Smart Lander, Long Range Rover and Communication Satellite.
BepiColombo January 2011 To study Mercurys form, interior structure, geology, composition, etc.
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Proposed Consultative Committee for Space Data
Systems (CCSDS) Protocol Stack
for Mars Exploration Mission Communications
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Proposed Delay Tolerant Networking (DTN) Protocol
Stack
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Transport Layer Issues

• Extremely High Propagation Delays
• High Link Error Rates
• Asymmetrical Bandwidth
• Blackouts

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Extremely Long Propagation Delays
Planet RTTmin RTTmax
Mercury 1.1 30.2
Venus 5.6 35.8
Mars 9 55
Jupiter 81.6 133.3
Saturn 165.3 228.4
Uranus 356.9 435.6
Neptune 594.9 646.7
Pluto 593.3 1044.4
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Performance of Existing TCP Protocols

• Window-Based TCPs are not suitable!!!
• For RTT 40 min ? 20B/s throughput on 1Mb/s
  link !!

O. B. Akan, J. Fang, I. F. Akyildiz, Performance
of TCP Protocols in Deep Space Communication
Networks, IEEE Communications Letters, Vol. 6,
No. 11, pp. 478-480, November 2002.
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Space Communications Protocol Standards
Transport Protocol (SCPS-TP)

• Addresses link errors, asymmetry, and outages
• SCPS-TP Combination of existing TCP protocols
• Window-based
• Slow Start
• Retransmission timeout
• TCP-Vegas congestion control scheme variation
  of the RTT value as an indication of congestion
• SCPS-TP Rate-Based
• Does not perform congestion control
• Uses fixed transmission rate

New Transport Protocols are needed !!!
Space Communications Protocol
Specification-Transport Protocol (SCPS-TP)",
Recommendation for Space Data Systems Standards,
CCSDS 714.0-B-1, May 1999.
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TP-PlanetO. B. Akan, J. Fang and I.F.
Akyildiz, TP-Planet A Reliable Transport
Protocol for InterPlaNetary Internet, to appear
in IEEE Journal of Selected Areas in
Communications (JSAC), early 2004.
Steady State
t2RTT
Initial State
tRTT
Immediate Start
FollowUP
Follow Up

• Objective To address challenges of
  InterPlaNetary Internet
• A New Initial State Algorithm
• A New Congestion Detection Algorithm in Steady
  State
• A New Rate-Based scheme instead of Window-Based

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Multimedia Transport in InterPlaNetary Internet

• Additional Challenges
• Bounded Jitter
• Minimum Bandwidth
• Smoothness
• Error Control

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RCP-Planet OverviewJ. Fang and I.F. Akyildiz,
RCP Planet A Rate Control Scheme for
Multimedia Traffic in InterPlaNetary Internet,
July 2003.

• Objective To Address the Challenges
• Framework
• A New Packet Level FEC
• A New Rate-Based Approach
• A New BEGIN State Algorithm
• A New Rate Control Algorithm in
  OPERATIONAL State

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Transport LayerOpen Research Issues

• End-to-End Transport
• Feasibility of the end-to-end transport should be
  investigated and new end-to-end transport
  protocols should be devised accordingly.
• Extreme PlaNetary Distances
• Deep Space links with extreme delays such as
  Jupiter, Pluto have intermittent connectivity
  even within an RTT.
• Cross-layer Optimization
• The interactions between the transport layer and
  lower/higher layers should be maximized to
  increase network efficiency for scarce space link
  resources.

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Network Layer Issues

• Naming and Addressing
• in the InterPlaNetary Internet
• Routing
• in the InterPlaNetary Backbone Network
• Routing
• in PlaNetary Networks

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Naming and Addressing

• Purpose To provide inter-operability between
  different elements in the architecture
• Influencing Factors
• What objects are named?
• (Typically nodes or data objects)
• Whether a name can be directly used by a data
  router in order to determine the delivery path?
• The method by which name/object binding is
  managed?

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Domain Name System (DNS) Approach in Internet

• If an application on a remote planet needs to
  resolve an Earth based name to an address
• Problems
• If query an Earth-resident name server
• A significant delay of a round-trip time in
  the commencement of communication
• If maintain a secondary name server locally
  State updates would dominate communication
  channel utilization
• If maintain a static list of host names and
  addresses
• Not scale well with systems growth

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Tiered Naming and Addressing

• Name Tuple region ID, entity ID
• Region ID identifies the entitys region and is
  known by all regions in the InterPlaNetary
  Internet
• Entity ID is a name local to its entitys local
  region and treated as opaque data outside this
  region
• ? The opacity of entity names outside their local
  region
• enforces Late Binding the entity ID of a
  tuple is not interpreted outside its
  local region
• which avoids a universal name-to-address
  binding space and preserves a significant amount
  of autonomy within each region.

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An InterPlaNetary Internet Example and Host Name
Tuples
Host IPN regions Host name tuples
SRC earth.sol earth.sol, src.jpl.nasa.gov6769
GW1 earth.sol ipn.sol earth.sol, ipngw1.jpl.nasa.gov6769 ipn.sol, ipngw1.jpl.nasa.gov6769
GW2 ipn.sol mars.sol ipn.sol, ipngw2.jpl.nasa.gov6769 mars.sol, ipngw2.jpl.nasa.gov6769
DST mars.sol mars.sol, dst.jpl.nasa.gov6769
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ChallengesNetwork Layer

• Long and Variable Delays
• Without timely distribution of topology
  information, routing computations fail to
  converge to a common solution, resulting in route
  inconsistency or oscillation
• The node movement adds to the variability of
  delays
• Intermittent Connectivity
• Determine the predicted time and duration of
  intermittent links and the degree of uncertainity
• Obtain knowledge of the state of pending messages
• Schedule transmission of the pending messages
  when links become available
• SCPS-NP ? possible solution???

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Open Research IssuesNetwork Layer

• Distribution of Topology Information
• Combination of link state and distance vector
  information exchange
• Distribution of trajectory and velocity
  information
• Path Calculation
• Hop-by-hop routing is expected using incomplete
  topology information and probabilistic estimation
• Adaptive algorithms are needed for rerouting and
  caching decisions
• Interaction with Transport Layer Protocols

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ChallengesNetwork Layer (Planet)

• Extreme Power Constraints
• Space elements mainly depend on rechargeable
  battery using solar energy
• Frequent Network Partitioning
• The network can be partitioned due to harsh
  environmental factors
• Adaptive Routing through Heterogeneous Networks
• Fixed elements (e.g., landers)
• Satellites with scheduled movement
• Mobile elements with slow movement (e.g., rovers)
• Mobile elements with fast movement (e.g.,
  spacecraft)
• Low-power sensor nodes in clusters

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Medium Access Control InterPlaNetary Backbone
Network

• Challenges
• Very Long Propagation Delays
• Physical Design Change Constraints
• Topological Changes
• Power Constraints

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Medium Access Control InterPlaNetary Backbone
Network

• Vastly unexplored research field
• The suitability and performance evaluation of
  fundamental MAC schemes, i.e., TDMA, CDMA, and
  FDMA, should be investigated
• Thus far, Packet Telecommand, and Packet
  Telemetry standards developed by CCSDS are used
  to address deep space link layer issues
• (Virtual Channelization method!!!)

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Error ControlInterPlaNetary Backbone Network

• Deep space channel is generally modelled as
  Additive White Gaussian Noise (AWGN) channel
• Scientific space missions require bit-error rate
  of 10-5 or better after physical link layer
  coding
• ? Error control at link layer is necessary

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Error ControlInterPlaNetary Backbone Network

• CCSDS Telemetry Standard (Telemetry Channel
  Coding)
• For Gaussian Channels ?
• ½ Rate Convolutional Code
• For Bandwidth-Constrained Channels ?
• Punctured Convolutional Codes
• For Further Constrained Channels ?
• Concatenated Codes (i.e.,Convolutional code as
  the inner code and the RS code as the outer code)
• Own Experience ? TORNADO CODES!!!

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Error ControlInterPlaNetary Backbone Network

• Advance Orbiting Systems Rec. by CCSDS ?
• Space Link (ARQ) Protocol (SLAP)
• Packet Telecommand Standard of CCSDS ?
• Command Operation Procedure (COP) (GoBack
  N)

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Open Research IssuesLink Layer

• MAC for InterPlaNetary Backbone Network
• MAC for PlaNetary Networks
• Error Coding Schemes
• Cross-layer Optimization
• Optimum Packet Sizes

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Physical Layer Issues InterPlaNetary Backbone
Network

• Possible approach is to increase radiated RF
  signal energy
• Use of high power amplifiers such as travelling
  wave tubes (TWT) or klystrons which can produce
  output powers up to several thousand watts
• This comes with an expense of increased antenna
  size, cost and also power problems at remote
  nodes
• Current NASA DSN has several 70m antennas for
  deep space missions
• DSN operates in S-Band and X-Band (2GHz and 8GHz,
  respectively) for spacecraft telemetry, tracking
  and command
• Not adequate to reach high data rates aimed for
  InterPlaNetary Internet
• New 34m antennas are being developed to operate
  in Ka-Band (32 GHz) which will significantly
  improve data rates

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Open Research IssuesPHYSICAL LAYER

• Signal Power Loss
• Powerful and size-, mass-, and cost-efficient
  antennas and power amplifiers need to be
  developed
• Channel Coding
• Efficient and powerful channel coding schemes
  should be investigated to achieve reliable and
  very high rate bit delivery over the long delay
  InterPlaNetary Backbone links
• Optical Communications
• Optical communication technologies should be
  investigated for possible deployment in
  InterPlaNetary Backbone links
• Hardware Design
• Low-power low-cost transceiver and antennas
  should be developed
• Modulation Schemes
• Simple and low-power modulation schemes should be
  developed for PlaNetary Surface Network nodes.
  Ultra-wide Band (UWB) could be explored for this
  purpose

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Challenges in Deep Space Time Synchronization

• Variable and long transmission delays
• The long and variable delays may cause a
  fluctuating offset to the clock
• Variable transmission speed
• It may produce a fluctuating offset problem
• Variable temperature
• It may cause the clock to drift in different rate
• Variable electromagnetic interference
• This may cause the clock to drift or even
  permanent damage to the crystal if the equipment
  is not properly shielded

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Challenges in Deep Space Time Synchronization
(contd)

• Intermittent connectivity
• The situation may cause the clock offset to
  fluctuate and jump
• Impractical transmissions
• A time synchronization protocol can not depend on
  message retransmissions to synchronize the
  clocks, because the distance between deep space
  equipments are simply too large
• Distributed time servers
• Deep space equipments may require to synchronize
  to their local time servers, and the time servers
  have to synchronize among themselves

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Related Work

• Network Time Protocol
• Can not handle mobile servers and clients
  (variable range and range rate with intermittent
  connectivity)
• Has time offset wiggles of few milliseconds of
  amplitude
• DSN Frequency and Time Subsystems
• Uses several atomic frequency standards to
  synchronize the devices and provide references
  for the three DSN sites, i.e., Goldstone, USA
  Madrid, Spain Canberra, Australia
• Recommendation for proximity-1 space link
  protocol
• Finds the correlation between the clocks of
  proximity nodes. The correlation data and UTC
  time are used to correct the past and project the
  future UTC values

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Conclusions

• InterPlaNetary Internet will be the Internet of
  next generation deep space networks.
• There exist many significant challenges for the
  realization of InterPlaNetary Internet.
• Many researchers are currently engaged in
  developing the required technologies for this
  objective.

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FiNAL WORDS

• NASAs VISION
• to improve life here, to extend life to there,
  to find
• life beyond...
• NASAs MISSION
• to understand and protect our home planet, to
  explore
• the Universe and search for life, to inspire
• the next generation of explorers
• OUR AIM
• to point out the research problems and
  inspire the
• researchers worldwide to realize these
  objectives!!!!!!!!!