Research in Wireless Ad-Hoc Sensor Networks: Routing and data transport protocols

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Research in Wireless Ad-Hoc Sensor
NetworksRouting and data transport protocols

• Edo Biagioni
• presenting work done in collaboration with
• Kim Bridges and Brian Chee, and
• Shu Chen, Wei Chen, Lisa Fan, Dan Morton,
• Ben Roy, Yihua Xie
• April 23, 2004

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Wireless Ad-Hoc networks

• Each node has a radio transceiver
• Each node generates and receives data
• Each node must also transport data for other
  senders
• Node distribution is planned or random
• Some issues where to send data (routing)? how to
  send data efficiently?
• Could be mobile (MANet), fixed, or both

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Sensor Networks

• sensors are low-power (often battery powered),
  deployed for long periods in remote locations
• data can be retrieved manually, but it is better
  to do so automatically over a network
• some sensor networks might be very large, so
  scalability is an issue

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Ad-hoc Wireless Sensor Networks

• monitor remote sites over extended periods at low
  cost science, agriculture, tourism, military
  applications
• e.g. study endangered plants to find out why they
  are endangered

• e.g. monitor crops to determine when to water or
  apply fertilizer
• environmental monitoring, and also images, and
  intrusion or herbivore detection

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Mobile Ad-Hoc Networks

• Nodes are assumed to be moving continuously and
  at random
• must minimize routing overhead
• many protocols, including DSR, AODV
• few applications UAVs, vehicles
• little study (so far) on performance e.g.
  transmitting TCP content

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Challenges in WirelessAd-Hoc Sensor Networks

• make sense of large amounts of data
  visualization
• minimize the data transmitted model generation,
  distributed event detection

• conserve power, e.g. by sleeping
• re-route around nodes that have failed and nodes
  that are congested
• deal sanely with disconnection
• support encryption, heterogeneity

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Protocol Design

• efficient, reliable, high throughput, low delay
  (not unusual)
• low power requires low delay to completion (low
  packet delay and high throughput) and high
  efficiency (do not transmit unnecessary packets)
• low power also requires synchronization
• baseline is flooding broadcast

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Wireless Ad-Hoc Sensor Network Protocol Examples
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WSNs and MANets

• Wireless sensor network nodes are even lower
  power than MANet nodes
• nodes may be simpler than MANet nodes
• no motion (fixed) or limited motion
  (fixed-mobile)
• worth discovering and using good routes
• nodes may know position

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building an environmental sensor network PODS

• http//www.pods.hawaii.edu
• high resolution images
• sunlight, temperature, rain
• V0 wired sensor boards
• V1 PC-104, PC-compatibles running Linux, 802.11
  for communications, BasicStamp power control
  board
• V2 Compaq Ipaq, Linux, 802.11
• V3 in the planning stages

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Multipath On-Demand Routing

• Shu Chen
• protocol to carry IP packets
• establish routes on demand only send a
  broadcast, reply along the reverse path
• may be multiple routes to a destination using
  all of them in turn provides load balancing,
  redundancy, and reliability
• put routes on probation if they fail keep trying
  them for a little while

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MOR performance

• faster transmission of fixed payload (over TCP)
  than DSR, AODV
• multipath with reliability layer effectively
  routes around congestion
• podr long-term uninterrupted service in deployed
  pods, also works under ns-2
• hop-by-hop ack (e.g. 802.11) to decide whether to
  retransmit on this hop

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Lusus Protocol

• Dan Morton
• Really low power is only available on really
  simple processors such as PIC and AVR, with lt 1KB
  RAM, small programs
• Need a really simple protocol
• only send data (not IP)
• only send to nearest base station
• hop-by-hop, not end-to-end reliability
• short packets, very low overhead

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Lusus Techniques

• base stations regularly broadcast synchronization
  messages
• each retransmission increases the distance
• only send to nearest base station
• data from different sources may be combined
  enroute
• messages are retransmitted if there is no ack
  from the next hop
• implementation is in progress

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Sensor Network Data Transmission ProtocolSNDT

• Lisa Fan and Yihua Xie
• IP over MOR, can use ssh, but
• ssh has high overhead for small transfers
• want connectionless, secure, and efficient
  protocol
• use UDP, with explicit acks to minimize the
  overhead
• rate-limit transmission to avoid generating
  congestion

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SNDT security issues

• initial secret is part of a node config
• authentication to prevent bad data
• encryption data and commands should not be
  visible without the key
• initial secret is leveraged to exchange session
  keys
• nodes send data to base station
• base station sends commands and configuration to
  nodes

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SNDT open issues

• distributing time must be done quickly, but
  authentication takes time
• measuring RTT is hard if decryption is needed
  before ack
• each key must have an ID, which must be present
  on packets does this make the attacker's life
  easier?
• maintaining session keys, and recovering from
  reboots, can be challenging

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Distributed Route Table (DiRT)

• Ben Roy
• routing or forwarding to many hosts requires
  large routing tables
• distribute the routing tables so each node has at
  most O(log(N)) routes, yet every node can reach
  every other
• node IDs are set to be 0..N-1
• each node i has source routes for i1, i2, i4,
  i8, etc.

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DiRT routing

• for node i, if the destination D is in the
  routing table, send to it
• otherwise, compute ?D-i, the difference in
  addresses
• for each destination j in i's routing table, find
  the one with the smallest ?, (will have at least
  one) and send to that node
• packets require at most O(log(N)) legs, each of
  maximum length the diameter of the network

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Distributed Routing TablesOpen Issues

• Are there better ways to distribute large routing
  tables?
• for example, among neighbors
• if DiRT is used, what is the likelyhood of
  packets being rerouted along a better route
  encountered along the way?
• analysis how much better are we really doing
  than broadcast?
• how does network geometry affect that?

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Geographic Routing

• each node knows its own position, e.g. via GPS
• if the destination is identified by position,
  simply route to the neighbor nearest the
  destination
• can cause routing loops, e.g. at dead ends
• many refinements, but no good solutions

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Geometric Routing GEO

• geographic routing works fine as long as the
  network is densely connected
• only problems are at the edges of a connected
  area
• communicate the geometry of the connected areas,
  and route around any holes
• all the nodes on an edge must keep track of the
  geometry of that edge

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GEO implementation

• Wei Chen
• on the ns-2 simulator
• complex topologies simulated
• many nodes simulated
• scalability is good

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Related work

• Lots of protocols and ideas Berkeley motes,
  diffusion, Zigbee
• The Capacity of Wireless Networks, by Gupta and
  Kumar there are limits to how much we can send
• SPINS security protocols for sensor networks, by
  Perrig et al. --practical secure transmission on
  tiny processors
• http//www2.ics.hawaii.edu/esb/prof/pub/ijhpca02.
  html, Biagioni and Bridges

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Interesting Issues

• new network, e.g. IP assumptions don't work,
  connectivity may be intermittent, and it is OK to
  design from scratch
• low power operation is required, but there may be
  different ways to achieve it physical layer,
  data link, network layer
• should there ever be networks where data is
  unencrypted? How can automatic encryption be set
  up effectively?

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More issues

• Are there better ways of routing?
• Are there reasonable standard benchmarks for
  routing?
• Many problems to be solved power aware routing,
  position determination, optimal node placement,
  architecture, operating system (e.g. TinyOS),
  scheduling, etc

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Summary

• Protocols to support goals of sensor network
  deployment MOR, Lusus, SNDT, DiRT, GEO
• building actual sensor networks to evaluate and
  motivate the ideas