ESE680: Wireless Sensor Networks

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ESE680 Wireless Sensor Networks Special Topics
in Embedded Systems
Routing Lecture 7 Prof. Rahul Mangharam
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Administrivia

• Lab 2
• Due on Thursday, Feb 19 at 6pm
• Demo on Friday to Miroslav
• Lab 3
• Final labbefore main project
• Out today and Due on Mar 3 (you have 2 weekends)
• Reading Assignment 3
• Routing Protocols (on BlackBoard)
• Only review Rumor Routing the other handout is
  for reference
• Out today, summary due on Tue, Feb 26

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Outline of Previous Lecture

• Fundamentals of RF communications
• Basic concepts
• Modulation techniques
• 802.15 Standard
• Overview
• Physical Layer of 802.15.4

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Outline of Todays Lecture

• Purpose of routing
• Routing tables
• Construction and Maintenance
• Well-known Routing Protocols

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WSN Routing

• Ad hoc network
• Multi-hop network
• Routing Tables

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Routing Tables (1 of 2)
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Routing Tables (2 of 2)
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Characteristics of Routing in WSN

• Distributed
• Efficient (low overhead)
• Self-configuring
• Resilient (to changing network topology)

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Protocol Classification

• Table-driven or proactive
• Conservative try to keep accurate information
• On-demand

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Other Characteristics

• Energy-harvesting
• Energy-efficient
• Power-down to save energy
• Multiple paths
• Redundancy
• Load balancing
• Spread energy usage evenly

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Forwarding and Routing

• Flooding
• Only packets not seen earlier are forwarded
• TTL (Time-To-Live) to handle unreachable nodes
• Gossip
• Each node forwards a message with some
  probability
• Controlled Flooding
• Combination of Flooding and Gossip

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Gossiping and Unicast Forwarding

• Gossiping
• How do you select neighbors?
• Unicast Forwarding
• Wireless multicast advantage

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Gossiping Techniques

• Randomized forwarding
• Random walks
• Rumor routing
• Probabilistically and periodically forward
  messages
• Random walks with known destination
• Nodes get turned on and off to spread the load
• Rectangular grid of nodes
• Source in upper left corner
• Destination in lower right corner

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Energy-Efficient Unicast

• Assign cost value reflecting energy consumption
• Pick an algorithm to compute the least-cost paths
• How do you define an energy-efficient path
• Minimize energy per packet
• Long hops cost more, so minimum hopcount is not
  sufficient
• Maximize network lifetime
• Routing considering available battery energy
• Minimum total transmission power routing (MTPR)

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Minimize Energy Per Packet

• Minimize total energy required to transport
  packet by selecting a good route
• Minimum hop count _______
• Minimum energy route _______

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Maximize Network Lifetime

• Time until the first node fails
• Loss of coverage at a spot
• Network partition
• The energy of nodes at ends of minimum cut-set
  are critical

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Routing considering Battery Life

• Maximum total available battery capacity
• Maximize sum of available energy along path
• Minimum battery-cost routing (MBCR)
• Minimize the sum of reciprocals of battery energy
• Min-Max battery-cost routing (MMBCR)
• Minimum of the maximum value of reciprocal

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Example Unicast Protocols

• Attracting routes by re-directing
• Eavesdrop, interject oneself into route if it
  saves energy
• Distance vector routing over topology control
• Shortest path algorithms from a single source
• Max time to first node outage as a flow problem
• Find assignments of flows to nodes/paths to
  maximize time of first outage
• Max time to first node outage by max-min
  optimization
• Maximizing total number of messages that can be
  sent
• Re-computing routing tables is a burden

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Multi-path Unicast Routing

• Construct multiple paths between a source and a
  destination.
• Balance energy consumption
• Redundancy
• Sequential Assignment Routing (SAR)
• Construct trees outward from each sink neighbor
• Constructing energy-efficient secondary paths
• Braided paths to avoid large detours
• Simultaneous transmission over multiple paths
• Randomly choice of one of several paths

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Broadcast and Multicast

• Source-based tree
• Tree for each source to all destinations
• Minimize total cost of all links in tree (Steiner
  tree)
• Minimize the maximum cost to each destination
• Shared, core-based tree
• Single tree
• If destination sets for all sources are identical
• Mesh
• More complicated forwarding structures
• Remember Wireless Multicast Advantage

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Broadcast Incremental Power (BIP)

• Exploits wireless multicast advantage
• A node already transmitting to another node
  raises its transmission power to provide data to
  nodes farther away
• Additional cost
• Difference between current and higher power
• Saves cost for another transmission

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BIP Algorithm
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Geographic Routing

• Some applications require physical locations of
  nodes.
• Geo-casting sending messages to arbitrary nodes
  in a given region
• Not necessarily precise locations, but relatively
  close
• Position information can help in routing
• Small or non-existing routing tables
• Position-based routing

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Position-based Routing

• Simple and greedy geographic forwarding
• Minimize distance to destination in each step
• Nearest with forward progress
• Send to nearest neighbor which gets closer to
  destination
• Directional routing
• Emphasize direction rather than distance
• The problem of dead ends

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Recovery from Greedy Routing

• Right-hand rule to recover from greedy routing
• Greedy Perimeter Stateless Routing (GPSR)
• Combine Greedy and Face routing

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Routing Protocols

• Mobile Ad Hoc Networks working group (MANET) of
  IETF
• Protocols
• Destination Sequenced Distance Vector (DSDV)
• Temporally-Ordered Routing Algorithm (TORA
• Global State Routing (GSR)
• Ad hoc On-demand Distance Vector (AODV)
• Dynamic Source Routing (DSR)
• Label-Switched Routing (LSR)

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Dynamic Source Routing

• Completely self-configuring network
• Trivial loop-free routing
• Intermediate nodes do not need to be up-to-date
• Allows caching of routing information
• Two needed mechanisms
• Route discovery
• Route maintenance

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Route Discovery

• Search for destination in cache
• If not found, broadcast ROUTE_REQUEST
• Contains unique request ID
• Identifies initiator and target
• Record listing of intermediate nodes
• Target returns ROUTE_REPLY
• Initiator gets the reply and caches the route
• Can be uni-directional

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Route Discovery

• Example Node A is the initiator, and node E is
  the target.

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Route Discovery Limitation
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Route Maintenance

• Each intermediate node is responsible for
  confirming that the packet reached its next hop
• Return ROUTE_ERROR to sender if failed
• Sender removes this route from cache
• Proceeds with an alternate route, or
• Performs a Route Discovery

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Additional Route Discovery Features

• Caching overheard routing information
• Replying to ROUTE_REQUEST using cached routes
• ROUTE_REQUEST hop limits
• Preventing ROUTE_REPLY storms

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ROUTE_REPLY Storm
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Route Maintenance Features

• Packet salvaging
• Increased spreading of ROUTE_ERROR messages
• Caching negative information
• Automatic route shortening
• Subsequent intermediary sends ROUTE_REPLY

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Route Shortening

• Node C notices that the source route to D can be
  shortened, since it overheard a packet from A
  intended first for B.

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Heterogeneous Networks

• An ad hoc network consisting of nodes with
  heterogeneous network interfaces

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DSR Heterogeneous Network
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AODV

• Ad hoc on-demand vector routing algorithm
• Unicast and Multicast support
• Builds routes only as desired by source nodes
• Forms trees to connect multicast members
• Route Request (RREQ) and Route Reply (RREP) for
  route setup
• Intermediate nodes record route
• Route times out after data transfer completes

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AODV Protocol Messaging

• Reference http//moment.cs.ucsb.edu/pub/wwan_chak
  eres_i.pdf

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Concluding Remarks

• Many issues in routing
• Active area of research. Lab3
• No standards yet
• Is a standard even possible?

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References

• Johnson et. al., DSR The Dynamic Source Routing
  Protocol for Multi-Hop Wireless Ad Hoc Networks.
• AODV, http//moment.cs.ucsb.edu/AODV/aodv.html
• Charles E. Perkins, Elizabeth M. Belding-Royer,
  and Samir Das. "Ad Hoc On-Demand Distance Vector
  (AODV) Routing." IETF RFC 3561.

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Label Switched Routing (LSR)

• Labels applied to outgoing packets
• Labels stripped from incoming packets
• Labels are local to the node
• Need a control plane
• Same technology is used in high-speed routers
• MPLS (Multi-Protocol Label Switching)
• ATM

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LSR Control Plane

• Resource Reservation Protocol (RSVP)
• RESV request
• PATH request
• Periodic refresh of LSP states
• Relies on raw IP
• Label Distribution Protocol (LDP)
• Label Request
• Label Mapping
• HELLO messages for existence of adjacent nodes
• Keep-alive messages to maintain TCP connection

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RSVP
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Label Switched Path

• Reference http//www.informit.com/articles/articl
  e.asp?p391649rl1

FEC Forwarding Equivalence Class