Self Configuring

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Self Configuring Self Organizing Protocols
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Outline

• Background.
• Taxonomy of Sensor Network Applications.
• Policy Decisions Assumptions for the
  self-configuring architecture.
• Terminology used.
• Architecture for the self-configurable systems.
• A Self-Organizing algorithm and its analysis.
• References.

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Background
4
Background

• Why do we need self-organizing protocol?
• Wireless Sensor Networks are used in
  applications where
• They are deployed in large numbers (hundreds or
  thousands of sensor nodes).
• They are deployed in remote/hostile environment.
• Systems in which sensor nodes need to
  self-organize themselves into a network belong to
  the class of self configurable systems.

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Terminology
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Terminology

• Sensor Motes
• Sensor node that performs data discovery
• Sink Node
• Node with high processing capabilities and high
  capacity for data storage
• Specialized Sensor
• Sensor that performs specific data discovery
  operation (e.g. temperature sensors)
• Router Sensor
• Router sensor collects and transmits data to
  neighbors

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Terminology

• High-End System
• Sink node
• 2-Connected Graph
• Topology in which there are two edge disjoint
  paths from every node to every other node
• Broadcast Graph
• Subset of edges in the network used for
  broadcasting data
• Directed Acyclic Graph (DAG)
• Graph with directed edges and no cycles

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Taxonomy of Sensor Network Applications
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Taxonomy of Sensor Network Applications

• Classifying sensor network applications
• Important Factors
• Size of the system number of sensors used
• Determine effort needed to configure the system
• Maximum distance of the sensors to the wired
  infrastructure
• Determines the amount of intelligence required at
  a sensor for routing to specific high processing
  nodes
• Distribution of the sensor nodes
• Deterministic administrator controls placement
  of sensor nodes and user performs remedial
  operations in case of faults
• Non-deterministic fault-tolerance level depends
  on number of sensors deployed

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Taxonomy of Sensor Network Applications

• Three classifications of sensor network
  applications
• Non-propagating systems
• Sensor nodes are one hop to wired infrastructure
• Wired infrastructure is the main connecting
  component
• Nodes connected to the wired infrastructure route
  information to the end system

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Taxonomy of Sensor Network Applications
Wired Nodes
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Taxonomy of Sensor Network Applications

• Deterministic routing systems
• Sensor nodes route through a few hops to reach a
  wired infrastructure
• Routes to the wired infrastructure are
  deterministic
• Number of nodes in this system may be restricted

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Taxonomy of Sensor Network Applications
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Taxonomy of Sensor Network Applications

• Self-configurable systems
• Sensor nodes need to self-organize into a network
• As long as the number of nodes in the system is
  small the systems are deterministic.
• But when the number of nodes increase the systems
  become non-deterministic systems and they need to
  be self-configurable.(e.g. Security and Parking
  Lot networks)
• Fault tolerance is achieved through
  re-configuring the system in the presence of new
  node and link failures

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Taxonomy of Sensor Network Applications
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Taxonomy of Sensor Network Applications

• Non-Aggregating
• Independent data
• Transmitted separately
• E.g. parking-lot systems
• Aggregating
• Data aggregating and transmitted along the
  network.
• E.g. weather applications
• Self-configuring sensor networks should include
  the functionality of performing aggregation too.

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Policy Decisions Assumptions for the
Architecture of Self-configuring systems
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Policy Decisions Assumptions

• Heterogeneous nodes
• Architecture should provide a common framework
• Data Discovery Data Dissemination
• Two orthogonal components
• Nodes that perform data discovery
• Nodes that perform data dissemination

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Policy Decisions Assumptions

• Memory and Power Constraints
• All nodes have memory and power constraints
• Attempt to reduce state stored at every node
• Employ energy aware routing
• Application Specific Infrastructure Requirements
• Infrastructure components is dependent on
  application
• Provide a wide variety of features to allow the
  application to make use of what is required

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Policy Decisions Assumptions

• Mobility/Immobility of nodes
• Data discovery nodes are mobile
• Data dissemination nodes are stationary
• Previous Works
• Multi-functional nodes
• Cost more to implement
• Routing in highly specialized nodes wasting
  energy
• Storage of mass information
• Data-Centric Networking
• Critical nodes need to keep large amounts of
  state information
• Cut nodes can cause the data to be lost

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Policy Decisions Assumptions

• Self-Configurable systems require one or more of
  the following
• Naming/Addressing System
• Routing
• Required to pass information to sensors with
  specific functionality
• Unique addresses to every node required
• Broadcasting
• Required to pass information to every sensor in a
  network (e.g. a wakeup message to all nodes in a
  security network)
• Multicasting

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Main Contribution of the Algorithm
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Main Contribution of the Algorithm

• Scalability
• Every node has a O(log n) bit unique identifier
• Reduction of State and Localized Operations
• Maintain O(log n) O(N(v)) state information
  at each node
• N - of nodes
• V current node
• N(v) - of neighboring nodes of v in network

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Main Contribution of the Algorithm

• Power Efficiency and Reliable Paths
• Keeps track of the power requirements at every
  node to compute reliable and power efficient
  paths
• Hierarchical Routing Architecture
• Nodes reorder themselves in a hierarchical
  structure
• Size of routing table is reduced to O(log n) at
  every node

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Main Contribution of the Algorithm

• Fault-Tolerant Broadcast Trees
• Local Markov Loops (LML) technique is used to
  achieve fault tolerance
• Reduce Frequency of Updates
• Define discrete power levels to reduce the number
  of dynamic cost updates that need to be performed
  in the network

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ComponentsInfrastructure
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Components

• Sensors
• Specialized
• Identifies itself with a class
• Can communicate with other sensors either of its
  own class or with some other class
• Can be Mobile
• Routing
• Form the backbone of the sensor network
• Immobile
• Performs data-dissemination

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Components

• Advantages
• Separation of dissemination and discovery
• Shorter network hops reduces power consumption
• Cost decreased routing sensors are not
  specialized and may cost less
• Large amounts of routers can increase the fault
  tolerance of the system

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Components

• Other components
• Sink Nodes
• High storage capacity high processing power
• Can connect to WAN
• Can activate specific actuators (through
  messaging) and broadcast important messages into
  the sensor net.
• Aggregator Nodes
• Nodes with the functionality of aggregation can
  be introduced in router nodes or specialized
  nodes
• E.g. In weather monitoring application
  aggregation functionality is placed on all router
  nodes

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Infrastructure Components

• Functionalities provided by this architecture
• Unique address for all nodes
• Routing information between two nodes
• Fault-Tolerant broadcasting infrastructure
• Broadcasting information within a certain radius
• Multicasting information to specialized nodes
• Self-reorganization in the face of node failures
  and network partitions

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Infrastructure Components

• Scenarios in which these components are used
• Security Sensors
• Unique Addresses to pass critical information to
  that sensor
• Routing Architecture to send messages to sink
  nodes
• Multicasting infrastructure to coordinate actions
  of specialized sensors of a particular class
• Broadcast infrastructure to alert all nodes
  within a radius to prepare to perform important
  actions

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Infrastructure Components

• Parking-Lot Networks
• Unique Addressing to isolate a particular node
  controlling a particular spot
• Routing Infrastructure for routing messages
• Broadcast Infrastructure not generally required
  but may be utilized

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Infrastructure

• Addressing Infrastructure
• If non-addressable nodes (e.g. traffic monitoring
  along a highway)
• Self-configurable systems is an aggregating
  system
• If addressing required - Local Unique Addressing
• IP not appropriate global unique addressing
• An alternative solution
• An alternative solution for addressing - MAC
  Layer
• Ensure that every node has a unique MAC address.

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Infrastructure

• Routing Infrastructure
• Specialized nodes must be adjacent to a router
• Transmits all messages to adjacent router with a
  message header
• Indicates which node(s) to transmit the message
  to (whether to one node or broadcast or
  multicast)
• Router acts as the proxy for the specialized
  node(s) i.e. every specialized node is addressed
  with the help of a router node.

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Infrastructure

• Broadcast and Multicasting Infrastructure
• Sensor networks are more data centric
• Require broadcasting and multicasting of data to
  all or groups of sensor nodes
• Fault Tolerant Broadcast tree is created
• Changes developing Local Markov Loops (LML)
• Directed Acyclic Graphs (DAG) are used to support
  fault tolerance in paths
• Participants
• Router sensors self-configure
• Specialized sensors keep track of the nearest
  router sensors

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Self-Organizing Algorithm
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Self-Organizing Algorithm

• Phases of the algorithm
• Discovery Phase
• Organization Phase
• Maintenance Phase
• Self-Reorganization Phase

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Discovery Phase

• Each node discovers its set of neighbors and
  fixes its maximum radius of data transmission
• Criteria
• Nodes should not have too many neighbors
• Specialized nodes n(x) 1
• Router nodes, n(x) gt 1
• where n(x) is the number of neighbors for node x
• Maximum bound on transmission radius
• Each node x picks a small radius r and broadcasts
  a Hello message indicating whether it is a router
  or a special node

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Discovery Phase

• Every node within radius r replies back with a I
  am Here message and their coordinates (determined
  by GPS)
• If of replies lt minimum threshold n(x), x
  broadcasts Hello over radius kr, for k gt 1
• Repeat until of nodes N that replies satisfies
• n(x) ? N ? N(x) where n(x) and N(x) denote the
  min and max number of neighbors to node x.
• Note that specialized nodes are only connected to
  routers only.

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Discovery Phase
Hello
r
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Discovery Phase
I am here
r
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Discovery Phase
Hello
kr
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Discovery Phase
I am here
kr
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Organization Phase

• Network is organized as follows
• Nodes are aggregated into groups
• Groups are aggregated into larger groups to form
  a hierarchy of groups which is height balanced
• Each node is allocated an address based on its
  position in the hierarchy
• A routing table of O(log n) is computed for each
  node
• A broadcast tree and graph spanning all nodes is
  constructed
• Graph is converted into a DAG based on the source
  node in the network

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Organization Phase

• Group formation
• Routers form small basic groups with neighbors
  found
• Group size is restricted to 8 and each node in a
  group is allocated a 3-bit address.
• Each node belongs to one basic group
• Each node maintains the distance and the next hop
  for reaching every other node in the group
• If a node is unable to join a group
• It forms a one node group with address 000
• ? is the height difference parameter.

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Organization Phase

• Merging of Groups
• Assume 2 groups G1 and G2 with m n bit
  address. For the formation of hierarchy set the
  value of ? to 3 equal to the height of a basic
  group.
• If m-n ? ? the G1 and G2 are merged to G with
• 0 appended to all node addresses in G1
• 1 appended to all node addresses in G1
• If m-n gt ? then
• Consider node x in G1 with address (x1, x2, xm)
• Consider subgroup Hi in G1 with 1st i bits equal
  to (x1, x2, xi) for i ? m-n-1.
• All nodes in Hi are connected.

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Organization Phase

• Find if Hm-n-1 has a sub-branch where G2 can be
  added to hierarchy without affecting Height of
  Hm-n-1 or G2.
• If not able to merge them at any value of i, then
  merge them according to the 1st method and mark
  the new graph as height imbalanced.
• A boundary node is a node that connects to a node
  in another group

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Organization Phase

• Formation of hierarchy
• Each Group G receives an advertisement from
  adjacent groups through its boundary nodes
• Broadcast throughout the group
• Contains size of adjacent group ( of address
  bits)
• Each node concludes on an adjacent group G
• G closest in size to G.
• G has the maximum number of boundary nodes.
• then node of G sends a join message to G.
• If G decides to join G, the groups merge
• Otherwise G selects the next best group H

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Organization Phase

• Continue until all groups merge into one
• At any point, If a group is heavily imbalanced,
  then the group is reorganized with an increased
  value of ?new ?old 1
• Theorem 1 Height of the hierarchy of the network
  will be O(log n) where n is the number of nodes
  in the graph

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Organization Phase

• Perform group reorganization if necessary
• If height is unbalanced at multiple levels,
  reorganize
• Group is broken into sub-groups
• Regroup without affecting the state of the rest
  of the network
• Some routing tales of nearby nodes will have to
  change addresses of neighbors
• Generate addresses for all nodes
• To give a general picture, if ? 3, then every
  node in a network of 10000 nodes will have a 16
  bit address.

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Organization Phase

• Routing table generation
• Let every node have a m-bit group address
• (x1,xm) is the m-bit address of a router node x
• x maintains the least cost and next hop in the
  shortest path to the following destinations
• x1, (x1, x2),,(x1,,xm-1,xm)
• E G., Let m 4, x address 0011
• Groups 1, 01, 000, and 0010 are maintained in the
  routing table for x
• routing table of O(m) at each node

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Organization Phase

• Broadcast Trees and Graphs
• Broadcast graphs are intended to provide multiple
  paths from the source
• adding fault tolerance to the system
• They are converted to DAG from the source
• to remove any loops
• To reduce power consumption
• Certain links are indicated as primary and rest
  as secondary
• Broadcast messages are sent through broadcast
  links
• Only secondary links follow a 3-way handshake
  mechanism

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Organization Phase

• Broadcast Tree and Graph formation
• After basic group formation, a broadcast tree and
  graph are constructed
• Some nodes are labeled as primary nodes. They
  form the broadcast tree
• After group merge (G H), two low cost edges
  (e1, e2) are selected that connect G and H
• Let B(G), B(H), T(G), T(H) be broadcast graphs
  and trees of G and H
• Let cost(e1) lt cost(e2)
• Let P be the merged group
• B(P) B(G) ? B(H) ? (e1, e2)
• T(P) T(G) ? T(H) ? (e1)

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Organization Phase

• Theorem 2 The power consumed for broadcasting
  messages using this approach is
• (n-1)E nE/2
  where
• E is the mean power consumed for sending a long
  message along one hop
• E is the mean power consumed for sending a
  request/ACK short message along one hop and
• n is the number of nodes in the network
• The SPIN protocol consumes (n-1)E 2eE..where
• e is the number of edges in the graph
• (n-1)E is the lower bound for broadcasting

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Organization Phase

• E.g., Sensors separated by 10 meters
• It takes 150nJ per bit transmitted
• 170nJ per bit received
• 1 request/ACK requiring 8 bytes
• E 20480nJ, in a network of 1000 nodes with
  average connectivity of 12
• Berkleys self-organizing algorithm requires an
  extra 10mJ
• SPIN requires an extra 240mJ
• Hence our algorithm saves by a factor of 24.

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Maintenance Phase

• Active monitoring
• Each node keeps track of its stored energy and
  constantly sends I Am Alive message to neighbors
  every 30 seconds
• If a node does not receive a reply in 6
  consecutive intervals it sets the link as dead
  and reorganizes
• Passive monitoring (energy saving)
• A node sends an activate message to its neighbors
  only on demand and Alive nodes respond with a ACK

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Maintenance Phase

• Routing Metrics
• Delay is not considered important in sensor
  networks
• Perhaps not true in cases of security and maybe
  even weather patterns
• Goal Keep network alive for a maximum amount of
  time

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Maintenance Phase

• Two Greedy metrics suggested
• Always route along the path that has the minimum
  energy consumption per bit of information
  transmitted
• Always transmit along the path that has the
  maximum capacity measured in terms of bits that
  can be transmitted
• Capacity of the link between nodes A and B is
  given by, min(E(A)/E,E(B)/E), where E(A) and
  E(B) are the energies at A and B respectively and
  E and E are the energy consumed by A and B
  transmitting from A to B.

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Maintenance Phase

• Maintaining Routing Tables
• Nodes inform their neighbors of their routing
  tables and their energy levels to their
  neighboring nodes (cost metric)
• Count to infinity problem can be avoided by using
  the next hop entry for updating the routing table
  entry for a particular destination group
• Maintaining Broadcast Infrastructure
• Must detect node failures in advance by
  monitoring power requirements of a node
• Only failures detected are those do to power
  failure

60
Maintenance Phase

• Fault tolerant broadcast trees and graphs are
  maintained using LML
• Node that is going to fail is a leaf node
• Therefore, does not have any nodes to broadcast
  to
• If node u is going to fail
• Consider all edges (u,v)
• Construct a LML by selecting a random edge (w,x)
  s.t. the edge (u,v) is part of a local loop
  formed by adding the edge (w,x) to the tree
• Remove (u,v) from the tree
• New tree with degree of u reduced by 1
• Continue until u becomes the leaf node

61
Reorganization Phase

• Detection of group partitions or node failures
• Update routing table based on new topology
• When all neighbors of a node fail
• Node repeats discovery phase
• When group partitions occur
• Sub groups reorganize and join
• Reorganization ensures hierarchy is balanced
• Group and node discoveries are considered very
  rare

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Reorganization Phase

• Re-organization
• Node Failures
• Every neighbor of the node updates all the
  entries in their routing table where the next hop
  is the failed node
• Link Failures
• The routing table is changed accordingly at both
  nodes
• If the edge is a primary edge, the secondary edge
  becomes primary and local loop is performed to
  find an alternate edge
• Group Partitions
• Disconnected pieces are reorganized into new
  groups and merge with other neighboring groups
• Address of all the nodes in the groups change

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Analysis of Algorithm

• Node Rediscovery
• Initial radius is set to the previous maximum
  radius of connectivity
• Strengths
• Hierarchy formed by algorithm is strictly
  balanced
• Max difference between the left subtree and right
  subtree at any level is strictly les than or
  equal to ?
• Routing state maintained at any router is O(log
  n)
• Broadcast graph (2-connected) is incrementally
  computed

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Analysis of Algorithm

• LML performs a random walk on spanning trees of a
  graph providing tolerance to node and link
  failures
• Broadcast graph can be oriented as a Directed
  Acyclic Graph from any node in a unique manner.
• The property that every specialized sensor
  attaches to some router sensor allows these
  sensors to be mobile

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Analysis of Algorithm

• Weaknesses
• Initial Organization phase and not on-demand
  organization
• Forming a hierarchy in cases where there are a
  lot of cut nodes in the network increases the
  probability of applying reorganization
• Protocol required for transmitting data from one
  node to another node is not addressed
• Broadcast trees and graphs maintenance in the
  presence of failures undetected prior to failure
  is not addressed

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References
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References

• S Subramanian, L. and Katz, R., An
  Architecture for Building Self-Configurable
  Systems, Dept. of EECS, U. C. Berkeley, 2000,
  pp. 63-73.
• C. Chevallay, R. E. Van Dyck, T. A. Hall,
  Self-Organizing Protocols for Wireless Sensor
  Networks, NIST Gaithersburg, MD, 2002.