MANETS

1
MANETS An overview
2
MANETs

• Model and Definitions
• Simulatability mobility models
• Routing algorithms
• Security issues with routing algorithms
• Tracing malicious faults
• Multipath Multichannel routing

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Model and Definitions

• Definition 1 Model of an ad hoc network
• Let V be a finite state system with state
  space S.
• The elements of V are mobile nodes
• -- each node is a probabilistic finite
  state machine
• A mobile ad hoc network is a random process
• G (G1,S1), (G2,S2), (GT,ST)
  
• where the G1 (V,Nt) are graphs with node
  set V and St ? S,
• subject to the following constraints

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Model and Definitions

• Markov constraint
• given (Gt,St) the next state (Gt1,St1) is
  independent of all previous states (G1,S!)
  (Gt-1,St-1)
• Mobility constraint
• The transitional probabilities Pr (Gt1,St1)
  (Gt,St) are independent of time t.
• The distribution ? generated by these is
  called the mobility distribution.

5
Model and Definitions

• Medium constraint
• The communication medium is
• is promiscuous
• has limited bandwidth
• is bidirectional

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Model and Definitions

• Definition 2 Simulatability
• G is simulatable if there is an efficient
  algorithm ? that simulates G , that is
  generates samples
• (G1,S1), , (Gt,St)
• such that
• Pr(G1,S1), , (Gt,St)
  Pr(G1,S1), , (Gt,St)

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Model and Definitions

• Definition 3 Route
• A route R(s,d) with source s and
  destination d is a
• list of nodes of G that start at s and end
  at d through which packets are forwarded.
• The nodes need not know the list, not even
  their successor on the list!

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Model and Definitions

• Definition 3 Adversary
• Let ? be a family of subsets V of V.
• We call ? an Adversary Structure.
• The adversary Adv Adv? selects a subset V
  of V
• and can corrupt all its nodes during the
  lifetime
• of the system.
• These nodes are called corrupted or faulty.
  
• Adv is called a ?- adversary.
• .

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Model and Definitions

• Definition 3 Adversary -- continued
• The adversary Adv may be passive or active.
• A passive adversary eavesdrops on the
  network
• communication.
• An active adversary uses the corrupted nodes
  to
• prevent the normal functioning of the
  network.

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Model and Definitions

• Definition 3 Adversary -- continued
• The Byzantine threats model
• For this model
• ? V ? V V k
• for some threshold k.
• In this case the adversary can corrupt up to
  k nodes.

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Mobility models

• The Random Walk model
• Nodes move in turns
• Each node at the beginning of its turn selects at
  random
• a value v for its velocity
• a value ? for its direction, and
• a value t for the duration of the turn.
• Alternatively instead of t a value d for the
  distance to be traveled is selected.
• Problem Brownian motion

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Mobility models

• The Random Waypoint model
• An extension of the Random Walk model.
• Each node at the beginning of its turn first
  moves to
• a new position selected at random in the unit
  square.
• Problem This addresses the Brownian motion, but
  now
• Nodes congregate to the centre of the unit
  square.
• Solution Wrap around the parallel edges of the
  square
• to get a torus now nodes can cross over
  boundaries.

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Mobility models

• The Random Waypoint model
• Problem There is an speed decay for the nodes.
• Solution Use special distribution of nodes at
  start time,
• minimum speed and warm up period.
• Problem Abrupt changes in node direction at the
  
• beginning of turns.

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Mobility models

• The Random Direction model
• An extension of the Random Waypoint model.
• Each node at the beginning of its turn first
• chooses
• -- see the Notes for a more control between the
  deterministic and random movement of nodes

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Mobility models

• Group models
• Group behavior is simulated by using a common
• reference point.
• As the reference point moves, the nodes move
  along
• with it.

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Mobility models

• Nomadic group model
• Nodes move randomly around the common reference
• point.

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Mobility models

• Target group model
• The common reference point is used as a target.

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Mobility models

• Hybrid models
• The movement of the common reference point is
• simulated by using one of the first three non
  group
• models.
• All these models are Markovian

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Mobility models

• Ad Hoc Network simulators
• Discussion on (and toy implementation?) of
• ns2
• OPNETR modeler
• GLoMoSim

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Routing algorithms

• Definition
• Routing ( Pathfinder, Communication )
• Pathfinder is a distributive algorithm that
  takes as input G, s,d and generates a path ? that
  links s,d. Path information ?xi
• is then distributed to all nodes on the path
• With source-centric routing, the source gets the
  complete path (from neighbor lists).
• With network-centric routing the path
  information is distributed among the nodes of ?
  (as distance vectors).
• -----------------------------------
• See later for definitions

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Routing algorithms

• Communication is a distributed algorithm on ?.
• On input data to s
• s broadcasts pkts (headers,data),
• If xi ? s,d on ? receives pktxj, it verifies
  it, and if correct computes and broadcasts
  pktxj (headerxj,data).
• If d receives pktxk, it verifies it, and if
  correct outputs data.
• headerx contains information about the path ?
  known to x.
• From this information, and from the local path
  information
• distributed by Pathfinder, any neighbor y of x
  can
• determine whether it is on ?, and if so, it
  computes headery
• and broadcasts pkty.
• Eventually, if s,d are linked in G, data will be
  delivered to the
• destination d.

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Routing algorithms

• Definition
• Routing is reliable if
• when Adv is passive, on input G, s,d
  any data input to s will be
  delivered to d.
• Routing will tolerate ? , if it is reliable in
  the presence of any active ? - adversary.

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Routing algorithms

• Definition
• Routing updates
• Route settling

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Routing algorithms

• Definition
• There are two types of routing
• network-centric and
• source-centric.
• With network-centric routing the routing effort
  is
• distributed within the network discussion on
  tables and
• vectors. With source-centric routing most of the
  effort is
• done by the source, with the other nodes
  restricted to
• relaying packets and usually making only minor
  checks.

25
Routing algorithms

• Discussion on basic source-centric routing
  algorithms
• DSDV, AODV, WRP, etc (Tina Suen)
• Discussion on basic network-centric routing
  algorithms
• DSR etc

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Security issues for routing algorithms

• From a security point of view network-centric
  routing requires substantial cooperation between
  nodes and strong trust relations. These
  algorithms are therefore more vulnerable to
  malicious faults
• Source centric routing lessens the dependency on
  node cooperation and therefore is less vulnerable
  to malicious attacks.

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Security associations and PKIs

• Crypto mechanisms are used to support the basic
  security requirements for ad hoc networks.
• Whether secret key or public key systems are used
  security associations must be established between
  the nodes of the network.
• One way is to use an external PKI
• Other ways to be discussed in class.