Wireless Routing Protocol Mobile Ad hoc NETwork MANET

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Wireless Routing Protocol--- Mobile Ad hoc
NETwork (MANET)

• Prof. Gao
• ECE697A Fall 2003
• Advanced Computer Networks

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Outline

• MANET overview
• Connectivity Routing in MANET
• Routing with special constraints
• Open issues and future directions

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Point-to-multipoint networks

• Cellular networks
• IEEE 802.11

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Mobile Ad Hoc Networks

• Formed by wireless autonomous hosts
• Without (necessarily) using a pre-existing
  infrastructure
• Routes between hosts may potentially contain
  multiple hops
• Host mobility cause route changes
• Shared wireless channel

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Why Ad Hoc Networks ?

• Ease of deployment
• Speed of deployment
• Decreased dependence on infrastructure
• User flexibility

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Application areas

• Military environments
• Battle field sensors, soldiers, vehicles
• Emergency operations
• search-and-rescue
• policing and fire fighting
• Civilian environments
• conference halls
• sports stadiums, Library, etc.
• Personal area networking
• laptop, PDA, cell phone, ear phone, wrist watch

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Challenges

• Lack of centralized entity
• Shared unreliable wireless medium
• Low bandwidth
• Hidden/exposure node effect
• Ease of snooping on wireless transmissions
• Mobility-induced route changes/packet losses
• Battery constraints
• Asymmetric Capabilities
• transmission ranges
• battery life
• processing capacity
• Speed/pattern of movement

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Why is Routing in MANET Different?

• Host mobility
• link failure/repair due to mobility
• different characteristics than those due to other
  causes
• Rate of link failure/repair may be high when
  nodes move fast
• Distributed Environment
• New performance criteria may be used
• Route stability despite mobility
• Packet delivery ratio
• Routing Overhead

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Ad hoc Routing Protocols

• Proactive protocols (DSDV)
• Reactive protocols (AODV, DSR)
• Hybrid protocols (OLSR, ZRP, CEDAR)
• Which approach achieves a better trade-off
  depends on the traffic and mobility patterns

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Proactive Protocols

• Destination-Sequenced Distance-Vector (DSDV)
• Features
• Traditional distributed shortest path routing
  protocols
• link-state or distance-vector protocol
• Continuously update the reachability
  information at all the network nodes
• Lower route request latency and higher overhead

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Reactive Protocols

• Ad hoc On Demand Distance Vector Protocol (AODV)
• Dynamic Source Routing Protocol (DSR)
• Features
• Maintain routes only if needed
• Flooding of control message
• higher latency and lower overhead
• Source routing/hop-by-hop routing

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Hybrid Protocols

• Optimized Link State Routing Protocol (OLSR)
• Zone Routing Protocol (ZRP)
• Core-Extraction Distributed Ad hoc Routing
  (CEDAR)
• Features
• Constrained link state maintenance
• Route established on-demand

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DSDV

• Destination Sequenced Distance Vector routing
  protocol
• Proactive
• Each node maintains its own sequences number
• Updates (increments) at each change in
  neighborhood information
• Used for loop freedom
• Each node maintains routing table with entry for
  each node in the network

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DSDV --- Routing Table at MN4

• Dest Nexthop Metric DestSequence
  InstallTime
• MN1 MN2 2 406
• MN2 MN2 1 128
• MN3 MN2 2 564
• MN4 MN4 0 710
• MN5 MN6 2 392
• MN6 MN6 1 076
• MN7 MN6 2 128
• MN8 MN6 3 050

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DSDV routing updates

• Each node periodically transmits updates
• Includes its own sequences number, routing table
  updates
• Nodes also send routing table updates for
  important link changes
• When two routes to a destination received from
  two different neighbors
• Choose the one with greatest destination sequence
  number
• If equal, choose the smaller metric (hop count)

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DSDV --- full dump

• Full Dumps
• Carry all routing table information
• Transmitted relatively infrequently
• Incremental updates
• Carry only information changed since last full
  dump
• Fits within one network protocol data unit
• If cant, send full dump

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DSDV --- link additions

• When A joins network
• Node A transmits routing table ltA, 101, 0gt
• Node B receives transmission, inserts ltA, 101, A,
  1gt
• Node B propagates new route to neighbors ltA, 101,
  1gt
• Neighbors update their routing tables ltA, 101,
  B, 2gt and continue propagation of information

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DSDV --- link breaks

• Link between B and D breaks
• Node B notices break
• Update hop count for D and E to be infinity
• Increments sequence number for D and E
• Node B sends updates with new route information
• ltD, 203, infinitegt
• ltE, 156, infinitegt

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DSDV --- Summary

• Routes maintained through periodic and event
  triggered routing table exchanges
• Incremental dumps and settling time used to
  reduce control overhead
• Lower route request latency, but higher overhead
• Perform best in network with low to moderate
  mobility, few nodes and many data sessions
• Problems
• Not efficient for large ad-hoc networks
• Nodes need to maintain a complete list of routes.

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AODV

• The Ad-hoc On-Demand Distance Vector Algorithm
• Reactive
• Route discovery cycle used for route finding
• Maintenance of active routing
• Sequence number used for loop prevention and
  route freshness criteria
• Descendant of DSDV
• Provides unicast and multicast communication

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AODV --- Goal

• Quick adaptation under dynamic link conditions
• Lower transmission latency
• Consume less network bandwidth (less broadcast)
• Loop-free property
• Scalable to large network

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AODV --- unicast route discovery

• RREQ (route request) is broadcast
• Sequence Number
• Source SN freshness on reverse route to source
• Destination SN freshness on route to destination
• RREQ message
• ltbcast_id, dest_ip, dest_seqno, src_seqno,
  hop_countgt
• RREP (route reply) is unicast back
• From destination if necessary
• From intermediate node if that node has a recent
  route

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AODV --- multicast route discovery

• Message types
• RREQ, with new flags
• Join and Repair
• RREP
• MACT (Multicast activation message)
• Multicast routes have destination sequence number
  and multiple next hops
• Multicast group leader extension for RREQ and RREP

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AODV --- route discovery (1)

• Node S needs a route to D
• Create a route request (RREQ)
• Enters Ds IP address, sequence number, Ss IP
  address, sequence number
• Broadcasts RREQ to neighbors

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AODV --- route discovery (2)

• Node A receives RREQ
• Makes reverse route entry for S
• Dest S, nexthop S, hopcount 1
• It has no route to D, so it broadcasts RREQ
• Node C receives RREQ
• Makes reverse route entry for S
• Dest S, nexthop A, hopcount 2
• It has route to D seq for route D gt seq in
  RREQ
• Creates a route reply (RREP)
• Enters Ds IP address, sequence number, Ss IP
  address, hopcount
• Unicasts RREP to A

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AODV --- route discovery (3)

• Node A receives RREP
• Unicasts RREP to S
• Makes forward route entry to D
• Dest D, nexthop C hopcount 2
• Node S receives RREP
• Makes forward route entry to D
• Dest D, nexthop A hopcount 3
• Sends data packets on route to D

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AODV --- route maintenance (1)

• Link between C and D breaks
• Node C invalidates route to D in routing table
• Node C creates route error (RERR) message
• Lists all destinations with are now unreachable
• Sends to upstream neighbors
• Node A receives RERR
• Checks whether C is its next hop on route to D
• Deletes route to D, and forwards RERR to S

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AODV --- route maintenance (2)

• Node S receives RERR
• Checks whether A is its next hop on route to D
• Deletes route to D
• Rediscovers route if still needed

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AODV --- Optimizations

• Expanding ring search
• Prevents flooding of network during route
  discovery
• Control Time to Live of RREQ
• Local repair
• Repair breaks in active routes locally instead of
  notifying source
• Use small TTL because destination probably has
  not moved far
• If first repair attempt is unsuccessful, send
  RERR to source

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AODV --- Summary

• Reactive / On-demand
• Sequence numbers used for route freshness and
  loop prevention
• Route discovery cycle
• Maintains only active routes
• Optimization can be used to reduce overhead and
  increase scalability

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Hybrid Protocols

• Proactive protocol
• Pro-actively updates network state and maintains
  route regardless of whether any data traffic
  exists or not
• Reactive protocol
• Only determines route to a destination if there
  is some data to be sent to the destination

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Hierarchical ad hoc network
A two-tier Ad hoc Network
Tier 2 network
Cluster
cluster head
Tier 1 network
Tier 1 network
Tier 1 network
Tier 1 network
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CEDAR

• Core-Extraction Distributed Ad Hoc Routing
• Dominator Set
• Each node is in dominator sets or is the neighbor
  of one dominator node
• Minimum Dominator Set and the links which length
  is no greater than 3 construct the core

Minimum Dominator Set and Core
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Core Extraction

• Core extraction
• Establishment maintenance of a routing
  infrastructure called core
• Finding core (Minimum Connected Dominating Sets)
  is NP-complete
• Each node picks one core node as its dominator
• Dominator node is chosen based on degree of the
  outgoing link
• Periodical Link state propagation
• propagation of the link-state of stable
  high-bandwidth links in the core

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Route Computation

• Route computation
• route computation at the core nodes using all
  pair shortest path algorithm

S
D
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CEDAR --- Route Discovery

• Node S informs its dominator core node A
• Node A finds a route in the core network to the
  core node B which is the dominator for
  destination D
• Core nodes on the above route between A and B
  then build a route from S to D using locally
  available link state information

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CEDAR --- Summary

• Advantages
• Route discovery/maintenance duties limited to a
  small number of core nodes
• Link state propagation is a function of link
  stability/quality
• Disadvantages
• Core nodes have to handle additional traffic,
  associated with route discovery and maintenance
• Hard to converge under high mobility

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Special Constraints

• Routing with special constrains
• Power
• Security
• QoS
• Open issues and future directions

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Power-Aware Routing criteria

• Define optimization criteria as a function of
  energy consumption. Examples
• Minimize energy consumed per packet
• Minimize time to network partition due to energy
  depletion
• Maximize duration before a node fails due to
  energy depletion

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Power-Aware Routing approach

• Assign a weight to each link
• Weight of a link may be a function of
• energy consumed when transmitting a packet on
  that link
• residual energy level
• Prefer a route with the smallest aggregate weight

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Security Issues in Mobile Ad Hoc Networks Whats
New ?

• Ad hoc network based on peer cooperation
• Can you trust your peer?
• Wireless medium is easy to snoop on
• Trace the path of active routes
• Easier for intruders to insert themselves into
  the network
• Everybody is a router
• inject erroneous routing information
• divert network traffic, or
• make routing inefficient

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Open Problems

• Address assignment problem
• Stationary or auto-configuration?
• Improving interaction between protocol layers
• Some routing protocol need feed back from MAC to
  detect link status
• Position information from higher layer
• Integration with Internet
• Existing ad hoc routing with infrastructure nodes
• Different network perspectives