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Mobile Ad hoc NETwork (MANET)
Outline
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MANET overview
Applications of MANET
Issues in MANET
MAC Protocols for MANET
Routing Protocols for MANET
Open issues and future directions
Infrastructure networks
(single hop)
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Cellular networks
IEEE 802.11
Mobile Ad Hoc Networks
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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
Mobile Ad Hoc Networks
MH2
MH4
MH
3
Asymmetric link
MH5
MH7
Symmetric link
MH
1
MH6
Why Ad Hoc Networks ?
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Ease of deployment
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Speed of deployment
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Decreased dependence on infrastructure
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User flexibility
Application areas
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Military environments
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Emergency operations
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search-and-rescue
policing and fire fighting
Civilian environments
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Battle field: sensors, soldiers, vehicles
conference halls
sports stadiums, Library, etc.
Personal area networking
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laptop, PDA, cell phone, ear phone, wrist watch
Challenges & Issues
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Medium Access Control
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Distributed Operation
Synchronization
Hidden & Exposed terminal problem
Access delay and Fairness
Real Time Traffic support
Low bandwidth
Ease of snooping on wireless transmissions
Routing
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Mobility-induced route changes/packet losses
High BER
Location-dependent contention
Looping
Distributed Routing
Challenges & Issues
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Transport Layer Protocols
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Energy Management
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UDP – Highly Unreliable, may result into increasing congestion
TCP – Frequent path breaks, stale routing information, high error
rate, frequent network partitions.
Battery energy management
Transmission Power management
Processor and device power management
Security
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Denial of Service attack (DoS)
Resource Consumption
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Energy Depletion
Buffer Overflow
Compromised Nodes
Interference
Challenges & Issues
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Deployment Constraints
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Environment
Area of Coverage
Asymmetric Capabilities
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transmission ranges
battery life
processing capacity
Speed/pattern of movement
MAC Protocols
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Goals
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Operation should be distributed
Support QoS for Real Time data
Minimize Access Delay
Fairness
Scalable
Power Control Mechnism
Adaptive Rate Control
Synchronization
MAC Protocols
Classification of MAC Protocols
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Contention-Based
Contention-Based with Reservation
Contention-Based with Scheduling
Why is Routing in MANET Different?
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Host mobility
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link failure/repair due to mobility
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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
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Route stability despite mobility
Packet delivery ratio
Routing Overhead
Routing Protocols in MANET
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Goals
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Fully Distributed
Adaptive to frequent topology changes
Route computation and maintenance must involve
minimum number of nodes
Routing state must be localized
Must be loop free and free from stale route
Converge must be quick
Efficient resource utilization like BW, comp power,
battery, memory
Provide QoS
Ad hoc Routing Protocols
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Proactive protocols (Table Driven) (Eg.DSDV)
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Reactive protocols (On-Demand)(Eg. AODV,
DSR)
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Hybrid protocols (ZRP, CEDAR)
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Which approach achieves a better trade-off
depends on the traffic and mobility patterns
Proactive Protocols
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Each node maintains a table having consistent, upto-date routing information from each node to
every other node.
Respond to changes by propagating updates to
throughout the network
Variations are on basis of number of tables
required and the way updates are propagated.
Features:
Traditional distributed shortest path routing protocols
link-state or distance-vector protocol
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Examples
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Destination-Sequenced Distance-Vector (DSDV)
Clusterhead Gateway Switch Routing (CGSR)
The Wireless Routing Protocol (WRP)
Reactive Protocols
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Creates route only when desired by the source node
Source initiates a route discovery process within the
network
Once a route has been established, it is maintained
by some form of route maintenance procedure
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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Examples
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Ad hoc On Demand Distance Vector Protocol (AODV)
Dynamic Source Routing Protocol (DSR)
Temporally-Ordered Routing Algorithm (TORA)
Associativity-Based Routing (ABR)
Hybrid Protocols
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Hybrid routing protocols are proposed to combine the merits of
both proactive and reactive routing protocols and overcome
their shortcomings.
Features:
 Constrained link state maintenance
 Route established on-demand
Examples
 Zone Routing Protocol (ZRP)
 Core-Extraction Distributed Adhoc Routing (CEDAR)
DSDV
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Destination Sequenced Distance Vector
routing protocol
Proactive
Each node maintains its own sequences
number
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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
DSDV --- Routing Table at MN4
Dest
MN1
MN2
MN3
MN4
MN5
MN6
MN7
MN8
Nexthop
MN2
MN2
MN2
MN4
MN6
MN6
MN6
MN6
Metric
2
1
2
0
2
1
2
3
DestSequence
406
128
564
710
392
076
128
050
DSDV routing updates
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Each node periodically transmits updates
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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
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Choose the one with greatest destination
sequence number
If equal, choose the smaller metric (hop count)
DSDV --- full dump
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Full Dumps
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Carry all routing table information
Transmitted relatively infrequently
Incremental updates
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Carry only information changed since last
full dump
Fits within one network protocol data unit
If can’t, send full dump
DSDV --- link additions
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When A joins network
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Node A transmits routing table: <A, 101, 0>
Node B receives transmission, inserts <A, 101, A, 1>
Node B propagates new route to neighbors <A, 101, 1>
Neighbors update their routing tables: <A, 101, B, 2>
and continue propagation of information
DSDV --- link breaks
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Link between B and D breaks
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Node B notices break
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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
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<D, 203, infinite>
<E, 156, infinite>
DSDV --- Summary
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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:
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Not efficient for large ad-hoc networks
Nodes need to maintain a complete list of routes.
Clusterhead Gateway Switch
Routing (CGSR)
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Similar to DSDV except addressing being
employed and network organization
Node are grouped into clusters. Clusterhead
selection algo (Least Cluster Change) is
employed to elect a clusterhead
Gateways are used to relay packets between
clusterheads.
Each node maintains cluster member table
which stores destination cluster head for each
node.
Also they maintain routing table, like DSDV to
CGSR---Routing
Routing from Node 1 to Node 8
CGSR--- Summary
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Easy to implement scheduling
Better utilization of resources
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Problems:
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Increase in path length
Instability at high mobility
The Wireless Routing Protocol
(WRP)
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Each node maintains 4 tables:
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Distance table
Routing table
Link-cost table
Message retransmission list (MRL)
DT contains matrix where each element contains
distance and penultimate node reported by neighbor
of a particular destination
MRL contains sequence no of update message,
retransmission counter, ack required flag for each
neighbor, list of update sent in update message
AODV
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The Ad-hoc On-Demand Distance Vector Algorithm
Reactive
Pure on-demand route acquisition system
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
AODV --- Goal
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Quick adaptation under dynamic link
conditions
Lower transmission latency
Consume less network bandwidth (less
broadcast)
Loop-free property
Scalable to large network
AODV --- unicast route discovery
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RREQ (route request) is broadcast
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Sequence Number:
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RREQ message
<bcast_id, dest_ip, dest_seqno, src_seqno, hop_count>
While forwarding, intermediate nodes record address of
neighbor from where first copy of RREQ is received, thus
creating reverse path.
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Source SN: freshness on reverse route to source
Destination SN: freshness on route to destination
AODV --- unicast route discovery
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RREP (route reply) is unicast back
From destination if necessary
 From intermediate node if that node has a recent
route
Intermediate node forwarding RREP stores this info
in their routing cache to set up a path to destination
Route timer is maintained with each entry. If idle for
some time delete that route
As RREP is always forwarded over path of RREQ, it
always expects symmetric links.
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AODV --- route discovery (1)
1. Node S needs a route to D
2. Create a route request (RREQ)
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Enters D’s IP address, sequence number, S’s IP
address, sequence number
Broadcasts RREQ to neighbors
AODV --- route discovery (2)
3. Node A receives RREQ
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Makes reverse route entry for S
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Dest = S, nexthop = S, hopcount = 1
It has no route to D, so it broadcasts RREQ
4. Node C receives RREQ
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Makes reverse route entry for S
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Dest = S, nexthop = A, hopcount = 2
It has route to D && seq# for route D > seq# in RREQ
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Creates a route reply (RREP)
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Enters D’s IP address, sequence number, S’s IP address, hopcount
Unicasts RREP to A
AODV --- route discovery (3)
5. Node A receives RREP
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Unicasts RREP to S
Makes forward route entry to D
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Dest = D, nexthop = C hopcount = 2
6. Node S receives RREP
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Makes forward route entry to D
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Dest = D, nexthop = A hopcount = 3
Sends data packets on route to D
AODV --- route maintenance (1)
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Link between C and D breaks
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Node C invalidates route to D in routing table
Node C creates route error (RERR) message
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Lists all destinations which are now unreachable
Sends to upstream neighbors
Node A receives RERR
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Checks whether C is its next hop on route to D
Deletes route to D, and forwards RERR to S
AODV --- route maintenance (2)
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Node S receives RERR
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Checks whether A is its next hop on route to D
Deletes route to D
Rediscovers route if still needed
AODV --- Optimizations
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Expanding ring search
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Prevents flooding of network during route
discovery
Control Time to Live of RREQ
Local repair
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Repair breaks in active routes locally instead of
notifying source
If first repair attempt is unsuccessful, send RERR
to source
AODV --- Summary
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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
Dynamic Source Routing
(DSR)
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Two Phases
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Route discovery
Route maintenance
Before transmitting, a node consults its route
cache. If unexpired route available, use that
route else begin route discovery by
broadcasting route request pkt.
RREQ contains add of Dest, Source Add,
unique ID
Dynamic Source Routing
(DSR)
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Node receiving the pkt checks, if it knows the route
to destination. If it does not then adds its own
address to record route and forward the pkt to next
neighbor.
RREP is generated by destination or any intermediate
node knowing path to destination.
Responding node can use path to initiator for RREP if
available else if symmetric links are supported,
reverse path in record route.
If symmetric links are not supported, initiate RREQ
with RREP being piggybacked
DSR
Dynamic Source Routing
(DSR)
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Route Maintenance – Whenever a link breakage is
noticed, route error pkt is generated and broadcated
and route containing that hop is deleted.
Apart from error pkt, ack is used to check correct
operation of links (typically passive ack)
Associativity Based Routing
(ABR)
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Route selection based stability of a route
Stability is measured based count of beacons
If a beacon is not received for some interval, count is
set to zero for a link
A link is stable is it is leading to a stable neighbor and
same way unstable link
Associativity Based Routing
(ABR)
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RREQ is flooded
Intermediate nodes forwards RREQ by appending its
address and beacon count in it.
When it reaches destination, dest waits for
TRouteSelectTime to receive more RREQ from different
paths
Select route with maximum proportion of stable links
If two routes with same proportion of stable links,
then choose shorter one.
But more priority is given to stability than length
Associativity Based Routing
(ABR)
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Route Maintenance
If a link is down, neighbor node detects the breakage
of link and initiates local recovery by broadcasting
route repair pkt called Local Query(LQ) broadcast
with limited TTL (Ex 2)
Advantages & Disadvantages
Routes are stable so less chance of link failure
Cons: Path may be longer
Repetition of LQ
Hybrid Protocols
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Proactive protocol:
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Pro-actively updates network state and
maintains route regardless of whether any
data traffic exists or not
Reactive protocol:
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Only determines route to a destination if
there is some data to be sent to the
destination
Zone Routing Protocol(ZRP)
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Uses best features of reactive and proactive
Uses proactive routing within a zone and reactive
outside the zone
Intra Zone Routing Protocol (IARP) and Inter Zone
Routing Protocol (IERP)
A routing zone of a given node is subset of nw within
which all nodes are reachable within less than or
equal to zone radius hops
Interior nodes and peripheral nodes
Each nodes maintains info abt all nodes in the zone
by periodic route update pkt (IARP)
Zone Routing Protocol(ZRP)
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When a pkt from s is to be transmitted to d
S checks whether d is in its routing zone, if yes it
uses proactive routing table
If no it broadcasts RREQ to all peripheral nodes
If they know they respond with RREP else they also
forward to their peripherals until the destination is
reached
All forwarding (RREQ) nodes appends their address
to the RREQ to deliver RREP on that path
Broken link is handled by local repair and a path
update message is sent to source
CEDAR
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Core-Extraction Distributed Ad Hoc Routing
Dominator Set
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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
Core Extraction
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Core extraction
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Establishment & maintenance of a routing infrastructure called
“core”
Finding core (Minimum Connected Dominating Sets) is NPcomplete
Each node picks one core node as its dominator
Dominator node is chosen based on degree of the outgoing
link
Periodical Link state propagation
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propagation of the link-state of stable high-bandwidth links in
the core
Route Computation
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Route computation
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route computation at the core nodes using all pair shortest path
algorithm
S
D
CEDAR --- Route Discovery
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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
CEDAR --- Summary
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Advantages
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Route discovery/maintenance duties limited to a
small number of core nodes
Link state propagation is a function of link
stability/quality
Disadvantages
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Core nodes have to handle additional traffic,
associated with route discovery and maintenance
Hard to converge under high mobility
Special Constraints
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Routing with special constrains
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Power
Security
QoS
Open issues and future directions
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
Power-Aware Routing: approach
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Assign a weight to each link
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Weight of a link may be a function of
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energy consumed when transmitting a packet on
that link
residual energy level
Prefer a route with the smallest aggregate
weight
Security Issues in Mobile Ad Hoc
Networks: What’s New ?
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Ad hoc network based on peer cooperation
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Wireless medium is easy to snoop on
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Can you trust your peer?
Trace the path of active routes
Easier for intruders to insert themselves into the
network
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Everybody is a “router”
inject erroneous routing information
divert network traffic, or
make routing inefficient
Open Problems
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Address assignment problem
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Improving interaction between protocol layers
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Stationary or auto-configuration?
Some routing protocol need feed back from MAC
to detect link status
Position information from higher layer
Integration with Internet
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Existing ad hoc routing with infrastructure nodes
Different network perspectives
Open Problems
Scalability
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Short-range Throughput per node decreases at a rate 1/
, where N is the
number of nodes
 This cannot be fixed except by physical layer improvements, such as
directional antennas
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Quality of service
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Need to provide best-effort service only for Voice, live video and file transfer
Client server model shift
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There is no server, but demand for basic services still exists.
 Address allocation, name resolution, authentication and service location are
just examples of very basic services which are needed
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Security
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Lack of any centralized network management or certification authority
Networks are particularly prone to malicious behavior
Interoperation with the Internet
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Networks require some Internet connection
Interface between the two are very different
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Energy conservation
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Lifetime of a single battery and the whole network.
Node cooperation
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Why anyone should relay other people’s data
Interoperation
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What happens when two autonomous ad hoc networks move into same area