Wireless networks - Lecture 28: Mobile Ad-hoc network
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Wireless Networks
Lecture 28
Mobile Ad hoc Network
Dr. Ghalib A. Shah
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Outlines
Introduction
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What is Ad hoc networks?
Characteristic
Ad hoc vs. cellular networks
Application
Challenges
Routing Protocol
► Expected Properties of Ad-hoc Routing Protocols
► A taxonomy for routing protocols in Mobile ad
► Some common protocols (DSDV, AODV, DSR, ZRP,
TORA)
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Last Lecture Review
Problems with DCF
Virtual Carrier Sensing
RTC/CTS Protocol
Interframe Spacing
PCF
Fragmentation / Reassembly
MAC Frame Format
Frame Types
Physical Media in Original IEEE 802.11
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What is Ad hoc
Ad hoc
► For a specific purpose of occasion
► For this case alone
IEEE802.11
► a network composed solely of stations within mutual
communication range of each other via the wireless
media.
► an independent basic service set
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Mobile distributed multi-hop wireless network
(manet)
► a group of mobile, wireless nodes which
cooperatively and spontaneously form a network
independent of any fixed infrastructure or centralized
administration
► A node communicates
• directly with nodes within wireless range
• indirectly with all other destinations using a dynamically
determined multi-hop route though other nodes in the
manet
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The characteristic of ad hoc networks
Heterogeneous nodes
Self-creating
► not rely on a pre-existing fixed infrastructure
Self-organizing
► no predetermined topology
Self-administering
► no central control
creating a network “on the fly”
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Ad hoc networks
► infrastructureless
► multiple hop
• Radio power limitation, channel utilization, and powersaving concerns
► DCF(distributed coordination function)
Cellular networks
► infrastructure-based
► one hop(uplink or downlink)
► PCF(pointed coordination function)
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Challenges
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Spectrum allocation
Self-configuration
Medium access control (MAC)
Energy efficiency
TCP Performance
Mobility management
Security & privacy
Routing protocols
Multicasting
QoS
Service Location, Provision, Access
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Routing Protocols
Expected Properties of Ad-hoc Routing
Protocols
A taxonomy for routing protocols in Mobile ad
hoc networks
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Reactive or On-demand routing protocols
Proactive or Table-driven
Hybrid
Hierarchical
Geographical
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Expected Properties of Routing
Ideally an ad hoc network routing protocol
should
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be distributed in order to increase reliability
assume routes as unidirectional links
be power efficient.
consider its security
be hybrid protocols
be aware of Quality of Service
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Taxonomy
Communication model
► Multi-channel: Channel assignment using low-layer info
► Single channel model
Structure
► Are all nodes treated uniformly?
► How are distinguished nodes selected (neighbors or clusterbased)?
State information
► Is network-scale topology obtained at each node?
Scheduling
► Is route information continually maintained for each destination
(proactive or reactive)?
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DSDV
is based on the idea of Ballman-Ford routing algorithm
Every mobile station maintains a routing table that lists
► all available destinations
► the number of hops to reach the destination
► the sequence number assigned by the destination node
A station transmits its routing table
► periodically
► if a significant change has occurred in its table from the last
update sent
The routing table updates can be sent in two ways
► full dump
► incremental update
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Put figure with same illustration of DSR
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AODV
It borrows
► the basic on-demand mechanism of route discovery
and route maintenance from DSR
► the use of hop-by-hop routing, sequence numbers,
and periodic beacons from DSDV
A node periodic broadcasts he llo information to
maintain the local connectivity
It only supports the use of symmetric links
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TORA
is based on the concept of link reversal
finds multiple routes from a source node to a
destination node
the control messages are localized to a very
small set of nodes near the occurrence of a
topological change
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DSR
A node maintains route caches containing the source routes that it
is aware of
The node updates entries in the route cache as and when it le arns
about new routes
route discovery
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route request packet contains
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route reply is generated by
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the address of the source
the destination
a unique identification number
the destination
an intermediate node with current information about the destination
route maintenance
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Route error packets are generated at a node when the data link layer
encounters a fatal transmission problem
Acknowledgements, including passive acknowledgments
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OLSR
OLSR uses m ultipoint re lays to reduce
superfluous broadcast packet retransmission
and also the size of the LS packets
OLSR thus leads to efficient flooding of control
messages in the network
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OLSR (cont’d)
Only the m ultipoint re lays nodes (MPRs) need
to forward LS updates
OLSR is particularly suited for dense networks
In sparse networks, every neighbor becomes a
multipoint relay, then OLSR reduces to pure LS
protocol
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ZRP
A hybrid routing protocol that combines both
proactive and on-demand routing strategies
Each node has a predefined zone
Inside zones: proactive routing
Outside zones: on-demand routing
ZRP provides more flexibility
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Outlines
Introduction
►
►
►
►
►
What is Ad hoc networks?
Characteristic
Ad hoc vs. cellular networks
Application
Challenges
Routing Protocol
► Expected Properties of Ad-hoc Routing Protocols
► A taxonomy for routing protocols in Mobile ad
► Some common protocols (DSDV, AODV, DSR, ZRP,
TORA)
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