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Ad Hoc Networks: Ad Hoc Networks: OverviewOverview

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TextbookC. Siva Ram Murthy and B. S. Manoj, Ad Hoc

Wireless Networks: Architectures and Protocols, Prentice Hall PTR, 2004.

ReferencesCarlos de Morais Cordeiro and Dharma Prakash

Agrawal, Ad Hoc & Sensor Networks: Theory and Applications, World Scientific Publishing Co., 2006.

Feng Zhao and Leonidas Guibas, Wireless Sensor Networks: An Information Processing Approach, Elsevier, 2004.

Edgar H. Callaway, Jr., Wireless Sensor Netwoks: Architectures and Protocols, Auerbach, 2004.

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Related SitesRelated Sites

Advanced Network Technologies Division, NIST, Wireless Ad Hoc Networks,

http://w3.antd.nist.gov/wahn_home.shtml Autonomous Networks Research Group, USC

WSN bibliography, http://ceng.usc.edu/~anrg/SensorNetBib.html

IETF MANET WG http://www.ietf.org/html.charters/manet-charter.html

IEEE 802 WG http://grouper.ieee.org/groups/802/dots.html

Zigbee http://www.zigbee.org

TinyOS http://www.tinyos.net/

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Wireless Network TechnologyWireless Network Technology

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Internet

WLAN

Cellular

[Mobile/Wireless] Ad Hoc Networks

Wireless NetworksWireless Networks

Wireless Networks Infrastructured Network

• Cellular Network (3GPP or 3GPP2)• Wireless LAN (IEEE 802.11)

Infrastructureless Network• Ad Hoc Network

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Ad Hoc Networks vs. …Ad Hoc Networks vs. …

Ad hoc networks vs. Wireless mobile networks Infrastructureless vs. Infrastructured Network All devices of an ad hoc network are likely to have

similar constraints Ad hoc networks vs. Peer-to-peer networks

P2P devices use existing networked structures such as Internet

All P2P networks are not ad hoc network • Because NOT all ad hoc network utilize an existing

structure for the communication among devices Ad hoc computing vs. Pervasive computing

The devices for pervasive computing are usually very small and can be embedded in any type of objects

• Users are sometimes not even aware of the existence of the embedded electronic chips

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Ad hoc networks (1)Ad hoc networks (1) Temporary network composed of mobile

nodes without preexisting communication infrastructure, such as Access Point (AP) and Base Station (BS). Each node plays the role of router for multi-hop routing.

Self-organizing network without infrastructure networks Started from DARPA PRNet in 1970

Cooperative nodes (wireless) Each node decode-and-forward packets for other nodes

Multi-hop packet forwarding through wireless links Proactive/reactive/hybrid routing protocols

Most works based on CSMA/CA to solve the interference problem IEEE 802.11 MAC

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Ad hoc networks (2)Ad hoc networks (2)

But, there is no links Nodes simply radiate energy

Nodes can be cooperative in many other ways (complex) Amplify and forward interference cancellation to increase SINR

There may be many things out there that we can take advantage of across layers for improvement!

F

D

E

C

A

B

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Ad Hoc Network (3)Ad Hoc Network (3)

Ad hoc networks

Mobile ad hoc networks(MANETs)

Wirelss Mesh Networks(WMN)

Wireless sensor networks

The application areas, the security requirements and the constraints of the single devices differ …

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Cellular Net vs. Ad Hoc Net (1)Cellular Net vs. Ad Hoc Net (1)

Cellular Net Ad Hoc Net

Fixed infrastructure-based Infrastruxture-less

1-hop wireless links Multi-hop wireless links

Guaranteed bandwidth Shared radio channel

Centralized routing Distributed routing

Seamless connectivityFrequent path breaks due to mobility

High cost and time of deployment

Quick and cost-effective deployment

Frequency reuse through geographical channel reuse

Dynamic frequency reuse based on CSMA

Time sync: easier to achieve. Difficult and consume BW

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Cellular Net vs. Ad Hoc Net (2)Cellular Net vs. Ad Hoc Net (2)

Cellular Net Ad Hoc Net

BW reservation: easier Requires complex MAC

App. Domain: civilian and commercial sector

Battlefields, emergency operations, collaborative computing

High cost of net maintenanceSelf-organization and maintenance is built into net

MHs: low complexity More intelligence

Major goal of routing: max call acceptance, min call drop

Find paths with min overhead, quick reconfiguration of broken paths

Widely deployed

Several issues are to be addressed for commercial deployment,Widespread use in defense

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Major ApplicationsMajor Applications

Military Emergency Service Collaborative and Distributed

Computing Wireless Mesh Network Wireless Sensor Network Telematics Wireless Personal Area Network Home Network Ad Hoc Relay for Cellular Network Networks for ubiquitous computing

Demands for group

communications

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MilitaryMilitary

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Emergency Service Emergency Service

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MANET – Research TargetMANET – Research Target

MANET No infrastructure Self organizing

networks Communications via

mobile nodes Dynamic topology Heterogeneity

bandwidth-constrained variable-capacity links

Limited physical security

Nodes with limited battery life and storage capabilities

Issues in MANET Ad Hoc Unicast Routing Ad Hoc

Multicast/Broadcast Routing

Power Saving Global Connectivity for

MANET Addressing & DNS

Service Automatic Support of

Networking in MANET• MANET

Autoconfiguration

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Wireless Mesh NetworksWireless Mesh Networks

Mesh network implemented over WLAN

Industrial standards Activities IEEE 802.11, IEEE 802.15, IEEE 801.16 have

established sub-working groups to focus on new standards for WMNs

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WMN ArchitectureWMN Architecture

WMNs (Wireless Mesh Networks) consist of: mesh routers and mesh clients

Mesh routers Conventional wireless AP (Access Point) functions Additional mesh routing functions to support multi-hop

communications Usually multiple wireless interfaces built on either the

same or different radio technologies Mesh clients

Can also work as a router for client WMN Usually one wireless interface

Classification of WMN architecture Infrastructure/Backbone WMNs Client WMNs Hybrid WMNs

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Infrastructure/backbone Infrastructure/backbone WMNsWMNs

Internet

Wi-FiNetworks

CellularNetworks WiMAX

Networks

SensorNetworksBase Station

Sink nodeSensor

Wireless MeshBackbone

Wired ClientsMesh RouterMesh Router

with GatewayMesh Routerwith Gateway

Mesh Routerwith Gateway/Bridge

Mesh Routerwith Gateway/Bridge

Mesh Routerwith Gateway/Bridge

Access Point

Base Station

Mesh Routerwith Gateway/Bridge

Wireless Clients

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Client WMNsClient WMNs

Mesh Client

Mesh Client

Mesh Client

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Hybrid WMNsHybrid WMNs

Wi-Fi, Wi-MAX,Sensor Networks,

Cellular Networks, etc.

Internet

Wireless Mesh Clients

Wireless MeshBackbone

Conventional Clients

Mesh Router

Mesh Router

Mesh Routerwith Gateway

Mesh Routerwith Gateway

Mesh Routerwith Gateway/Bridge

Mesh Router Mesh Router

Mesh Routerwith Gateway/Bridge

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Sensor Network ModelSensor Network Model

Source

Stimulus

Sink

Sink

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Wireless Sensor NetworksWireless Sensor Networks

A sort of ad-hoc networks A network of low cost,

densely deployed,untethered sensor nodes

Application areas:heath, military, and home

Placed in inaccessible terrains or disaster areas It may be impossible to recharge batteries

Different Node Characteristics from Traditional nodes # of nodes in a sensor network can be several orders of

magnitude higher than the nodes in an Ad Hoc network (100s to 1000s nodes)

Densely deployed (20 nodes/m3) Prone to failures Topology changes very frequently Mainly use a broadcast communication, whereas most Ad Hoc

networks are based on point-to-point Limited in power, computing capacities, and memory May not have global ID because of the large amount of

overhead and large number of sensors

Ad Hoc NetAd Hoc Net

Wireless Wireless Sensor Sensor NetworkNetwork

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Existing Wireless Net vs. Sensor Existing Wireless Net vs. Sensor NetNetCellular system Bluetooth,

MANETSensor Network

Single Hop Multi-hop Multi-hop

High QOSBandwidth efficiency

High QOS Power conservation

Limited bandwidthLarge number of nodeNarrow radio range

Frequent topology change

Station to Base station

Peer to peerPeer to multi node

Peer to multi node

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Sensor Networks ArchitectureSensor Networks Architecture

Sensor node Made up of four basic components

• Sensing unit, Processing unit, Transceiver unit, and Power unit

Additional application-dependent components• Location finding system, power generator, and

mobilizer Scattered in a sensor field Collect data and route data back to the sink

Sink Communicate with the task manager node

(user) via Internet or satellite

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Challenges in Ad Hoc NetworksChallenges in Ad Hoc Networks

Limited wireless transmission range Broadcast nature of the wireless

medium Packet losses due to transmission errors Mobility-induced route changes Mobility-induced packet losses Battery constraints Potentially frequent network partitions Ease of snooping on wireless

transmissions (security hazard)

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Issues in Ad Hoc NetworksIssues in Ad Hoc Networks

Medium access scheme Routing Multicasting Transport layer protocol Pricing shceme QoS provisioning Security Energy management Addressing and service discovery Scalability Deployment considerations

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Medium Access SchemeMedium Access Scheme Distributed operation Synchronization Hidden terminal problem Exposed terminal problem Throughput Access delay Fairness: especially for relaying nodes Real-time traffic support Resource reservation Ability to measure resource availability Capability for power control Adaptive rate control Use of directional antennas

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Routing (1)Routing (1)

ChallengesMobility

• results in path breaks, packet collisions, transient loops, stale routing information, and difficulty in resource reservation

BW constraintsError-prone and shred channel

• BER: 10-5 ~ 10-3 wireless vs. 10-12 ~ 10-9 wiredLocation-dependent contention

• Distribute load uniformly

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Routing (2)Routing (2)

RequirementsMinimum route acquisition delayQuick route reconfigurationLoop-free routingDistributed routing approachMinimum control overheadScalabilityQoS provisioningSupport for time-sensitive trafficSecurity and privacy

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MulticastingMulticasting

Robusteness recover and reconfigure quickly from potential

mobility-induced link breaksEfficiencyMin control overheadQoS supportEfficient group managementScalabilitysecurity

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Transport Layer ProtocolsTransport Layer Protocols

UDP No congestion control congestion increase

contention degrade throughput TCP: major performance degradation due to

Frequent path break route reconfiguration RTO ReTx/CC low

throughput Stale routing information

• Increase out-of-order packets dup ACKs CC High channel error rate

• Loss of data/ACK ACK is delayed RTO CC Frequent network partition

• All the packets dropped RTO/multiple ReTx increase RTO/CC

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SecuritySecurity

DoS attack Resource consumption

Energy depletionBuffer overflow

Host impersonation Information disclosure Interference

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Energy ManagementEnergy Management

Tx power mgmtMAC: sleep modeRouting: consider battery life time: load

balancingTransport: reduce ReTxApp

Battery energy mgmtExtend battery life by taking adv of chemical

properties, discharge patterns, and by the selection of a battery from a set of batteries

Processor power mgmt Device power mgmt

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Deployment Consideration (1)Deployment Consideration (1)

Adv. in ad hoc netLow cont of deployment Incremental deplymentShort deplyment timeReconfigurablity

Scenario of deploymentMilitary deployment: data-centric or user-

centricEmergency operation deployment: hend-held,

voice/data, < 100 nodesCommercial wide-area deployment: e.g. WMNHome network deplyment

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Deployment Consideration (2)Deployment Consideration (2)

Required longevity of network Area of coverage Service availability: redundancy Operational integration with other

infrastructure Satellite network, UAV(unmanned aerial vehicles), GPS Cellular network

Choice of protocols TDMA or CSMA-based MAC? Geographical routing (using GPS) Power-saving routing ? TCP extension ?