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Chpter-01Ad hoc Networks: Introduction, Issues in Ad hoc wireless networks, Ad hoc

wireless internet.

Introduction

Darius I (522 486 BC), the king of Persia, devised an innovative communication systemthat was used to send messages and news from his capital to the remote provinces of

his empire by means of line of shouting men positioned on tall structures or heights.

This system was more than 25 times faster than normal messengers available at that

time.

In 1970, Norman Abramson and his fellow researchers at University of Hawaii inventedALOHAnet, an innovative communication system for linking together the universities ofHawaiian Islands. It utilized single hop wireless packet switching and a multiple access

solution for sharing a single channel. The basic idea behind ALOH Anet was compelling

and applicable to any environment where access to a common resource had to be

negotiated among a set of uncoordinated nodes.

The success and novelty of ALOHAnet triggered a widespread interest in differentdirections of computer communication, including the work that led to the development

of Ethernet by Robert Metcalfe and the Packet Radio Network (PRNET) project

sponsored by the Defence Advanced Research Projects Agency (DARPA).

PRNET used a combination of ALOHA and Carrier Sense Multiple Access (CSMA) foraccess to shared radio channel. The radio interface employed the direct sequence (DS)spread spectrum scheme. The system was designed to self organize, self configure and

detect radio connectivity from dynamic operation of a routing protocol without any

support from fixed infrastructure.

The successful demonstration of PRNET proved feasibility and efficiency ofinfrastructure less networks and their applications, but faced issues including those of

obtaining, maintaining and utilizing topology information, error and flow control over

wireless links, reconfigurations of paths to handle path breaks arising due to the

mobility of nodes and routers, processing and storage capability of nodes, and

distributed channel sharing.

DARPA extended the work on the multi hop wireless networks through the survivableradio network (SURAN) project that aimed at providing ad hoc networking with small,low cost, low power devices with efficient protocols and improved scalability and

survivability.

Realizing the necessity of open standards, a working group within Internet EngineeringTask Force (IETF), termed the Mobile Ad Hoc Networks (MANET) working group, was

formed to standardize the protocols and functional specifications of Ad hoc networks.


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The vision of IETF effort in MANET working group is to provide improved standardized

routing functionality to support self organizing mobile networking infrastructure.

In 1994, the Swedish communication equipment maker Ericsson proposed to develop ashort range, low power, low complexity, and inexpensive radio interface and associated

communication protocols referred to as Bluetooth for ubiquitous connectivity among

heterogeneous devices. This effort was later taken over by a Special Interest Group (SIG)formed by several computer and telecommunication vendors such as 3Com, Ericsson,

IBM, Intel, Lucent, Microsoft, Motorola, Nokia and Toshiba. The Bluetooth SIG aims at

delivering a universal solution for connectivity among heterogeneous devices.

Bluetooth standardizes the single hop point to point wireless link that helps inexchanging voice or data, and formation of piconets that are formed by a group of

nodes in a smaller geographical region where every node can reach every other node in

a group within a single hop. Multiple piconets can form a scatternet, which

necessitates the use of multi hop routing protocols.

Recent advances in wireless network architecture reveal interesting solutions thatenable the mobile ad hoc nodes to function in presence of infrastructure. Multi hop

cellular networks (MCNs) and self organizing Packet Radio Ad hoc Networks with

Overlay (SOPRANO) are examples of such type of networks. This hybrid architecture

improves the capacity of the system significantly.

Cellular and Ad Hoc Wireless Networks

The current cellular wireless networks are classified as the infrastructure dependentnetworks. The path setup for a call between two nodes is completed through the base

station.

Ad hoc wireless networks are defined as the category of wireless networks that utilizemulti hop radio relaying and are capable of operating without the support of the fixedinfrastructure. Hence, they are called infrastructure less networks.

The path setup for a call between two nodes is completed through intermediate mobilenode.

Wireless mesh networks and wireless sensor networks are example of ad hoc wirelessnetwork.

The presence of base stations simplifies routing and resource management in a cellularnetwork as the routing decisions are made in a centralized manner with more

information about the destination node.

But in ad hoc wireless network, the routing and resource management are done in adistributed manner in which all nodes co ordinate to enable communication among

them. This requires each node to be more intelligent so that it can function both as a

network host for transmitting and receiving data and as a network router for routing

packets from other nodes. Hence, mobile node in ad hoc networks are more complex

than cellular networks


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Differences between cellular networks and ad hoc wireless networks

Cellular Networks Ad Hoc Wireless Networks

Fixed infrastructure-based Infrastructure-less

Single-hop wireless links Multi-hop wireless links

Guaranteed bandwidth (designed for voice traffic) Shared radio channel (more suitable for best-effort data

traffic)

Centralized routing Distributed routing

Circuit-switched (evolving toward packet switching) Packet-switched (evolving toward emulation of circuit

switching)

Seamless connectivity (low call drops during handoffs) Frequent path breaks due to mobility

High cost and time of deployment Quick and cost-effective deployment

Reuse of frequency spectrum through geographical channel

reuse

Dynamic frequency reuse based on carrier sense

mechanism

Easier to achieve time synchronization Time synchronization is difficult and consumes bandwidth

Easier to employ bandwidth reservation Bandwidth reservation requires complex medium accesscontrol protocols

Application domains include mainly civilian and commercial

sectors

Application domains include battlefields, emergency

search and rescue operations, and collaborative computing

High cost of network maintenance (backup power source,

staffing, etc.)

Self-organization and maintenance properties are built

into the network

Mobile hosts are of relatively low complexity Mobile hosts require more intelligence (should have a

transceiver as well as routing/switching capability)

Major goals of routing and call admission are to maximize

the call acceptance ratio and minimize the call drop ratio

Main aim of routing is to find paths with minimum

overhead and also quick reconfiguration of broken paths

Widely deployed and currently in the third generation of

evolution

Several issues are to be addressed for successful

commercial deployment even though widespread use

exists in defence.


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Differences between cellular networks and ad hoc wireless networks

Cellular Networks Ad Hoc Wireless Networks

Applications of Ad Hoc Wireless Networks

Military Applications

Ad Hoc wireless networks can be very useful in establishing communication among agroup of soldiers for tactical operations. Setting up a fixed infrastructure for

communication among group of soldiers in enemy territories or in inhospitable terrains

may not be possible. In such environments, ad hoc wireless networks provide the

required communication mechanism very quickly.

Another application in this area can be the coordination of military objects moving inhigh speeds such as fleets of airplanes or warships. Such applications require quick and

reliable communication.

Secure communication is of prime importance as eavesdropping or other securitythreats can compromise the purpose of communication or the safety of personnel

involved in these tactical operations. They also require the support of reliable and

secure multimedia multicasting. As the military applications require very secure communication, the vehicle mounted

nodes can be assumed to be very sophisticated and powerful. They can have multiple

high power transceivers, each with the ability to hop between different frequencies for

security reasons. Such communication systems can be assumed to be equipped with

long life batteries that might not be economically viable for normal usage.


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They can even use other services like location tracking (using GPS) or other satellitebased services for efficient communication and co ordination. Resource constraints such

as battery life and transmitting power may not exist in certain types of applications of

ad hoc wireless networks.

The primary nature of communication required in military environment enforcesreliability, efficiency, secure communication and support for multicast routing.

Collaborative and Distributed Computing

In collaborative computing, the requirement of a temporary communicationinfrastructure for quick communication with minimal configuration among a group of

people in a conference or gathering necessitates the formation of an ad hoc wireless

network.

Consider a group of researchers who want share their research findings or presentationsduring a conference, or a lecturer distributing notes on fly. In such cases, the formation

of ad hoc wireless networks with the support for reliable multicast routing can serve the

purpose. The distributed file sharing does not require the great level of security, but it

requires reliability of data transfer.

Consider a node that is part of ad hoc wireless network has to distribute a file othernodes in the network. The goal of the transmission is that all the desired receivers must

have the replica of the transmitted file, but does not demand the communication to be

interruption free.

Other applications such as streaming of multimedia objects among participating nodesmay require support for soft real time communication. The users of such applications

prefer economical and portable devices, usually powered by battery sources. Hence, a

mobile node may drain its battery and can have varying transmission power, which may

result in unidirectional links with its neighbours. Devices used for such applications will be laptops with wireless interface cards, personal

digital assistants (PDAs) or mobile devices with high processing power. In presence of

heterogeneity, interoperability is an important issue.

Emergency Operations

Ad hoc networks are useful in emergency operations such as search and rescue, crowdcontrol and commando operations.

The major factors that favours for such tasks are self configuration of the system withminimal overhead, independent of fixed or centralized infrastructure, the nature of the

terrain of such applications, the freedom and flexibility of mobility, and theunavailability of communication infrastructure.

Since ad hoc networks require minimum initial network configuration for theirfunctioning, very little or no delay is involved in making the network fully operational.

Ad hoc wireless networks employed in emergency operations should be distributed andscalable to large number of nodes. They should be able to provide fault tolerant

communication paths.


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Wireless Mesh Network

Wireless mesh network are ad hoc wireless networks that are formed to provide analternate communication infrastructure for mobile or fixed nodes, without the spectrum

reuse constraints and the requirements of network planning of cellular networks.

The mesh topology of wireless mesh networks provide many alternate paths for a datatransfer session between source and destination, resulting in quick reconfiguration of

the path when the existing path fails due to node failure.

The infrastructure built is in form of small radio relaying devices fixed on the roof tops ofthe houses in a residential zones or similar devices fitted on lamp posts.

The investment required in wireless mesh networks is much less than what is requiredfor the cellular network counterparts. Such networks are formed by placing wireless

relaying equipment spread across the area covered by the network.

The possible deployment scenarios of wireless mesh networks include residential zones,highways, business zones, important civilian regions, and university campuses.

Wireless mesh network should be capable of self organization and maintenance. Theability of the network to overcome single or multiple node failure resulting from

disasters, makes it convenient for providing the communication infrastructure for

strategic applications.

The major advantages include support for a high data rate, quick and low cost ofdeployment, enhanced services, high scalability, easy extendibility, high availability, and

low cost per bit.

Mesh network operates at a license free ISM band around 2.4 GHz to 5 GHz and datarate of 5 Mbps to 60 Mbps, depending on technology used for physical layer and MAClayer.

The deployment time required for this network is much less than compared to othernetwork. Incremental deployment or partial batch deployment can also be done.

Mesh network scale well to provide support to large number of nodes. Even at a veryhigh density of mobile nodes, by employing power control at mobile nodes and relay

nodes, better system throughput and support for a large number of users can be

achieved.


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Partial roll out and commissioning of network and extending the service in a seamlessmanner without affecting the existing installation are benefits from the viewpoint of

service providers.

These networks provide very high availability compared to the existing cellulararchitecture, where the presence of fixed base station involves the risk of a single point

failure.

Wireless Sensor Networks

These are a special category of ad hoc wireless networks that are used to provide awireless communication infrastructure among the sensors deployed in a specific

application domain.

Sensor nodes are tiny devices that have the capability of sensing the physicalparameters, processing the data gathered, and communicating over the network to the

monitoring station.

A sensor network is a collection of a large number of sensor nodes that are deployed ina particular region. The activity of sensing can be periodic or sporadic.

An example for periodic sensing is the sensing of environmental factors for themeasurement of parameters such as temperature, humidity and nuclear radiations.

An example for sporadic sensing is detecting border intrusion, sensing the temperatureof the furnace to prevent it rising beyond the threshold, measuring the stress on critical

structures or machinery.

The issues that make sensor networks a distinct category of ad hoc wireless networksare as follows:

Mobility of nodes Sensor networks need not in all cases be designed to support mobility of

sensor nodes. For example, the nodes deployed for periodic monitoring of soil

properties are not required to be mobile. The sensor nodes that are fitted

in bodies of patient in post surgery ward may be designed to support

limited or partial mobility.

Size of network The number of nodes in a sensor network can be much larger than a

typical ad hoc wireless network.

Density of deployment The density of nodes varies with the domain of application. Military

applications require high availability of the network, making redundancy

a high priority.

Power constraints The power constraint is more stringent than in ad hoc wireless networks. Sensor nodes are expected to work in harsh environmental or

geographical conditions, with minimum or no human supervision and

maintenance.


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Running such a network, with nodes powered by a battery source withlimited energy, demands efficient protocol.

The power sources in ad hoc wireless networks can be classified in threecategories:

Replenishable power sources: The power sources can be replacedwhen existing source is fully drained. Eg: Wearable sensors thatare used to sense body parameters.

Non replenishable power sources: The power sources cannot bereplenished once the network has been deployed. The

replacement of the sensor node is the only solution. Eg:

Deployment of sensor nodes in a remote, hazardous terrain.

Regenerative power sources: These have the capability ofregenerating power from the physical parameter under

measurement. Eg: The sensor employed for sensing temperature

at a power plant can use power sources that can generate power

by using appropriate transducers.

Data/information fusion The limited bandwidth and power constraints demand aggregation of bits

and information at the intermediate relay nodes that are responsible for

relaying.

Data fusion refers to the aggregation of multiple packets into one beforerelaying it. The main aim is to reduce the bandwidth consumed by

redundant headers of the packets and reducing the media access delay

involved in transmitting multiple packets.

Information fusion aims at processing the sensed data at theintermediate nodes and relaying the outcome to the monitor node.

Traffic distribution The communication traffic pattern varies with the domain of application

in sensor networks.

For Example, the environmental sensing application generates shortperiodic packets indicating the status of the environmental parameters

under observation to a central monitoring station. This kind of traffic

demands low bandwidth.

But, ad hoc wireless networks generally carry user traffic such as digitizedand packetized voice stream or data traffic, which demands higher

bandwidth.

Hybrid Wireless Network

Hybrid wireless architecture includes multi hop cellular networks and integratedcellular ad hoc relay networks.

The primary concept behind cellular network is geographical channel reuse. Cellsectoring, cell resizing and multi tier cells have been proposed to increase the capacity

of cellular network.


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The capacity of a cellular network can be increased if the network incorporates theproperties of multi hop relaying along with the support of existing fixed infrastructure.

MCNs combine the reliability and support of fixed base stations of cellular networkswith flexibility and multi hop relaying of ad hoc wireless networks.

When two nodes in the same cell want to communicate with each other, the connectionis routed through multiple wireless hops over the intermediate nodes. The base station

maintains the information about the topology of the network for efficient routing. The

base station may or may not be involved in this multi hop path.

Hybrid wireless networks can provide high capacity resulting in lowering the cost ofcommunication to less than that in single hop cellular networks.

The major advantages of hybrid wireless networks are as follows Higher capacity than cellular networks obtained due to the better channel reuse

provided by reduction of transmission power, as mobile nodes use a power

range that is a fraction of the cell radius.

Increased flexibility and reliability in routing. The flexibility in terms of selectingthe best suitable nodes for routing. The increased reliability in terms of resilience

to failure of base stations, in which case a node can reach other nearby base

stations using multi hops paths.

Better coverage and connectivity in holes of a cell can be provided by means ofmultiple hops through intermediate nodes in the cell.

Issues in Ad Hoc Wireless Networks

The major issues that affect the design, deployment and performance of ad hoc wirelesssystems are as follows

Medium access scheme Routing


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Multicasting Transport layer protocol Pricing scheme Quality of service provisioning Self organization Security Energy Management Addressing and service discovery Scalability Deployment considerations

Medium Access Scheme

The primary responsibility of MAC protocol in ad hoc wireless networks is thedistributed arbitration for the shared channel for transmission of packets.

The major issues to be considered in designing a MAC protocol for ad hoc wirelessnetworks are as follows:

Distributed Operations The ad hoc wireless networks need to operate in environment where no

centralized co ordination is possible.

The MAC protocol design should be fully distributed involving minimalcost overhead.

Synchronization The MAC protocol design should take into account the requirement of

time synchronization. Synchronization is mandatory for TDMA based

systems for management of transmission and reception slots.

Synchronization involves usage of scarce resources such as bandwidthand battery power. The control packets used for synchronization can also increase collisions

in network.

Hidden Terminals Hidden terminals are nodes that are hidden from the sender of a data

transmission session, but are reachable to the receiver of the session. In

such cases, hidden terminals can cause collisions at the receiver node.

The hidden terminals can significantly reduce the throughput of a MACprotocol used in ad hoc wireless networks. Hence, the MAC protocol

should be able to alleviate the effects of hidden terminals.

Exposed Terminals The nodes that are in the transmission range of the sender of an ongoing

session are prevented from making a transmission.

The exposed node should be allowed to transmit in a controlled fashionwithout causing collision to the ongoing data transfer.

Throughput


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The MAC protocols should attempt to maximize the throughput of thesystem.

The important consideration for throughput enhancement are minimizingthe occurrence of collisions, maximizing the channel utilization, and

minimizing the control overhead.

Access Delay The access delay refers to the average delay that any packet experiences

to get transmitted.

The MAC protocol should attempt to minimize the delay. Fairness

Fairness refers to ability of MAC protocol to provide an equal share orweighted share of the bandwidth to all competing nodes.

It can be either node based or flow based. Node based provide an equal bandwidth share for competing nodes. Flow based provide an equal share for competing data transfer

sessions.

Fairness is important due to multi hop relaying done by nodes. An unfair relaying load of node results in draining the resources much

faster than other nodes.

Real time traffic support Environment without any central co ordination, with limited

bandwidth, and with location dependent contention, supporting time

sensitive traffic such as voice and video requires explicit support from

MAC protocol.

Resource reservation The provisioning of QoS defined by parameters such as bandwidth, delay,

and jitter requires reservation of resources such as bandwidth, bufferspace and processing power.

The inherent mobility of nodes makes such reservation of resources adifficult task.

A MAC protocol should be able to provide mechanism for supportingresource reservation and QoS provisioning.

Ability to measure resource availability The MAC protocol should be able to provide an estimation of resource

availability at every node, in order to handle resources such as bandwidth

and perform call admission control based on their availability.

Capability of power control The transmission power control reduces the energy consumption at

nodes, causes a decrease in interference at neighbour nodes, and

increase frequency usage.

Support for power control in MAC layer is important in ad hocenvironment.

Adaptive rate control The variation in data bit rate achieved over a channel.


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A MAC protocol that uses adaptive rate control can make use of a highdata rate when sender and receiver are nearby and adaptively reduce the

data rate as they move away from each other.

Use of directional antennas Advantages include increased spectrum reuse, reduction in interference,

and reduced power consumption. Most of the existing MAC protocols that use omnidirectional antennas do

not work with directional antennas.

Routing

The responsibilities of routing includes exchanging the route information; finding a feasible path to a destination based on criteria such as hop length,

minimum power required and life time of wireless link;

gathering information about path breaks; mending the broken paths expending the minimum processing power and

bandwidth;

utilizing minimum bandwidth; The major challenges that a routing protocol faces are as follows

Mobility The mobility of nodes results in frequent path breaks, packet collisions,

transient loops, state routing information and difficulty in resource

reservation.

A good routing protocol should be able to efficiently solve all theseissues.

Bandwidth Constraint Since the channel is shared by all nodes in the broadcast region, thebandwidth available per wireless link depends on the number of nodes

and the traffic they handle.

Thus only a fraction of the total bandwidth is available for every node. Error prone and shared channel

The bit error rate in wireless channel is very high compared to that in itswired counterparts. A routing protocol must take this into consideration.

Consideration of the state of the wireless link, signal to noise ratio,and path loss for routing in ad hoc wireless networks can improve the

efficiency of the routing protocol.

Location dependent contention The load on the wireless channel varies with the number of nodes

present in a given geographical region. This makes the contention of the

channel high when the number of nodes increases.

The high contention of channel results in a high number of collisions anda subsequent wastage of bandwidth.


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A good routing protocol should have built in mechanisms fordistributing the network load uniformly across the network so that

formations of regions where channel contention is high can be avoided.

Other resource constraints Computing power, battery power and buffer storage also limit the

capability of a routing protocol. The major requirements of a routing protocol in ad hoc wireless networks are the

following:

Minimum route acquisition delay The route acquisition delay for a node that does not have a route to a

particular destination node should be minimal as possible.

This delay might vary with the size of the network and the network load. Quick route reconfiguration

The routing protocol should be able to quickly perform routereconfiguration in order to handle path breaks and subsequent packet

losses.

Loop free routing Due to random movement of nodes, transient loops may form in the

route established. A routing protocol should detect such transient routing

loop and take corrective actions.

Distributed routing approach An ad hoc wireless network is fully distributed wireless network and use

of centralized routing approach in such a network may consume a large

amount of bandwidth.

Minimum control overhead The control packets exchanged for finding the new route and maintaining

the existing route should be kept as minimal as possible. The control packets consume precious bandwidth and can cause

collisions with the data packets, thereby reducing the network

throughput.

Scalability Scalability is the ability of the routing protocol to scale well in a network

with large number of nodes.

This requires minimization of control overhead and adaptation of therouting protocol to the network size.

Provisioning of QoS

The routing protocols should be able to provide the QoS as demanded bythe nodes or the category of calls.

The QoS parameters can be bandwidth, delay, jitter, packet delivery ratio,and throughput.

Support for time sensitive traffic Tactical communications and similar applications require support for time

sensitive traffic.


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The routing protocol should be able to support both hard real time andsoft real time traffic.

Security and privacy The routing protocol in ad hoc wireless networks must be resilient to

threats and vulnerabilities.

It must have inbuilt capability to avoid resource consumption, denial ofservice, impersonation and similar attacks possible against an ad hoc

wireless network.

Multicasting

Nodes form group to carry out certain tasks that require point to multipoint andmultipoint to multipoint voice and data communication.

The arbitrary movement of nodes changes the topology dynamically in an unpredictablemanner.

The mobility of nodes, with the constraints of power source and bandwidth, makesmulticast routing challenging.

Providing of multiple links among the nodes in an ad hoc network results in a mesh shaped structure. The mesh based multicast routing structure may work well in a high

mobility environment.

The major issues in designing multicast routing protocols are as follows Robustness

The multicast routing protocol must be able to recover and reconfigurequickly from potential mobility induced link breaks thus making it

suitable for use in highly dynamic environments.

Efficiency A multicast protocol should make a minimum number of transmissions todeliver a data packet to all the group members.

Control overhead The scarce bandwidth availability demands minimal control overhead for

the multicast session.

Quality of service QoS is essential in multicast routing because the data transferred in

multicast session is time sensitive.

Efficient group management Group management refers to the process of accepting multicast session

members and maintaining the connectivity among them until the session

expires.

This need to be performed with minimal exchange of control messages. Scalability

The multicast routing protocol should be able to scale for a network witha large number of nodes.

Security


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Authentication of session members and prevention of non membersfrom gaining unauthorized information play a major role in military

communication.

Transport Layer Protocols

The main objective of the transport layer protocols include setting up and maintainingend to end connections, reliable end to end delivery of data packets, flow control

and congestion control.

The usage of connection less transport layer protocols (UDP) increases the contention ofthe already chocked wireless links. For example, in a network that employs a contention

based MAC protocol, nodes in a high contention region experience several back off

states, resulting in an increased number of collisions and a high latency. Connectionless

transport layer protocols, unaware of this situation, increase the load in the network,

degrading the network performance.

The major performance degradation faced by a reliable connection oriented transportlayer protocol such as TCP, arises due to frequent path breaks, presence of stale routing

information, high channel error rate and frequent network partitions.

Due to the mobility of nodes and limited transmission range, an existing path to adestination node experiences frequent path breaks. Each path break results in route

reconfiguration that depends on the routing protocol employed.

The process of finding an alternate path or reconfiguring the broken path might takelonger than the retransmission time out of the transport layer at the sender, resulting in

retransmission of packets and execution of congestion control algorithm, which

decreases the size of congestion window, resulting in low throughput.

In an environment where path breaks are frequent, the execution of congestion controlalgorithms on every path break affects the throughput drastically.

The latency associated with the reconfiguration of a broken path and the use of routecache results in stale route information at the nodes. Hence, packets will be forwarded

through multiple paths to a destination, causing an increase in number of out of

order packets.

Multipath routing protocols such as temporally ordered routing algorithm (TORA) andsplit multipath routing (SMR) protocols employ multiple paths between a sources

destination pair.

Out of order packet arrivals force the receiver of the TCP connection to generateduplicate ACKs. On receiving duplicate ACKs, the sender invokes the congestion control

algorithm.

Wireless channels are inherently unreliable due to the high probability of errors causedby interference. In addition to the error due to the channel noise, the presence of

hidden terminals also contributes to the increased loss of TCP data packets or ACK.

When the TCP ACK is delayed more than the round trip timeout, the congestion control

algorithm is invoked.

Due to the mobility of the nodes, ad hoc networks frequently experience isolation ofnodes from rest of the network or occurrences of partition in the network. If sender and


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receiver are in two different partitions, all the packets get dropped. This tends to be

more serious when the partitions exist for a long duration resulting in multiple

retransmissions of the TCP packets and subsequent increase in retransmission timers.

Pricing Scheme

An ad hoc networks functioning depends on the presence of relaying nodes and theirwillingness to relay other nodes traffic.

Even if the nodes density is sufficient enough to ensure a fully connected network, arelaying neighbour node may not be interested in relaying a call and may decide to

power down.

The non optimal path consumes more resources and affects the throughput of thesystem.

As the intermediate nodes in a path that relay the data packets expend their resourcessuch as battery charge and computing power, they should be properly compensated.

Hence prising scheme that incorporates service compensation or service

reimbursements is required.

Quality of Service Provisioning

QoS is the performance level of services offered by a service provider or a network tothe user.

QoS provisioning often requires negotiation between the host and the network,resource reservation schemes, priority scheduling, and call admission control.

Rendering QoS in ad hoc wireless networks can be per flow, per link or per node basis.In ad hoc networks, the boundary between the service provider and the user is blurred,

thus making essential to have better coordination among the hosts to achieve QoS.

QoS parameters As different applications have different requirements, their level of QoS and

associated parameters differ from application to application.

For multimedia applications, the bandwidth and delay are the key parameters,whereas, the military applications have the additional requirements of security

and reliability.

For defence applications, finding trustworthy intermediate hosts and routingthrough them can be QoS parameters.

For applications such as emergency search and rescue operations, availabilityis the key QoS parameter. Applications for hybrid wireless networks can have maximum available link life,

delay, channel utilization and bandwidth as the key parameters for QoS.

Applications such as sensor networks require that the transmission among themresults in minimum energy consumption; hence battery life and energy

conservation can be the prime QoS parameters.

QoS aware routing


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The QoS aware routing protocol should have the routing use QoS parameters forfinding a path.

The parameters that can be considered for routing decisions are networkthroughput, packet delivery ratio, reliability, delay, delay jitter, packet loss rate,

bit error rate and path loss.

Decisions on the level of QoS and the related parameters for such services areapplication specific and are to be met by the underlying network.

In the case where the QoS parameter is bandwidth, the routing protocol utilizesthe available bandwidth at every link to select a path with necessary bandwidth.

This also demands the capability to reserve the required amount of bandwidth

for that particular connection.

QoS framework A QoS framework is a complete system that attempts to provide the promised

services to each user or application. All the components within this subsystem

cooperate in providing the required services.

The key component of QoS framework is a QoS service model which defines theway user requirements are served. The key design issue is whether to serve the

user on a per session basis or a per class basis. Each class represents an

aggregation of users based on certain criteria.

The other key component of this framework are QoS routing to find all or some feasible path in the network QoS signalling for resource reservation QoS media access control Connection admission control scheduling schemes pertaining to the service model

The QoS modules such as routing protocol, signalling protocol and resourcemanagement should react promptly according to the changes in the networkstate and flow state.

Self Organization

Ad hoc wireless network should exhibit organizing and maintaining the network byitself.

The major activities include neighbour discovery, topology organization and topologyreorganization.

During the neighbour discovery phase, every node in the network gathers informationabout its neighbours and maintains that information in appropriate data structure. This

may require periodic transmission of short packets named beacons or promiscuous

snooping on the channel for detecting activities of neighbours.

In topology organization phase, every node in the network gathers information aboutthe entire network or part of the network in order to maintain topological information.

During the topology reorganization phase, the ad hoc require updating the topologyinformation by incorporating the topological changes occurred in the network due to


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the mobility of nodes, failure of nodes or complete depletion of power sources of the

nodes.

The reorganization consists of two major activities. First is the periodic and aperiodicexchange of topological information. Second is the adaptability.

Network partitioning and merging of two existing partitions requires major topologicalreorganization.

Ad hoc wireless networks should be able to perform self organization quickly andefficiently in a way transparent to the user and the application.

Security

The secured communication in ad hoc wireless network is very important, especially inmilitary applications.

The lack of central coordination and shared wireless medium makes them morevulnerable to attacks than in wired network.

The attacks are generally classified into two types: passive attack and active attacks. Passive attacks refer to attempts made by malicious nodes to perceive the nature of

activities and to obtain information transacted in the network without disrupting the

operation. Active attacks disrupt the operations of the network.

Those active attacks that are executed outside the network are called external attacksand those that are performed by nodes belonging to the same network are called

internal attacks. Nodes that perform internal attacks are compromised nodes.

The major security threats that exist in ad hoc wireless networks are as follows: Denial of service

The attack affected by making the network resource unavailable forservice to other nodes, either by consuming the bandwidth or by

overloading the system, is called denial of service. Eg: by keeping the target node busy by making it process unnecessary

packets.

Resource Consumption The scarce availability of resources makes it easy target for internal

attacks, particularly aiming at resources available in the network.

The major types of resource consumption attacks are the following: Energy depletion: This type of attack is basically aimed at

depleting the battery power of critical nodes by directing the

unnecessary traffic through them.

Buffer overflow: This is carried out either by filling the routingtable with unwanted routing entries or by consuming the data

packet buffer space with unwanted data. Such attacks can lead to

a large number of data packets being dropped, leading to loss of

critical information.

Host impersonation


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A compromised internal node can act as another node and respond withappropriate control packets to create wrong route entries, and can

terminate the traffic meant for the intended destination node.

Information disclosure A compromised node can act as an informer by deliberate disclosure of

confidential information to unauthorized nodes. Information such as the amount and the periodicity of traffic between

selected pair of nodes and pattern of traffic changes can be very

vulnerable for military applications.

Interference A common attack is to jam the wireless communication by creating a

wide spectrum noise. This can be done by using a single wide band

jammer, sweeping across the spectrum.

Addressing and Service Discovery

An address that is globally unique in the connected part of ad hoc network is requiredfor the node in order to participate in communication. Auto configuration of addresses

is required to allocate non duplicate addresses to the nodes.

In network where the topology is highly dynamic, frequent partitioning and merging ofnetwork components require duplicate address detection mechanism in order to

maintain unique addressing throughout the connected parts of the network.

Nodes in the network should be able to locate services that other nodes provide. Henceefficient service advertisement mechanisms are necessary.

Fixed positioning of a server providing a particular service is ruled out. Rather,identifying the current location of the service provider gathers the importance.

The integration of service discovery with the route acquisition mechanism is a viablealternative.Energy Management

Energy management is defined as the process of managing the sources and consumersof energy in a node or in the network as a whole for enhancing the lifetime of the

network.

Energy management can be classified into the following categories: Transmission power management

The power consumed by the radio frequency (RF) module of a mobilenode is determined by several factors such as the state of operation, thetransmission power and the technology used for the RF circuitry.

The state of operation refers to transmit, receive and sleep modes of theoperation.

The transmission power is determined by the reachability requirement ofthe network, the routing protocol and the MAC protocol employed.


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The RF hardware design should ensure minimum power consumption inall the three states of operation. Going to sleep mode when not

transmitting or receiving can be done by additional hardware that wakes

up on reception of control signal.

Power conservation responsibility lies across the data link, network,transport, and application layer. By designing a data link layer protocolthat reduces unnecessary transmission, by preventing collisions, by

switching to standby mode or sleep mode whenever possible, and by

reducing the transmit/receive switching, power management can be

performed at the data link layer.

The network layer routing protocol can consider battery life and relayingload of the intermediate nodes while selecting a path so that the load can

be balanced across the network, in addition to optimizing and reducing

the size and frequency of control packets.

At transport layer, reducing the number of retransmissions, andrecognizing and handling the reason behind the packet losses locally, can

be incorporated into the protocols.

At application layer, the power consumption varies with applications.Application software developed for mobile computers should take into

account the aspect of power consumption as well.

Battery energy management The battery management is aimed at extending the battery life of a node

by taking advantage of its chemical properties, discharge pattern, and by

selection of battery from a set of batteries that is available for

redundancy.

Controlling the charging and discharging rate of the battery is importantin avoiding early charging to the maximum charge or full discharge belowthe minimum threshold. This can be achieved by means of embedded

charge controller in the battery pack.

Protocols at the data link and network layers can be designed to makeuse of discharge model.

Monitoring of the battery for voltage levels, remaining capacity, andtemperature so that proactive actions can be taken.

Processor power management The CPU can be put into different power saving modes during low

processing load conditions. The CPU power can be completely turned off

if the machine is idle for a long time. Interrupts can be used to turn on the CPU upon detection of user

interaction or other events.

Devices power management Intelligent device management can reduce power consumption of mobile

node significantly.


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This can be done by OS by selectively powering down interface devicesthat are not used or by putting devices into different power saving modes

depending on their usage.

Scalability

Commercial deployment of ad hoc wireless network that include wireless mesh networkshow early trends for a widespread installation of ad hoc wireless networks for

mainstream wireless communication.

For example, the latency of path finding involved with an on demand routing protocolin a large ad hoc wireless network may be unacceptably high. Similarly, the periodic

routing overhead involved in table driven routing protocol may consume a significant

amount of bandwidth in such large network.

A large ad hoc wireless network cannot be expected to be formed by homogenousnodes, raising issues such as widely varying resource capabilities across the nodes.

A hierarchical topology based system and addressing may be more suitable for largead hoc wireless network. Hybrid architecture that combines multi hop radio relaying

may improve the scalability.

Deployment Considerations

The deployment of ad hoc wireless networks requires a good amount of planning andestimation of future traffic growth over any link in the network.

The deployment of a commercial ad hoc wireless network has the following benefitswhen compared to wired networks:

Low cost of deployment The use of multi hop wireless relaying essentially eliminates the

requirement of laying cables and maintenance in a commercial

deployment of communication infrastructure.

Incremental deployment In commercial wireless WANs based on ad hoc networks, deployment can

be performed incrementally over geographical regions of the city.

The deployed part starts functioning immediately after the minimumconfiguration is done. Short deployment time

The deployment time is considerably less in ad hoc networks, due toabsence of any wired links.

Reconfigurability The cost involved in reconfiguring wired network coverage a MAN is very

high compared to that of ad hoc network covering the same service area.


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The incremental deployment of ad hoc wireless network might demandchanges in the topology of the fixed part of network at a later stage.

The following are the major issues to be considered in deploying an ad hoc wirelessnetwork:

Scenario of deployment The scenario of deployment assumes significance because the capability

required for a mobile node varies with the environment in which it is

used.

The following are the some of the different scenarios in whichdeployment issues vary widely.

Military deploymento The military deployment may be data centric. The data

centric networks handle a different pattern of data traffic

and can partially comprised of static nodes.

o The vehicle mounted nodes have their disposal betterpower sources and computational resources, where as

hand held devices are constrained by energy and

computational resources. Thus, the resource availability

demands appropriate changes in protocol employed.

o The military application demands for securedcommunication. Routing should involve as few nodes as

possible to avoid possible leakage of information.

o Flat addressing scheme is preferred to hierarchicaladdressing.

Emergency operations deploymento The application scenario demands a quick deployment of

rescue personal equipped with hand heldcommunication equipment.

o The network should provide support of time sensitivetraffic such as voice and video.

o Short data messaging can be used in case the resourceconstraints do not permit voice communication.

o A flat addressing scheme with a static configuration ispreferred.

o The size of the network is not more than 100 nodes. Commercial wide area deployment

oThe aim of the deployment is to provide an alternatecommunication infrastructure for wireless

communications in urban areas and areas where

traditional cellular base stations cannot handle the traffic

volume.

o It provides very low cost per bit transferred compared towide area cellular network infrastructure.


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o Another major advantage is the resilience to failure ofcertain number of nodes.

o Addressing, configuration, positioning of relaying nodes,redundancy of nodes, and power sources are the major

issues in deployment.

o Billing, provisioning of QoS, security and handling mobilityare major issues that the service providers need to

address.

Home network deploymento This deployment need to consider the limited range of the

devices that are to be connected by the network.

o Given the short transmission ranges, it is essential to avoidnetwork partitions.

o Network topology should be decided so that every node isconnected through multiple neighbours for availability.

Required longevity of network The deployment of the network should also consider the required

longevity of the network.

If the network is required for a short while, battery powered mobilenodes may be used. When the connectivity is required for a long duration

of time, fixed radio relaying equipment with regenerative power sources

can be deployed.

A wireless mesh network requires weather proof packages so that theinternal circuitry remains unaffected by environmental conditions.

Area of coverage The area of coverage is determined by the nature of application for which

the network is set up. For example, the home area network is limited to the surrounding of the

home.

In some cases where some nodes can be fixed and the network topologyis partially or fully fixed, the coverage can be enhanced by usage of

directional antennas.

Service availability The availability of network service is defined as the ability of the ad hoc

network to provide service even with failure of certain nodes.

Availability assumes significance both in fully mobile ad hoc network andpartially mobile networks like wireless mesh networks.

Operational integration with other infrastructure Operational integration with other infrastructure can be considered for

improving the performance or gathering additional information or for

providing better QoS.

In military environment, integration of ad hoc wireless networks withsatellite networks or unmanned aerial vehicle (UAVs) improves the

capability to ad hoc wireless networks.


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Some of the routing protocols assume the availability of globalpositioning system (GPS), which is a satellite based infrastructure by

which geographical information can be obtained.

Choice of Protocols The choice of protocols at different layers is to be done taking into

consideration deployment scenarios. A TDMA based and insecure MAC protocol may not be best suited

compared to a CDMA based MAC protocol for a military application.

At network layer, the routing protocol has to be selected with care. Arouting protocol that uses GPS information may not work well in

situations where such information is not available.

An ad hoc wireless network with nodes that cannot have their powersources replenished should use a routing protocol that does not employ

periodic beacons for routing.

At the transport layer, the connection oriented or connectionlessprotocol should be adapted to work in an environment in which the ad

hoc wireless network is deployed.

In a high mobility environment, path breaks, network partitions, andremerging of partitions are to be considered, and appropriate actions

should be taken at the higher layers.

The packet loss arising out if congestion, channel error, link break, andnetwork partition is to be handled differently in different applications.

The timer values at different layers of the protocol stack should beadapted to the deployment scenarios.

Ad Hoc Wireless Internet

The ad hoc wireless internet extends the services of the internet to the end users overan ad hoc wireless network.

Some of the applications of ad hoc wireless internet are wireless mesh networks,provisioning of temporary internet service to major conference venues, sport venues,

temporary military settlements, battlefields, and broadband internet services in rural

regions.


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The major issues to be considered for a successful ad hoc wireless internet are asfollows:

Gateways Gateway nodes are the entry point to the wired internet. The major partof the service provisioning lies with the gateway nodes.

Gateways perform the following tasks: keeping track of end users bandwidth management load balancing traffic shaping packet filtering bandwidth fairness address, service and location discovery

Address mobility The ad hoc wireless internet faces the challenge of address mobility. This

problem is worse here as the nodes operate over multiple wireless hops.

Solution such as mobile IPs can provide temporary alternative for this. Routing

Routing is a problem, due to the dynamic topological changes, thepresence of gateways, multi hop relaying, and the hybrid character of the

network.

Transport layer protocol Split approaches that use traditional wired TCP for the wired part and a

specialized transport layer protocol for the ad hoc wireless network partcan be considered where the gateways act as the intermediate nodes at

which connections are split.

Load balancing The ad hoc wireless internet gateways experience heavy traffic. Hence

the gateway can be saturated much earlier than other nodes in the

network.


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Load balancing techniques are essential to distribute the load so as toavoid the situation where the gateway nodes become the bottle neck.

Pricing/billing It is very important to introduce pricing/billing strategies for the ad hoc

wireless internet.

Gateway is preferred choice for charging the traffic to and from theinternet.

A much more complex case is pricing the local traffic, where it becomesnecessary to have a dedicated, secure, and lightweight pricing/billing

infrastructure installed at every node

Provisioning of security Security is the prime concern in the ad hoc wireless internet. Since the

end users can utilize the ad hoc wireless internet infrastructure to make

the e commerce transactions, it is important to include security

mechanisms in the ad hoc wireless internet.

QoS support With the widespread use of VoIP and growing multimedia applications

over the internet, provisioning of QoS support in the ad hoc wireless

internet becomes a very important issue.

Service, address and location discovery Service discovery refers to the activity of discovering or identifying the

party which provides a particular service or resource.

Address discovery refers to the services such as those provided byaddress resolution protocol (ARP) or domain name service (DNS)

operating within the wireless domain.

Location discovery refers to different activities such as detecting thelocation of a particular node in the network or detecting the geographicallocation of nodes. Location discovery services can provide enhanced

services such as routing of packets, location based services, and

selective region wide broadcast.

adhoc chapter 1

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