Lecture 5 6 .ad hoc network

Chandra Prakash

Assistant Professor

LPU

Ad Hoc Network

Lecture (5-6)

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Introduction

Introduction - Ad Hoc Network definition

Characteristic/features and application

Heterogeneity in Mobile Devices

Wireless Sensor Networks

Traffic Profiles

Types of Ad Hoc Mobile Communications

Types of Mobile Host Movements

Challenges Facing Ad Hoc Mobile Networks

Issues and Challenges Facing Ad Hoc Mobile network

Ad Hoc wireless Internet

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A BSS without an AP is called an ad hoc network;

a BSS with an AP is called an infrastructure network.

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Ad hoc networks

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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What Is an Ad Hoc Network?

An ad hoc wireless network

collection of two or more devices equipped with

wireless communications and networking capability.

Such devices can communicate with another node that is

immediately within their radio range or one that is outside

their radio range.

For the latter scenario, an intermediate node is used to relay or

forward the packet from the source toward the destination.

Since an ad hoc wireless network does not rely on any fixed

network entities, the network itself is essentially infrastructure-

less. There is no need for any fixed radio base stations, no wires or

fixed routers.

5

(cont…)

An ad hoc wireless network is self-organizing and adaptive.

This means that a formed network can be de-formed on-the-

fly without the need for any system administration.

The term "ad hoc" tends to imply "can take different

forms" and "can be mobile, standalone, or

networked.“

Ad hoc nodes or devices should be able to detect the

presence of other such devices and to perform the necessary

handshaking to allow communications and the sharing of

information and services.

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Wireless Ad-hoc Network A wireless ad-hoc network is a decentralized type

of wireless network.

The network is ad hoc because it does not rely on a pre-existing infrastructure, such as routers in wired networksor access points in managed (infrastructure) wirelessnetworks.

Each node participates in routing by forwarding data for othernodes, and so the determination of which nodes forward datais made dynamically based on the network connectivity.

In addition to the classic routing, ad hoc networks canuse flooding for forwarding the data.

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Mobile Ad Hoc Networks (MANET)

Mobile nodes

Access points

Backbone

Wireless Mobile Network

MANET

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Mobile Ad-hoc Network

Self-configuring network of mobile routers (and associatedhosts) connected by wireless links

This union forms a random topology

Routers move randomly free

Topology changes rapidly and unpredictably

Standalone fashion or connected to the larger Internet

While MANETs are self contained, they can also be tied to anIP-based global or local network – Hybrid MANETs

Suitable for emergency situations like natural or human-induceddisasters, military conflicts, emergency medical situations, etc.

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Cellular and ad hoc wireless networks

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Comparison of wireless cellular and wireless ad-hoc network

concepts

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MANET ApplicationApplications Descriptions/Services

Tactical Networks •Military communication, operations

•Coordination of military object moving at high speeds such as fleets

of airplanes or ships

•Automated battlefields

Sensor networks •Collection of embedded sensor devices used to collect real time data

to automate everyday functions. Data highly correlated in time and

space, e.g., remote sensors for weather, earth activities; sensors for

manufacturing equipments.

•Can have between 1000 -100,000 nodes, each node collecting sample

data, then forwarding data to centralized host for processing using low

homogeneous rates.

Emergency

services

•Search, rescue, crowd control, and commando operations as well as

disaster recovery

•for e.g. Early retrieval and transmission of patient data ( record,

status, diagnosis ) from /to the hospital

•Replacement of a fixed infrastructure in case of earthquakes,

hurricanes, fire etc.12

MANET ApplicationApplications Descriptions/Services

Commercial

environments

•E-commerce, e.g., electronic payments from anywhere (i.e., in taxi).

•Business:

dynamic access to customer files stored in a central location

on the fly provide consistent databases for all agents

Mobile office

•Vehicular services:

transmission of news ,road conditions ,weather, music

local ad hoc network with nearby vehicles for road/accident

guidance

Home and

enterprise

networking

•Home/office wireless networking(WLAN), e.g., shared whiteboard

application, use PDA to print anywhere, trade shows

•Personal area network (PAN)

Educational

applications

•Set up virtual classrooms or conference rooms

•Set up ad hoc communication during conferences, meetings, or

lectures13

MANET Application

Applications Descriptions/Services

Entertainment Multiuser games

Robotic pets

outdoor internet access

Location- aware

Services

Follow- on services, e.g., automatic call forwarding, transmission of the

actual workspace to the current location

Information services

push, e.g., advertise location-specific services, like gas stations

pull, e.g., location-dependent travel guide; services( printer, fax,

phone, server, gas stations) availability information; caches,

intermediate results, state information, etc.

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Issues in Ad-Hoc Ad hoc wireless devices can take different forms (for example,

palmtop, laptop, Internet mobile phone, etc.), the computation,

storage, and communications capabilities and

interoperability of such devices will vary tremendously.

Ad hoc devices should not only detect the presence of connectivity

with neighbouring devices/nodes, but also identify what type the

devices are and their corresponding attributes.

Due to the presence of mobility, routing information will have to

change to reflect changes in link connectivity.

The diversity of ad hoc mobile devices also implies that the battery

capacity of such devices will also vary. Since ad hoc networks rely on

forwarding data packets sent by other nodes, power consumption

becomes a critical issue.15

Heterogeneity in Mobile Devices

(a) Heterogeneous mobile device ad hoc networks, and (b) homogeneous ad hoc

network comprising powerful laptop computers.16

Heterogeneity in Mobile Devices

The presence of heterogeneity implies that some devices are

more powerful than others, and some can be servers while

others can only be clients.

It is evident that there are differences in size, computational

power, memory, disk, and battery capacity.

Mobile devices can exist in many forms. There are great

differences among these devices,

heterogeneity can affect communication performance and

the design of communication protocols.

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Characteristics of some existing

mobile devices

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Heterogeneity in Mobile Devices

Come in different favours:

Sensor Network

Personal Area Network

Traditional Mobile Ad Hoc Network

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WIRELESS SENSOR NETWORK

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INTRODUCTION TO WSN A wireless sensor network is one form of an ad hoc wireless

network.

A sensor network is a collection of a large number of

sensor nodes that are deployed in a particular region.

Sensors are wirelessly connected and they, at appropriate times, relay

information back to some selected nodes.

These selected nodes then perform some computation based on the

collected data to derive an ultimate statistic to allow critical

decisions to be made.

There are a variety of sensors, including acoustic(sound related) ,

seismic (Subject to an earthquake or earth vibration), image, heat,

direction, smoke, and temperature sensors.

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Basic features of sensor networks

A large number of low-cost, low-power, multifunctional, and small sensor

nodes

Sensor node consists of sensing, data processing, and communicating

components

A sensor network is composed of a large number of sensor nodes,

which are densely deployed either inside the phenomenon or very close

to it.

The position of sensor nodes need not be engineered or pre-determined.

sensor network protocols and algorithms must possess self-organizing

capabilities.

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Basic features of sensor networks

Self-organizing capabilities

Short-range broadcast communication and multihop routing

Dense deployment and cooperative effort of sensor nodes

Frequently changing topology due to fading and node

failures

Limitations in energy, transmit power, memory, and computing

power

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Wireless 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

No 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)

Mobility of nodes is not mendatory

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 Net

Wireless

Sensor

Network

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Existing Wireless Net vs. Sensor NetCellular system Bluetooth, MANET Sensor Network

Single Hop Multi-hop Multi-hop

High QOS

Bandwidth efficiency

High QOS Power conservation

Limited bandwidth

Large number of node

Narrow radio range

Frequent topology change

Station to Base station Peer to peer

Peer to multi node

Peer to multi node

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Factors influencing sensor network design

Fault tolerance;

Scalability;

Production costs;

Operating environment;

Sensor network topology;

Hardware constraints;

Transmission media;

Power consumption.

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Sensor Network Model

SourceStimulus

Sink

Sink

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Sensor 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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Components of Sensor Node

A sensor node is made up of four basic components sensing unit usually composed of two subunits: sensors and analog to digital converters

(ADCs).

processing unit, Manages the procedures that make the sensor node collaborate with the other

nodes to carry out the assigned sensing tasks.

Transceiver unit Connects the node to the network.

Power units (the most important unit)

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Sensor network topology

Pre-deployment and deployment phase

Sensor nodes can be either thrown in mass or placed one by one in the sensor field.

Post-deployment phase

Sensor network topologies are prone to frequent changes after deployment.

Re-deployment of additional nodes phase

Addition of new nodes poses a need to re-organize the network.

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DEPLOYMENT OF NODES IN WSN

DeploySensors

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Environment

Sensor nodes may be working in busy intersections, in the interior of a large machinery, at the bottom of an ocean, inside a twister, in a battlefield beyond the enemy lines, in a home or a large building

Transmission media Industrial, scientific and medical (ISM) bands offer license-free communication in most countries.

Infrared License-free and robust to interference requirement of a line of sight between sender and receiver

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Micro-sensors

Uses

In military: surveillance and target tracing

health-care industry: allow continuous monitoring of life-

critical information.

food industry: biosensor technology applied to quality control

can help prevent rejected products from being shipped out,

Agriculture: help to determine the quality of soil and moisture

level; they can also detect other bio-related compounds.

Sensors are also widely used for environmental and weather

information gathering. They enable us to make preparations in

times of bad weather and natural disaster.

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APPLICATIONS OF WSN

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Wireless Mesh Networks

Mesh networking is the holy grail of wireless networking.

“Mesh” refers to many types of technology that enable

wireless systems to automatically find each other and self-

configure themselves to route information amongst

themselves.

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Wireless Mesh Networks Mesh network implemented over

WLAN

“Mesh” refers to many types of

technology that enable wireless

systems to automatically find each

other and self-configure themselves to

route information amongst themselves.

Industrial standards Activities

IEEE 802.11, IEEE 802.15, IEEE

801.16 have established sub-working

groups to focus on new standards for

WMNs

In a wireless mesh network, the network connection is spread out among

dozens or even hundreds of wireless mesh nodes that "talk" to each other

to share the network connection across a large area.

Mesh nodes are small radio transmitters that function in the same way as a

wireless router.

In a wireless mesh network, only one node needs to be physically

wired to a network connection like a DSL Internet modem. That

one wired node then shares its Internet connection wirelessly with all other

nodes in its vicinity. Those nodes then share the connection wirelessly with

the nodes closest to them. The more nodes, the further the connection

spreads, creating a wireless "cloud of connectivity" that can serve a small

office or a city of millions.

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Wireless Mesh Networks Possible deployment scenarios:

Residential zone : where broadband connectivity is required

Highway: where a communication facility for moving automobiles

is required

Business zones: where an alternative communication system to

cellular network is required

Important civilian regions: where a high degree of service

availability is required

University campus: where inexpensive campus wide network

coverage can be provided.

Operates at license-free ISM band -2.4 GHz and 5 GHz.

Speed - 2Mbps to 60 Mbps 38

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Benefits Using fewer wires means it costs less to set up a network, particularly for large areas of coverage.

The more nodes you install, the bigger and faster your wireless network becomes.

They rely on the same WiFi standards (802.11a, b and g) already in place for most wireless

networks.

They are convenient where Ethernet wall connections are lacking -- for instance, in

outdoor concert venues, warehouses or transportation settings.

They are useful for Non-Line-of-Sight (NLoS) network configurations where wireless

signals are intermittently blocked. For example, in an amusement park a Ferris wheel occasionally

blocks the signal from a wireless access point.

Wireless mesh configurations allow local networks to run faster, because local packets don't

have to travel back to a central server.

Wireless mesh nodes are easy to install and uninstall, making the network extremely adaptable and

expandable as more or less coverage is needed.

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Electric meters now being deployed on residences transfer their readings from

one to another and eventually to the central office for billing without the need

for human meter readers or the need to connect the meters with cables.

Mesh networks are "self configuring;" the network automatically incorporates a

new node into the existing structure without needing any adjustments by a

network administrator.

Mesh networks are "self healing," since the network automatically finds the

fastest and most reliable paths to send data, even if nodes are blocked or lose

their signal.

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TaxonomyWireless

Networking

Multi-hop

Infrastructure-less

(ad-hoc)

Infrastructure-based

(Hybrid)Infrastructure-less

(MANET)

Single

Hop

Cellular

Networks Wireless Sensor

NetworksWireless Mesh

Networks

Car-to-car

Networks

(VANETs)

Infrastructure-based

(hub&spoke)

802.11 802.16 Bluetooth802.11

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Mesh vs. Ad-Hoc Networks

Multihop

Nodes are wireless, possibly mobile

May rely on infrastructure

Most traffic is user-to-user

Ad-Hoc Networks Wireless Mesh Networks

Multihop

Nodes are wireless,

some mobile, some

fixed

It relies on

infrastructure

Most traffic is user-

to-gateway

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Mesh vs. Sensor Networks

Bandwidth is limited (tens of kbps)

In most applications, fixed nodes

Energy efficiency is an issue

Resource constrained

Most traffic is user-to-gateway

Wireless Sensor Networks Wireless Mesh Networks

Bandwidth is generous (>1Mbps)

Some nodes mobile, some fixed

Normally not energy limited

Resources are not an issue

Most traffic is user-to-gateway

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Broadband Internet Access

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Extend WLAN Coverage

Source: www.belair.com

Source: www.meshdynamics.com

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WMN 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 WMNs

Internet

Wi-Fi

Networks

Cellular

Networks WiMAX

Networks

Sensor

NetworksBase Station

Sink nodeSensor

Wireless Mesh

Backbone

Wired ClientsMesh RouterMesh Router

with Gateway

Mesh Router

with Gateway

Mesh Router

with Gateway/Bridge

Mesh Router

with Gateway/Bridge

Mesh Router

with Gateway/Bridge

Access Point

Base Station

Mesh Router

with Gateway/Bridge

Wireless Clients

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Client WMNs

Mesh Client

Mesh Client

Mesh Client

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Hybrid WMNs

Wi-Fi, Wi-MAX,

Sensor Networks,

Cellular Networks, etc.

Internet

Wireless Mesh Clients

Wireless Mesh

Backbone

Conventional Clients

Mesh Router

Mesh Router

Mesh Router

with Gateway

Mesh Router

with Gateway

Mesh Router

with Gateway/Bridge

Mesh Router Mesh Router

Mesh Router

with Gateway/Bridge

Types of Ad Hoc Mobile

Communications

Mobile hosts in an ad hoc mobile network can communicate

with their immediate peers (peer-to-peer) that are a single

radio hop away.

If three or more nodes are within range of each other (but

not necessarily a single hop away from one another), then

remote-to-remote mobile node communications

exist.

Remote-to-remote communications are associated with

group migrations.

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Types of traffic patterns in Adhoc

Ad hoc wireless communications can occur in several different

forms.

1) Peer-to-peer communication

Mobile host communicates in pair

For a pair of ad hoc wireless nodes, communications will occur

between them over a period of time until the session is

finished or one of the nodes has moved away.

2) Remote-to-remote communication

when two or more devices are communicating among

themselves and they are migrating in groups.

The traffic pattern is, therefore, one where communications

occur over a longer period of time.52

Types of traffic patterns in Adhoc

3) Hybrid Communication

have a scenario where devices communicate in a non-

coherent fashion and their communication sessions are,

therefore, short, abrupt, and undeterministic.

MH: Mobile host53

Types of Mobile Host Movements

Movements by Nodes in a Route

Movements by Subnet-Bridging Nodes

Concurrent Node Movements

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Movements by Nodes in a Route

Source nodes

Downstream link

Intermediate nodes

Destination nodes

Upstream link

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Cont…An ad hoc route comprises the source (SRC), destination (DEST), and/or a

number of intermediate nodes (INs).

Movement by any of these nodes will affect the validity of the route.

An SRC node

has a downstream link, and

when moves out of its downstream neighbour's radio coverage range, the existing

route will immediately become invalid.

all downstream nodes may have to be informed so they can erase their invalid route

entries.

DEST node

moves out of the radio coverage of its upstream neighbour, the route becomes

invalid.

The upsteam nodes will have to be informed so they can erase their invalid route

entries.

IN node : any movement by an IN supporting an existing route may cause the

route to be invalid.56

Movements cause many conventional distributed routing

protocols to respond in sympathy with the link changes.

Need to update all the remaining nodes within the network

so that consistent routing information can be maintained.

Updating process involves broadcasting over the

wireless medium, which results in wasteful bandwidth and

an increase in overall network control traffic. Hence, new

routing protocols are needed.

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Movements by Subnet-Bridging Nodes Subnet-bridging node movement

between two mobile subnets can

fragment the mobile subnet into

smaller subnets

Movements by certain nodes can

result in subnets merging (yielding

bigger subnets) while sometimes

subnet is partitioned by some subnet-

bridging mobile nodes

Updating all the nodes' routing tables

Choose to update only the affected

nodes' association tables.

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Concurrent movements by nodes (SRC, DEST, or

INs)

Ensure there is consistency when multiple route

reconfiguration or repair processes are invoked.

Ultimately converge where the most appropriate

route reconfiguration is performed.

Concurrent Node Movements

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Challenges 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 Networks1. Spectrum Allocation and Purchase

2. Medium access scheme

3. Routing

4. Multicasting

5. Transport layer protocol Performance

6. Pricing shceme

7. QoS provisioning

8. Security

9. Energy management

10. Addressing and service discovery

11. Scalability

12. Deployment considerations61

1. Spectrum Allocation and Purchase

FCC control the regulations regarding the use of radio

spectrum.

Who regulates the use of radio spectrum in INDIA??

To prevent interference, ad hoc networks operate over

some form of allowed or specified spectrum range.

Most microwave ovens operate in the 2.4GHz band, which

can therefore interfere with wireless LAN systems.

Frequency spectrum is not only tightly controlled and

allocated, but it also needs to be purchased.

With ad hoc networks capable of forming and deforming on-

the-fly, it is not clear who should pay for this spectrum.62

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2.Medium 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

Media Access TDMA and FDMA schemes are not suitable.

Many MAC (Media Access Control) protocols do not deal with host

mobility.

The scheduling of frames for timely transmission to support QoS is difficult.

In ad hoc wireless networks, since the same media are shared by multiple

mobile ad hoc nodes, access to the common channel must be made in a

distributed fashion, through the presence of a MAC protocol.

There are no static nodes, nodes cannot rely on a centralized coordinator.

The MAC protocol must contend for access to the channel while at the same

time avoiding possible collisions with neighboring nodes.

The presence of mobility, hidden terminals, and exposed nodes

problems must be accounted for when it comes to designing MAC

protocols for ad hoc wireless networks.

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Difference Between Wired and

Wireless

If both A and C sense the channel to be idle at the same time, they send at the same time.

Collision can be detected at sender in Ethernet.

Half-duplex radios in wireless cannot detect collision at sender.

A B C

A

B

C

Ethernet LAN Wireless LAN

IEEE has defined the specifications for a wireless LAN, called IEEE 802.11, which covers the physical and data link layers.

In IEEE 802.11, carrier sensing is performed at the air interface (physical carrier sensing), andat the MAC layer (virtual carrier sensing)

Physical carrier sensingdetects presence of other users by analyzing all detected packets Detects activity in the channel via relative signal strength from other sources

Virtual carrier sensing is done by sending MPDU duration information in the header of RTS/CTS and data framesChannel is busy if either mechanisms indicate it to beDuration field indicates the amount of time (in microseconds) required to complete frame transmissionStations in the BSS use the information in the duration field to adjust their network allocation vector (NAV)

802.11 - Carrier Sensing

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A and C cannot hear each other.

A sends to B, C cannot receive A.

C wants to send to B, C senses a “free” medium.

Collision occurs at B.

A cannot receive the collision.

A is “hidden” for C.

Hidden Terminal Problem

BA C

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Exposed Terminal Problem

A starts sending to B.

C senses carrier, finds medium in

use and has to wait for A->B to

end.

D is outside the range of A,

therefore waiting is not necessary.

A and C are “exposed” terminals

A B

CD

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3. Routing

Challenges

Mobility

results in path breaks, packet collisions, transient loops, stale routing

information, and difficulty in resource reservation

BW constraints

Error-prone and shred channel

Bit error rate BER: 10-5 ~ 10-3 wireless vs. 10-12 ~ 10-9 wired

Location-dependent contention

Distribute load uniformly

Routing The presence of mobility implies that links make and break often and in an

indeterministic fashion.

Classical distributed Bellman-Ford routing algorithm is used to

maintain and update routing information in a packet radio network.

Yet distance-vector-based routing not designed for wireless networks,

still applicable to packet radio networks since the rate of mobility is not

high.

Mobile devices are now small, portable, and highly integrated.

Ad hoc mobile networks are different from packet radio networks since

nodes can move more freely, resulting in a dynamically changing topology.

Existing distance-vector and link-state-based routing protocols

are unable to catch up with such frequent link changes in ad hoc wireless

networks, resulting in poor route convergence and very low

communication throughput. Hence, new routing protocols are needed70

Routing protocolsRouting protocols

Purpose is to dynamically communicate information about all

network paths used to reach a destination and to select the from

those paths, the best path to reach a destination network.

Types of routing protocol

Distance –vector Routing Protocol

Distance vector protocols use a distance calculation (distance metric) plus

an outgoing network interface (a vector) to choose the best path to a

destination network.

The network protocol (IPX, SPX, IP, Appletalk, DECnet etc.) will forward

data using the best paths selected

Well Supported Protocols such as RIP have been around a long time and

most, if not all devices that perform routing will understand RIP.

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Link state based

Selects the best routing path by calculating the state of each link

in a path and finding the path that has the lowest total metric to

reach the destination.

Link State protocols track the status and connection type of

each link and produces a calculated metric based on these and

other factors, including some set by the network administrator.

Link state protocols know whether a link is up or down and

how fast it is and calculates a cost to 'get there'.

Link State protocols will take a path which has more hops, but

that uses a faster medium over a path using a slower medium

with fewer hops.

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Difference If all routers were running a Distance Vector protocol, the path or

'route' chosen would be from A B directly over the ISDN serial link,

even though that link is about 10 times slower than the indirect route

from A C D B.

A Link State protocol would choose the A C D B path because it's

using a faster medium (100 Mb ethernet).

In this example, it would be better to run a Link State routing protocol,

but if all the links in the network are the same speed, then a Distance

Vector protocol is better.

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Routing (2)

Requirements

Minimum route acquisition delay

Quick route reconfiguration

Loop-free routing

Distributed routing approach

Minimum control overhead

Scalability

QoS provisioning

Support for time-sensitive traffic

Security and privacy

4. Multicasting

Multiparty communcations are enabled through the

presence of multicast routing protocols.

The multicast backbone (MBone) comprises an

interconnection of multicast routers that are capable of

tunnelling multicast packets through non-multicast routers.

Some multicast protocols use a broadcast-and-prune

approach to build a multicast tree rooted at the

source.Others use core nodes where the multicast tree

originates.

All such methods rely on the fact that routers are

static, and once the multicast tree is formed, tree nodes will

not move. However, this is not the case in ad hoc wireless

networks.75

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Multicasting

Robusteness

recover and reconfigure quickly from potential mobility-

induced link breaks

Efficiency

Min control overhead

QoS support

Efficient group management

Scalability

security

5. Energy Efficiency Mobile devices today are mostly operated by batteries. Battery

technology is still lagging behind microprocessor technology.

The lifetime of an Li-ion battery today is only 2-3 hours. Such a

limitation in the operating hours of a device implies the need for

power conservation.

For ad hoc mobile networks, mobile devices must perform both the

role of an end system (where the user interacts and where user

applications are executed) and that of an intermediate system

(packet forwarding).

Hence, forwarding packets on the behalf of others will consume

power, and this can be quite significant for nodes in an ad hoc

wireless network.

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Energy Management

Tx power mgmt

MAC: sleep mode

Routing: consider battery life time: load balancing

Transport: reduce ReTx

App

Battery energy mgmt

Extend 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

6. TCP Performance

TCP is an end-to-end protocol designed to provide flow and

congestion control in a network. TCP is a connection-

oriented protocol; hence, there is a connection

establishment phase prior to data transmission. The

connection is removed when data transmission is completed.

TCP (Transmission Control Protocol) assumes that nodes in

the route are static, and only performs flow and

congestion activities at the SRC and DEST nodes.

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TCP relies on measuring the round-trip time (RTT) and packet loss

to conclude if congestion has occurred in the network.

In telecommunications, the round-trip delay time

(RTD) or round-trip time (RTT) is the length of time it takes for

a signal to be sent plus the length of time it takes for an

acknowledgment of that signal to be received. This time delay

therefore consists of the transmission times between the two points of

a signal.

TCP is unable to distinguish the presence of mobility and

network congestion.

Mobility by nodes in a connection can result in packet loss and long

RTT.

Enhancements needed to ensure that the transport protocol performs

properly without affecting the end-to-end communication throughput.80

7. Service Location, Provision, and

Access

Ad hoc networks comprise heterogeneous devices and

machines and not every one is capable of being a server.

The concept of a client initiating task requests to a server for

execution and awaiting results to be returned may not be

attractive due to limitations in bandwidth and power.

Concept of remote programming as used in mobile agents is

more applicable since this can reduce the interactions

exchanged between the client and server over the wireless

media.

Also, how can a mobile device access a remote service in an

ad hoc network? How can a device that is well-equipped

advertise its desire to provide services to the rest of the

members in the network? All these issues demand research.81

8. Security & Privacy

Ad hoc networks are intranets and remain as intranets unless

connected to Internet.

Such confined communications have already isolated

attackers who are not local in the area.

Through neighbor identity authenication, a user can know if

neighboring users are friendly or hostile.

Information sent in an ad hoc route can be protected in some

way but since multiple nodes are involved, the relaying of

packets has to be authenicated by recognizing the originator

of the paket and the flow ID or label.

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Security

DoS attack

Resource consumption

Energy depletion

Buffer overflow

Host impersonation

Information disclosure

Interference

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9. Deployment Consideration (1)

Adv. in ad hoc net

Low cont of deployment

Incremental deplyment

Short deplyment time

Reconfigurablity

Scenario of deployment

Military deployment: data-centric or user-centric

Emergency operation deployment: hend-held, voice/data,

< 100 nodes

Commercial wide-area deployment: e.g. WMN

Home network deplyment

85

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 ?