Chapter 5 Ad Hoc Wireless

Network

Jang Ping Sheu

Introduction

• Ad Hoc Network is a multi-hop relaying

network

• ALOHAnet developed in 1970

• Ethernet developed in 1980• Ethernet developed in 1980

• In 1994, Bluetooth proposed by Ericsson to

develop a short-range, low-power, low-

complexity, and inexpensive radio inteface

• WLAN 802.11 spec. is proposed in 1997

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Cellular and Ad Hoc Wireless Networks

• Cellular Wireless Networks: infrastructure dependent network

• Ad Hoc Networks: multi-hop radio relaying and without support of infrastructureand without support of infrastructure

– Wireless Mesh Networks

– Wireless Sensor Networks

• The major differences between cellular networks and ad hoc networks as summarized in Table 5.1

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Cellular Wireless Networks Hybrid Wireless

Networks

Wireless Mesh

Networks

Wireless SensorWireless Sensor

Networks

Infrastructure Dependent

(Single-Hop Wireless Networks)

Ad Hoc Wireless Networks

(Multi-Hop Wireless Networks)

Figure 5.1. Cellular and ad hoc wireless networks.

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BB

A

C

DE

Switching Center

+

Gateway

E

Base Station Mobile Node Path from C to E

Figure 5.2. A cellular networks.

Mobile Node

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BB

A

CF

DE

Mobile Node Wireless Link Path from C to E

Figure 5.3. An ad hoc wireless networks2009/11/2 6

Table 5.1 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 routingCentralized routing Distributed routing

Circuit-switched

(evolving toward packet switching)

Packet-switched

(evolving toward emulation of circuit

switching)

Seamless connectivity

(low call drops during handoffs)

Frequency path break

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

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Easier to achieve time synchronization Time synchronization is difficult and

consumes bandwidth

Easier to employ bandwidth reservation Bandwidth reservation requires complex

medium access control protocols

Application domains include mainly civilian

and commercial sector

Application domains include battlefields,

emergency search and rescue operation, and

collaborative computing

High cost of network maintenance

(backup power source, staffing, etc.)

Self-organization and maintenance properties

are built into the network

Table 5.1 Differences between cellular networks and ad hoc

wireless networks (cont.)

(backup power source, staffing, etc.) 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 capacity)

Major goals of routing and call admission are

to maximize the call acceptance ratio and

minimize the call drop ratio

Man 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

Several issues are to be addressed for

successful commercial deployment even

though widespread use exists in defense

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Applications of Ad Hoc Wireless Networks

• Military Applications

– Establishing communication among a group of soldiers for

tactical operations

– Coordination of military object moving at high speeds

such as fleets of airplanes or ships

– Requirements: reliability, efficiency, secure communication, – Requirements: reliability, efficiency, secure communication,

and multicasting routing,

• Collaborative and Distributed Computing

– Conference, distributed files sharing

• Emergency Operations

– Search, rescue, crowd control, and commando operations

– Support real-time and fault-tolerant communication paths92009/11/2

Wireless Mesh Networks

• An alternate communication infrastructure for

mobile or fixed nodes/users

• Provides many alternate paths for a data

transfer session between a source and transfer session between a source and

destination

• Advantages of Wireless Mesh Networks

– High data rate, quick and low cost of deployment,

enhanced services, high scalability, easy

extendability, high availability, and low cost per bit

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Wired Network

Gateway node

A house with rooftop transceiver

Transmission range

Wired link to the Internet

Wireless link

Figure 5.4. Wireless mesh networks operating in a residential zone

Gateway node

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Internet

Wired link to the Internet

Multi-hop radio relay link Lamp

Radio relay node

Figure 5.5 Wireless mesh network covering a highway

Coverage area

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Wireless Sensor Networks

• A collection of a large number of sensor nodes

that are deployed in a particular region

• Applications:

– military, health care, home security, and

environmental monitoringenvironmental monitoring

• Differences with the ad hoc wireless networks:

– Mobility of nodes, size of network, density of

deployment, power constraints, data/information

fusion, traffic distribution

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Hybrid Wireless Networks

• HWN such as Multi-hop cellular networks and

integrated cellular ad hoc relay networks

– The base station maintains the information about the

topology of the network for efficient routing

– The capacity of a cellular network can be increased if the

network incorporates the properties of multi-hop relaying network incorporates the properties of multi-hop relaying

along with the support of existing fixed infrastructure

• Advantages:

– Higher capacity than cellular networks due to better

channel reuse

– Increased flexibility and reliability in routing

– Better coverage and connectivity in holes2009/11/2 14

BB

A

C

Switching Center

+

Gateway

D

E

Mobile NodeBase Station MCN communication

Figure 5.6. MCN architecture.

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Issues in Ad Hoc Wireless Networks

• Medium access scheme

• Routing, Multicasting, TPC protocol

• Pricing scheme, QoS, Self-organization

• Security, Energy management• Security, Energy management

• Addressing and service discovery

• Deployment considerations

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Medium Access Scheme

• Distributed operation

– fully distributed involving minimum control overhead

• Synchronization

– Mandatory for TDMA-based systems

• Hidden terminals• Hidden terminals

– Can significantly reduce the throughput of a MAC protocol

• Exposed terminals

– To improve the efficiency of the MAC protocol, the exposed

nodes should be allowed to transmit in a controlled fashion

without causing collision to the on-going data transfer

• Access delay

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The Major Issues of MAC Scheme

• Throughput and access delay

– To minimize the occurrence of collision, maximize channel

utilization, and minimize controloverhead

• Fairness

– Equal share or weighted share of the bandwidth to all

competing nodescompeting nodes

• Real-time traffic support

• Resource reservation

– Such as BW, buffer space, and processing power

• Capability for power control

• Adaptive rate control

• Use of directional antennas

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The Major Challenge of Routing Protocol

• Mobility result in frequent path break, packet

collision, and difficulty in resource reservation

• Bandwidth constraint: BW is shared by every node

• Error-prone and share channel: high bit error rate

• Location-dependent contention: distributing the

network load uniformly across the network

• Other resource constraint: computing power, battery

power, and buffer storage

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The Major Requirement of Routing Protocol

• Minimum route acquisition delay

• Quick route reconfiguration: to handle path breaks

• Loop-free routing

• Distributed routing approach

• Minimum control overhead• Minimum control overhead

• Scalability

• Provisioning of QoS:

• supporting differentiated classes of services

• Support for time-sensitive traffic

• Security and privacy

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The Major Issues in Multicast Routing

Protocols

• Robustness

– recover and reconfigure quickly from link breaks

• Efficiency

– minimum number of transmissions to deliver a data packet

to all the group membersto all the group members

• Minimal Control overhead

• QoS support

• Efficient group management

• Scalability

• Security

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Transport Layer Protocols

• Objectives: setting up and maintaining

– End-to-end connections, reliable end-to-end data

delivery, flow control, and congestion control

• Major performance degradation:• Major performance degradation:

– Frequent path breaks, presence of old routing

information, high channel error rate, and frequent

network partitions

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Quality of Service Provisioning

• QoS often requires negotiation between the host and

the network, resource reservation schemes, priority

scheduling and call admission control

• QoS in Ad hoc wireless networks can be on a per

flow, per link, or per node

• Qos Parameters: different applications have different

requirements

– Multimedia: bandwidth and delay are the key parameters

– Military: BW, delay, security and reliability

– Emergency search –and-rescue: availability is the key

parameters, multiple link disjoint paths

– WSN: battery life, minimum energy consumption2009/11/2 23

Quality of Service Provisioning

• QoS-aware routing:

– To have the routing use QoS parameters for finding a path

– The parameters are network through put, packet delivery

ratio, reliability, delay, delay jitter, packet lost rate, bit error

rate, and path loss

• QoS framework:

– A frame work for QoS is a complete system that attempts

to provide the promised service

– The QoS modules such as routing protocol, signaling

protocol, and resource management should react

promptly according to changes in the network state

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Self-Organization

• An important property that an ad hoc wireless

network should exhibit is organizing and maintaining

the network by itself

• Major activities: neighbor discovery, topology

organization, and topology reorganizationorganization, and topology reorganization

• Ad hoc wireless networks should be able to perform

self-organization quickly and efficiently

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Security

• The attack against ad hoc wireless networks are

classified into two types: passive and active attacks

• Passive attack: malicious nodes to observe the

nature of activities and to obtain information in the

network without disrupting the operationnetwork without disrupting the operation

• Active attack: disrupt the operation of the network

– Internal attack: nodes belong to the same network

– External attack: nodes outside the network

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Major Security Threats

• Denial of service: either consume the network BW or overloading the system

• Resource consumption

– Energy depletion: by directing unnecessary traffic through nodes

– Buffer overflow: filling unwanted data, routing table attack – Buffer overflow: filling unwanted data, routing table attack (filling nonexistent destinations)

• Host impersonation: A compromised node can act as another node and respond control packets to create wrong route entries and terminate the traffic

• Information disclosure: support useful traffic pattern

• Interference: create wide-spectrum noise

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Addressing and Service Discovery

• An address that is globally unique is required for a

node to participate communication

– Auto-configuration of address is required to allocate non-

duplicate address to the nodes

– In networks frequent partitioning and merging of network – In networks frequent partitioning and merging of network

components require duplicate address detection

mechanisms

• Nodes in the network should be able to locate

services that other nodes provide

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Energy Management

• Transmission power management:

– RF hardware design ensure minimum power consumption

– Uses variable power MAC protocol

– Load balance in network layer

– Reducing the number of retransmissions at the transport

layer

– Application software developed for mobile computers

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Energy Management (cont.)

• Battery energy management: extending the battery

life by taking chemical properties, discharge patterns,

and by the selection of a battery from a set of

batteries that is available for redundancy

• Processor power management: CPU can be put into • Processor power management: CPU can be put into

different power saving modes during low processing

load conditions

• Devices power management: can be done by OS by

selectively powering down interface devices that are

not used or by putting devices into different power-

saving modes302009/11/2

Scalability

• The latency of path-finding involved with an

on-demand routing protocol in a large ad hoc

wireless network may be unacceptably high

• A hierarchical topology-based system and •addressing may be more suitable for large ad

hoc wireless networks

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Deployment Considerations

• The deployment of a commercial ad hoc wireless

network has the following benefits

– Low cost of deployment

– Incremental deployment

– Short deployment time– Short deployment time

– Re-configurability

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Major Issues for Deployment

• Scenario of deployment

– Military deployment

• Data-centric (e.g. WSN)

• User-centric (soldiers or vehicles carrying with wireless

communication devices)

– Emergency operations deployment

– Commercial wide-area deployment

– Home network deployment

• Required longevity of network: regenerative power

source can be deployed when the connectivityis

required for a longer duration of time

• Area of coverage2009/11/2 33

Major Issues for Deployment

• Service availability: redundant nodes can be

deployed to against nodes failure

• Operational integration with other infrastructure:

can be considered for improve the performance or

gathering additional information, or for providing gathering additional information, or for providing

better QoS

• Choice of protocols: the choices of protocols at

different layers of the protocol stack is to be done

taking into consideration the deployment scenario

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Ad Hoc Wireless in Internet

• Similar to wireless internet, the ad hoc

wireless internet extends the service of the

Internet to the end user over an ad hoc

wireless network

• Gateways: entry points to the wired Internet• Gateways: entry points to the wired Internet

• Address mobility: similar to the Mobile IP

• Routing: major problem in ad hoc wireless Internet

• Transport layer protocol

• Load balancing, pricing/billing, security, QoS

• Service, address, and location discovery

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Application Layer

(HTTP, TELNET, SMTP,

etc.)

Transport Layer

(TCP/UDP)

Network Layer

(IPv4/IPv6)

802.11/HIPERLAN

Network Layer

(IPv4/IPv6)

802.11

HIPERLAN

802.3/802.4/80

2.5

Application Layer

(HTTP, TELNET, SMTP,

etc.)

Transport Layer

(TCP/UDP)

Network Layer

(IPv4/IPv6)

802.11/HIPERLAN

Application Layer

(HTTP, TELNET, SMTP,

etc.)

Transport Layer

(TCP/UDP)

Network Layer

(IPv4/IPv6)

802.3/802.4/802.5

TCP/IP protocol stack TCP/IP protocol stack TCP/IP protocol stack

InternetAd hoc wireless Internet gateway connected to a subnet of the Internet

Mobile node that can relay packets to any mobile node running ad hoc wireless routing protocol

Multi-hop wireless part of ad hoc wireless Internet Traditional wired Internet

Flow of an IP packet from the wired Internet to a mobile node

Transceiver antenna

Mobile node that can be connected to any AP running ad hoc wireless routing protocol

Figure 5.7. A schematic diagram of the ad hoc wireless Internet2009/11/2 36

Internet

Gateway Node

A

A house with rooftop transceiver Transmission range

Wired link to the Internet

Wireless link

Figure 5.8. An illustration of the ad hoc wireless Internet implemented

by a wireless mesh network

Path 1

Path 2

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Home Work

• 4, 8, 11, 13

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