advanced techniques of mobile ad hoc and wireless sensor networks chapter: 05-mobile computing...

Advanced Techniques of Mobile Ad Hoc and Wireless Sensor Networks

Chapter: 05-Mobile Computing Mobile Adhoc Networks

By: Mr. Abdul Haseeb Khan

https://mail.ntpu.edu.tw/indexi.html


MANETS Definition Ad hoc vs. cellular networks MANETS Applications MANETS Challenges

Routing Protocol Expected Properties of Ad-hoc Routing

Protocols A taxonomy for routing protocols in Mobile ad common protocols(DSDV, AODV, DSR, ZRP,

TORA)

Outline


Typical wireless network: Based on infrastructure E.g., GSM, UMTS, … Base stations connected to a wired backbone network Mobile entities communicate wirelessly to these base stations Traffic between different mobile entities is relayed by base stations and wired backbone Mobility is supported by switching from one base station to another Backbone infrastructure required for administrative tasks

Infrastructure-based wireless networks

IP backbone

ServerRouter

Furth

er

network

s

Gateways


What if … No infrastructure is available? – E.g., in

disaster areas It is too expensive/inconvenient to set up? –

E.g., in remote, large construction sites There is no time to set it up? – E.g., in military

operations

Infrastructure-based wireless networks – Limits?


Possible applications for infrastructure-free networks

Factory floor automation

· Disaster recovery · Car-to-car communication

ad ho

c

ad ho

c

· Military networking: Tanks, soldiers, … · Finding out empty parking lots in a city, without asking a server· Search-and-rescue in an avalanche · Personal area networking (watch, glasses, PDA, medical appliance, …)· …


Factory floor automation


Disaster recovery


ad ho

c

ad ho

c

Car-to-car communication


Try to construct a network without infrastructure, using networking abilities of the participants This is an ad hoc network – a network constructed “for a special purpose”

Simplest example: Laptops in a conference room – a single-hop ad hoc network

Solution: (Wireless) ad hoc networks


Without a central infrastructure, things become much more difficult

Problems are due to Lack of central entity for organization available Limited range of wireless communication Mobility of participants Battery-operated entities

Problems/challenges for ad hoc networks


Without a central entity (like a base station), participants must organize themselves into a network (self-organization)

Pertains to (among others): Medium access control – no base station

can assign transmission resources, must be decided in a distributed fashion

Finding a route from one participant to another

No central entity ! self-organization


For many scenarios, communication with peers outside immediate communication range is required Direct communication limited because of distance, obstacles, … Solution: multi-hop network

Limited range ! multi-hopping

?


In many (not all!) ad hoc network applications, participants move around In cellular network: simply hand over to another base

station

Mobility ! Suitable, adaptive protocols

· In mobile ad hoc networks (MANET):· Mobility changes neighborhood

relationship · Must be compensated for· E.g., routes in the network have to be

changed · Complicated by scale

· Large number of such nodes difficult to support


Often (not always!), participants in an ad hoc network draw energy from batteries

Desirable: long run time for Individual devices Network as a whole

! Energy-efficient networking protocols E.g., use multi-hop routes with low energy consumption

(energy/bit) E.g., take available battery capacity of devices into account How to resolve conflicts between different optimizations?

Battery-operated devices ! energy-efficient operation


Heterogeneous nodes Do not need backbone infrastructure support

Self-creating not rely on a pre-existing fixed infrastructure

Self-organizing no predetermined topology

Self-administering no central control

creating a network “on the fly” Are easy to deploy Useful when infrastructure is absent, destroyed or impractical Infrastructure may not be present in a disaster area or war zone because there is no dependence on infrastructure, the network is robust and

low-cost. Finally, MANETs form the basis of all pervasive and ubiquitous computing.

MANETs characteristics


Military environments Soldiers, tanks, planes

Emergency operations Search-and-rescue Policing and fire fighting

Civilian environments Taxi cab network Meeting rooms Sports stadiums

MANETs Applications


Ad hoc networks Infrastructure less Multiple hop

Radio power limitation, channel utilization, and power-saving concerns

DCF(distributed coordination function) Cellular networks

Infrastructure-based one hop(uplink or downlink) PCF(pointed coordination function)

Ad hoc networks & Cellular networks


1.Spectrum allocation2.Self-configuration3.Medium access control (MAC)4.Energy efficiency5.TCP Performance6.Mobility management7.Security & privacy8.Routing protocols9.Multicasting10.QoS11.Service Location, Provision, Access

MANETs Challenges


In general, MANET routing protocols are expected to satisfy the following essential principles:

Tolerance of unexpected network faults (e.g. device and link failures) Flexibility to increasing traffic loads Minimal energy consumption (especially for smaller clients)

Mobile IP needs infrastructure Home Agent/Foreign Agent in the fixed network DNS, routing etc. are not designed for mobility

MANET No default router available “every” node also needs to be a router

Routing in MANET


Must be distributed Adaptive to frequent topology changes Must be localized, since global state maintenance

involves a huge state propagation control overhead Loop free and free from stale routes Convergence should be quick

Properties of good routing protocol in MANET


Mobility Topology highly dynamic due to movement of nodes

Ongoing sessions suffer frequent path breaks Even though wired network protocol find alternate

paths when a path breaks, the convergence is slow Bandwidth constraint Limited bandwidth imposes constraint on routing

protocols to maintain topological information Due to frequent changes in topology the control

overhead of keeping the topology current could be very high

Issues in Routing in MANET


Proactive or Table-driven protocols Traditional distributed shortest-path protocols Example: DSDV (destination sequenced distance

vector) Reactive or On-demand routing protocols

Determine route if and when needed Example: DSR (dynamic source routing)

Hybrid protocols Adaptive; Combination of proactive and reactive Example : ZRP (zone routing protocol) Hierarchical Geographical

MANET routing protocols


Ideally an ad hoc network routing protocol should be distributed in order to increase reliability assume routes as unidirectional links be power efficient. consider its security be hybrid protocols be aware of Quality of Service

Expected Properties of Routing


Is based on the idea of Bellman-Ford routing algorithm Every mobile station maintains a routing table that lists

all available destinations the number of hops to reach the destination the sequence number assigned by the destination node

A station transmits its routing table periodically if a significant change has occurred in its table from the last update

sent The routing table updates can be sent in two ways

full dump incremental update

Proactive routing protocols-DSDV


Example DSDV

MH4

MH6

MH5

MH8

MH7

MH1

MH1

MH3

MH2


Example DSDV

Destination Next hop Metric Sequence number

MH1 MH2 2 S406_MH1MH2 MH2 1 S128_MH2MH3 MH2 2 S564_MH3MH4 MH4 0 S710_MH4MH5 MH6 2 S392_MH5MH6 MH6 1 S076_MH6MH7 MH6 2 S128_MH7MH8 MH6 3 S050_MH8

Routing table at MH4


Example DSDV

Destination Metric Sequence number

MH1 2 S406_MH1MH2 1 S128_MH2MH3 2 S564_MH3MH4 0 S710_MH4MH5 2 S392_MH5MH6 1 S076_MH6MH7 2 S128_MH7MH8 3 S050_MH8

Advertisement from MH4


Example DSDV

Destination Next hop Metric Sequence number

MH1 MH6 3 S516_MH1MH2 MH2 1 S128_MH2MH3 MH2 2 S564_MH3MH4 MH4 0 S710_MH4MH5 MH6 2 S392_MH5MH6 MH6 1 S076_MH6MH7 MH6 2 S128_MH7MH8 MH6 3 S050_MH8

Routing table at MH4 (after MH1 moves)


Example DSDV

Destination Metric Sequence number

MH4 0 S710_MH4MH1 3 S516_MH1MH2 1 S128_MH2MH3 2 S564_MH3MH5 2 S392_MH5MH6 1 S076_MH6MH7 2 S128_MH7MH8 3 S050_MH8

Advertisement from MH4 (after MH1 moves)


Advantages

Routes available to all destinations Less latency in route set up

Disadvantages

Updates are propagated throughout the network Updates due to broken link (due to mobility) can lead to heavy

control traffic Even a small network with high mobility or large network with low

mobility can choke the network In order to get information about a particular destination node, a

node has to wait for a table update message initiated by the same destination node

This delay would result in stale routing information

DSDV: Advantages & Disadvantages


Reactive routing protocols are intended to maintain routing information about ‘active’ routes only. Routes are created when desired by the source node. Hence, the protocols are known as on-demand routing protocols.

However, no periodic routing advertisement messages are sent, thereby reducing network bandwidth overhead, particularly during periods when little or no significant host movement is taking place.

Reactive routing protocols- DSR


A node maintains route caches containing the source routes that it is aware of

The node updates entries in the route cache as and when it learns about new routes

route discovery route request packet contains

the address of the source the destination a unique identification number

route reply is generated by the destination an intermediate node with current information about the destination

route maintenance Route error packets are generated at a node when the data link layer

encounters a fatal transmission problem Acknowledgements, including passive acknowledgments

DSR


Source S initiates a route discovery by flooding Route Request (RREQ) Each node appends its own identifier when forwarding

RREQ Destination D on receiving the first RREQ, sends a

Route Reply (RREP) RREP sent on route obtained by reversing the route

appended in RREQ RREP includes the route from S to D, on which RREQ was

received by D S routes data using “source route” mechanism

Dynamic Source Routing (DSR)


Routing Discovery Example:


B

DE

F K

AI

C

H

JGSourceDestination


35



Route Discovery in DSR

B

A

S E

F

H

J

D

C

G

IK

Z

Y

Represents a node that has received RREQ for D from S

M

N

L

Source: Vaidya



B

A

S E

F

H

J

D

C

G

IK

Represents transmission of RREQ

Z

YBroadcast transmission

M

N

L

[S]

[X,Y] Represents list of identifiers appended to RREQ



B

A

S E

F

H

J

D

C

G

IK

• Node H receives packet RREQ from two neighbors: potential for collision

Z

Y

M

N

L

[S,E]

[S,C]



B

A

S E

F

H

J

D

C

G

IK

• Node C receives RREQ from G and H, but does not forward it again, because node C has already forwarded RREQ once

Z

Y

M

N

L

[S,C,G]

[S,E,F]



B

A

S E

F

H

J

D

C

G

IK

Z

Y

M

• Nodes J and K both broadcast RREQ to node D• Since nodes J and K are hidden from each other, their

transmissions may collide

N

L

[S,C,G,K]

[S,E,F,J]



B

A

S E

F

H

J

D

C

G

IK

Z

Y

• Node D does not forward RREQ, because node D is the intended target of the route discovery

M

N

L

[S,E,F,J,M]


Route Reply in DSR

B

A

S E

F

H

J

D

C

G

IK

Z

Y

M

N

L

RREP [S,E,F,J,D]

Represents RREP control message


Data Delivery in DSR

B

A

S E

F

H

J

D

C

G

IK

Z

Y

M

N

L

DATA [S,E,F,J,D]

Packet header size grows with route length


Route Error (RERR)

B

A

S E

F

H

J

D

C

G

IK

Z

Y

M

N

L

RERR [J-D]

J sends a route error to S along route J-F-E-S when its attempt to forward the data packet S (with route SEFJD) on J-D fails (an ACK mechanism has to be there in packet forwarding)


Uses: Finding alternate routes in case original route breaks Route reply from intermediate nodes

Problems: Cached routes may become invalid over time and due

to host mobility Stale caches can adversely affect performance

Route caching


Each node caches a new route it learns by any means When node S finds route [S,E,F,J,D] to node D, node S

also learns route [S,E,F] to node F When node K receives Route Request [S,C,G] destined

for node, node K learns route [K,G,C,S] to node S

DSR: Route caching


When node F forwards Route Reply RREP [S,E,F,J,D], node F learns route [F,J,D] to node D

When node E forwards Data [S,E,F,J,D] it learns route [E,F,J,D] to node D

A node may also overhear Data to learn routes

Route caching


Use of route caching

B

A

S E

F

H

J

D

C

G

IK

Z

M

N

L

[S,E,F,J,D][E,F,J,D]

[C,S]

[G,C,S]

[F,J,D],[F,E,S]

[J,F,E,S]

RREQ

When Z sends a route request for C, node K sends back a route reply [Z,K,G,C] to Z using a locally cached route

[K,G,C,S]RREP

Source: Vaidya


Routes maintained only between nodes who need to communicate reduces overhead of route maintenance

Route caching can further reduce route discovery overhead A single route discovery may yield many routes to

the destination, due to intermediate nodes replying from local caches

DSR: Advantages


Packet header size grows with route length due to source routing

Latency to discover a route before data can be sent Flood of route requests may potentially reach all

nodes in the network An intermediate node may send Route Reply using

a stale cached route, thus polluting other caches Inconsistency during route reconstruction phase

DSR: Disadvantages


MANET Routing Algorithms

FLOODING TABLE-DRIVEN ON-DEMAND HYBRID

+ Simplicity+ Multiple path to the destination- High Overhead- Lower reliability of data delivery : Because of broadcast behavior of flooding? Network properties :+ Rate of topology changes increase- Number of communications increases- Number of nodes in the network increases

+ Delay of route determination decreases-Communication overhead increases-Storage requirements increases? Network properties :+ Number of communication increases- Rate of topology changes increases- Number of nodes in the network increases

+ Communication overhead decreases but it is subject to number of communications in the network- Not optimal bandwidth utilization - Delay of route determination increases ? Network properties :+ Rate of topology changes increases- Number of communications increases- Number of nodes in the network increases

o Better trade-off between communication overhead and delay ? Network properties :o Rate of topology changes increaseso Number of communications increaseso Number of nodes in the network increases

advanced techniques of mobile ad hoc and wireless sensor networks chapter: 05-mobile computing...

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