Class 2 Routing

7/30/2019 Class 2 Routing

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Routing Protocols for Mobile

Ad Hoc Network

10/17/05


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Outline

Introduction to mobile ad hoc network

Ad hoc protocol routing requirementsCategorization of ad-hoc routing protocols

Representative Ad hoc protocols

Destination-sequenced Distance-vector(DSDV)

Ad-hoc On-demand Distance Vector(AODV)

Dynamic Source Routing (DSR)


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Mobile ad hoc network (MANET)

Self-configuring network of mobile stationsconnected by wireless links

Defined as Independent Basic Service Set(IBSS) in IEEE 802.11 standards

Peer-to-peer communication without usingAccess Point (AP) or any wired network

Dynamic topology

mobile nodes free to move randomly

mobile stations form an arbitrary topology


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Mobile ad hoc network (MANET)

Mobile station has router function

Peer to peer communication, no central control

Multi-hop routes between nodes

s

d

s

d


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Characteristics of MANETs

Dynamic topology

links formed and broken with mobility

Possibly uni-directional links

Constrained resources

battery power

wireless transmitter range

Network partitions

A B A

B

s d s

d


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Routing in MANETs

Goal:To find and maintain routes between

nodes in a dynamic topology with possiblyuni-directional links, using minimumresources.


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Ad Hoc Protocol Routing Requirements

Simple, reliable and efficient

Distributed but lightweight in natureQuickly adapts to changes in topology

Protocol reaction to topology changes shouldresult in minimal control overhead

Bandwidth efficient

Mobility management involving user locationand hand-off management


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Categorization of Ad-Hoc Routing

Protocols

Figure from Elizabeth M. Royer, CFigure from Elizabeth M. Royer, C--KKTohToh, A Review of Current Routing, A Review of Current Routing

Protocols for AdProtocols for Ad--Hoc Mobile Wireless Networks.Hoc Mobile Wireless Networks.


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Table Driven Based Routing

(Proactive)

Maintain table of all active links in network

Calculate the shortest path from table

Update table whenever nodes move

Immediate tell if node is reachable

Data can be sent immediately

Very high overheadsDSDV


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On-demand Routing(Reactive)

Find routes as needed

Cache information from other nodes requests

No static overhead

Slow start before transmitting data

AODV, DSR


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Representative Ad Hoc Routing

Protocols

Destination-Sequenced Distance-Vector

Routing (DSDV)- Proactive(table driven),next-hop routing, distance-vector

Ad hoc On-demand Distance-Vector Routing

(AODV)-reactive,next hop routing,distance-vector

Dynamic Source Routing (DSR)-reactive (ondemand),source routing,link state


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DSDV Routing

[Charles Perkins &Pravin Bhagwat]

Current in use on the MIT GRID projects

Route advertisements

Route table entry structure

Responding to topology changesRoute selection criteria

Summary


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Route Advertisements in DSDV

Each mobile node advertise its ownroute tables to its current neighbors

Routing tables update periodically toadapt the dynamic change and maintain

table consistency


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Route Table Entry Structure in DSDV

When advertisement, each mobile nodecontain its new sequence number and thefollowing information for each new route

The destinations address The number of costs (hops) required to reach the

destination

The sequence number of the informationreceived,originally stamped by the destination.


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Example of Advertised Table in DSDV

MHi-address for the mobile node, MH

4is the node

advertising the route table update

Table from Charles E.Perkins, AD HOC NetworkingTable from Charles E.Perkins, AD HOC Networking


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Responding to Topology Changes in DSDV

Two types of packets defined for route updates

full dump packets Carry all available routing information Size of multiple network protocol data units (NPDUs)

Transmitted infrequently during period of occasionalmovement

Incremental packets

Carry only information changed since last full dump Size of a NPDU

Transmitted more frequently

Additional table maintained to store the data from theincremental packets


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Route Selection Criteria

Routes are preferred if the sequence

numbers are newerIf the sequence numbers are the same, theone with better metric is preferred

Keep track of the settling time of routes-theweighted average time that routes to adestination will fluctuate before the route with

best metric is received (Why?)

R t S ttli Ti


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Route Settling Time

and SolutionA

CB

D

MN collection 1 MN collection 2

Problem

A initiated a route update with a new sequence number

Update from B arrives D 10 s before update from C

Metric of update from C is better (less hops)

Solutiondelay the broadcast of a routing by the length of thesettling time.

Exception:When broken link is found, broadcastimmediately


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Summary of DSDV Routing

Essentially a modification to Bellman-Fordrouting algorithm

Using sequence number to guarantee loop-freepaths

Relies on periodic exchange of routinginformation.

Inefficient due to periodic update transmissionseven no changes in topology

Overhead grows as O(n2) , limiting scalability


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Dynamic Source Routing (DSR)

[Dave J ohnson]

Internet drafts available on MANET webpage

Reactive (on demand)

Source routing

Based on link-state routing algorithm


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Route Discovery in DSR (1/6)

Sender floods RREQ through the network

Nodes forward RREQs after appending theirnames

Destination node receives RREQ andunicasts a RREP back to sender node

Y


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Represents node that has received RREQ originated

from S to D

B

A

S E

F

H

J

C

G

I

K

Z

Y

M

N

L

D

RREQ includes: the source IP address, the destination IP, a

unique request ID


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Route Discovery in DSR(3/6)

B

A

S E

F

H

J

D

C

G

I

K

Represents transmission of RREQ

Z

YBroadcast transmission

M

N

L

[S]

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


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B

A

S E

F

H

J

D

C

G

I

K

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]


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Route Discovery in DSR(6/6)

B

A

S E

F

H

J

D

C

G

I

K

Z

Y

M

Nodes J and K both broadcast RREQ to node D

N

L

[S,C,G,K]

[S,E,F,J]

Target Node Reaction


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Target Node Reaction

Node D examines its route cache, if a route to S found,use it as source route for RREP.Otherwise,

May perform its own route discovery to S,

piggyback the RREP on its own RREQ to S Simply reverse the sequence of hops in the

route record

Preferred by IEEE 802.11 that require abidirectional frame exchange

Avoids the overhead of a possible secondroute discovery

Tests the discovered route

Advantage : support asymmetric link


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Route Reply in DSR

B

A

S EF

H

J

D

C

G

I

K

Z

Y

M

N

L

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

Represents RREP control message

Route reply with its associated route record back to thesource node


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Summary of DSR Routing

Potentially larger overhead

Intended for moderate speed mobile nodes, sourcerouting, not scalable to large networks

No network topology changes, no overhead

Support asymmetric link

Allow nodes keep multiple routes to one destinationin their cache, faster route recovery


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1. RomitRoy Choudhury and Nitin H. Vaidya, Impact of

Directional Antennas on Ad Hoc Routing.2. Elizabeth M. Royer, C-K Toh, A Review of Current

Routing Protocols for Ad-Hoc Mobile Wireless

Networks.3. Charles E. Perkins, AD HOC Networking

References

Documents

Class 2 Routing