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Ad-Hoc On-Demand Distance Vector(AODV) Routing

Charles E. Perkins, Elizabeth M. Belding-Royer, and Samir Das,Proceedings of IEEE WMCSA'99,New Orleans, LA,February 1999

Presented by (Byungho Min)17 April, 2006

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Ad-Hoc On-Demand Distance Vector 2

Contents Ad-Hoc Network Routing Constraints

Ad-Hoc On-Demand Distance Vector (AODV) AODV Algorithm

Path Discovery

Route Table Management

Path Maintenance

Local Connectivity Management

Simulation and Results

Current Status and Future Work

Conclusion

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Ad-Hoc Network Routing Constraints No Infrastructure Support

No Specialized Routers (Physically) No Fixed Routers

Frequent Topology Change Mobility

Problems Due to Wireless Media Bandwidth Range of Communication

Collisions Due to Broadcasting Asymmetric One-Way Links

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Ad-Hoc On-Demand Distance Vector(AODV)

A Source Initiated Routing Protocol

Premise Symmetric Links Features

Pure On-Demand Acquisition Broadcast only when necessary

Notion of Active Paths No centralized topological knowledge Neighborhood detection

Topological Maintenance Uses Hello to identify neighbors

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AODV Algorithm Path Discovery

Reverse Path Setup Forward Path Setup


Path Maintenance Local Connectivity Management

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Path Discovery When?

No Information on Some Node to Which Communication IsRequested

Each Node Has Two Counters

Path Discovery Process Source Node Broadcasts a Route Request (RREQ) Packet to

Its Neighbors

Neighbors Forward the Request to Their Neighbors, and soon until Either the Destination oran Intermediate Node with a Fresh Enough Route to theDestination Is Located

broadcast_idnode sequence number

Unique!

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More on RREQ broadcast_idIs Incremented for New RREQ

RREQ from Same Node with Same broadcast_idWillNot Be Broadcasted More than Once

AB

C

D

B wont rebroadcast this RREQ

Node A wants to contact node D,

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Route Requests

B

A

S E

F

H

J

D

C

G

I

K

Represents transmission of RREQ

Z

Y

Broadcast transmission

M

N

L

This example is takenfrom Wireless Internet

Class Material

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Route Requests (Contd)

B

A

S E

F

H

J

D

C

G

I

K

Represents links on Reverse Path

Z

Y

M

N

L

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Reverse Path Setup

B

A

S E

F

H

J

D

C

G

I

K

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

Z

Y

M

N

L

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Reverse Path Setup (Contd)

B

A

S E

F

H

J

D

C

G

I

K

Z

Y

M

N

L

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Reverse Path Setup

B

A

S E

F

H

J

D

C

G

I

K

Z

Y

Node D does not forward RREQ, because node Dis the intended target of the RREQ

M

N

L

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Route Reply

B

A

S E

F

H

J

D

C

G

I

K

Z

Y

Represents links on path taken by RREP

M

N

L

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Forward Path Setup

B

A

S E

F

H

J

D

C

G

I

K

Z

Y

M

N

L

Forward links are setup when RREP travels alongthe reverse path

Represents a link on the forward path

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Data Delivery

B

A

S E

F

H

J

D

C

G

I

K

Z

Y

M

N

L

Routing table entries used to forward data packet.Route is notincluded in packet header.

Data

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Path Discovery (Contd) RREQ Generates Backward Path to Source

RREP Generates Forward Path to Destination

A

B

C

D

E

F

G

RREQ

RREQ

RREP

RREP

1. G

2. G

route

route2. G route G RREQ broadcast

3. B A RREQA backward pathRREQ re-broadcast 4. G RREQ seq#

A backward path

route RREP unicast

5. D RREPG forward path,A backward path RREP unicast

6. A RREPG forward path

unicast

P

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Route Request (RREQ)

Message Format0 1 2 30 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| Type |J|R|G|D|U| Reserved | Hop Count |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| RREQ ID (broadcast id) |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| Destination IP Address |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| Destination Sequence Number |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| Originator IP Address |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| Originator Sequence Number |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Unique+

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Route Reply (RREP)

Message Format0 1 2 30 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| Type |R|A| Reserved | Prefix Sz | Hop Count |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| Destination IP address |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| Destination Sequence Number |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| Originator IP Address |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| Lifetime |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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Route Request Expiration Timer Purges Reverse Paths That Do Not Lie on Active Route

active_route_timeout

Is Used to Determine If Neighboring Node Is Active i.e.Sends at Least One Packet in This Time

Route Cache Timer Purges Inactive Routes

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Each Route Table Entry Contains Destination Next Hope Number of Hops

Sequence Number for the Destination Active Neighbors for This Route Expiration Time for the Route Table Entry

Route Table Management (Cont

d)

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When a Route Entry Is Used to Transmit Data fromSource to Destination,

Timeoutfor Each Entry IsReset to Current Time + active_route_timeout

When a New Route Is Available, Route Table Will BeUpdated Only If New Route Has Larger dest_sequence_#

Or

Same dest_sequence_#but with Smaller hop_cntto theDestination

Route Table Management (Cont

d)

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If Source Node Moves during an Active Session

It Can Redo Path Discovery If Destination or Intermediate Nodes Move A Special RREP Is Sent to Affected Source Nodes On link breakage, affected node propagates an unsolicited

RREP to all active neighbors

Source May Restart Route Discovery Process

Path Management

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If Link between C and D Is Broken, a Special RREPWill Be Sent to B and E by C C Will Increase Its dest_sequence_#by 1 and Set hop_

countto

) Then B and E Will Send This RREP to Its Active

Neighbors F and G At the End, All Active Source Nodes Are Notified When Source Finds Out a Link to Destination Is

Broken, and It Likes to Rebuild the Path toDestination, Source Will Send a RREQ with Lastdest_squence_#+ 1

A B C D

100 100100 100

EFG

Path Management Example

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Local Connectivity Management Two Ways for a Node to Find Its Neighbors

Receiving Broadcast from Its Neighbors

Send Its Neighbors Hello Messages Containing Its Identityand Sequence Number Sequence number is not changed for hello message Nodes can not rebroadcast hello messages (TTL=1)

Local Connectivity Is Changed If Receiving a Broadcast or a Hello from a New Node Failing to Receive allowed_hello_lossConsecutive Hello

Message from a Node Previously in the Neighborhood

Neighbors Only Communicate When Heard EachOthers Hello Message It Ensures the Link Is Bidirectional

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Simulations and Results

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Simulations and Results

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Current Status and Future Work Current Status

Multicast RREQ, RREP, and Multicast validation message

Future Works Intermediate Node Route Rebuilding

Try repair before link failure notification

Elimination of Hello Messages

Locality of Association and QoS

Improve bandwidth utilization by varying route propagationwithout indiscriminate relays

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Conclusion Storing Only the Needed Routes

Minimized Need for Broadcast Reduced Memory Requirements and Needless

Duplications

Quick Response to Link Breakage in Active Routes Loop-Free Routes Maintained by Use of Destination

Sequence Numbers

Scalable to Large Populations of Nodes

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Thank you!

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