CONTENTS

Introduction What are MANETs? MANET protocols Reactive vs. Proactive Ad Hoc routing protocols Reactive Routing Protocol Proactive Routing Protocol Comparision simulation Conclusion References

An autonomous system of mobile routers connected by wireless links.

The routers are free to move randomly and organize themselves arbitrarily.

A MANET is a wireless mobile network that is self-forming, self maintained, and self-healing.

Nodes stay connected even as the network topology changes. Each node needs to act as a router to relay packets to nodes

out of direct communication range.

Introduction

Mobile Ad-Hoc Networks

A Collections of mobile nodes dynamically forming a temporary network. Nodes are arbitrarely located. Each node in a network acts as a router. Goal: Correct and efficient route establishment to facilitate communication.

Characteristics Dynamic topology.

Variable capacity links. Energy-constrained mobile nodes. Weakened physical security.

Why traditional protocols are not suitable for MANETs?

No pre-existing infrastructure. Variable capacity links. Dynamic topologies. Limited physical security.

MANETs Use

For military and rescue use. Internet / intranet hot spots in public transportation. Information distribution for meetings, seminars etc. New mobile devices are invented constantly and used

various ways.

MANET Protocols

Ad-Hoc Routing Protocols

Reactive Proactive

TBRPF DSDV AODV DSR

DSR Designed for multihop wireless

ad-hoc networks. Two major phases: Route discovery : used to discover new source

routes across multiple network hops destinations in an ad-hoc network

Route Maintainance: When a node receives a Route-Request, it first searches its route

cache for the target node. If route is found, the node can send a Route-Reply to the initiator. Preventing Route-Reply storms: To avoid storms, the DSR uses a random delay before a node

can send a Route-Reply.

d = H * (h – 1 + r)• H, small const. Delay• h, number of hops is source route• r, 0 or 1

AODV An embedded MANET protocol works dynamically to establish and maintain routes AODV algorithm enables dynamic, self-starting, multihop routing

between participating mobile nodes AODV allows mobile nodes obtain routes quickly for new destinations. respond to link breakages changes in network topology in a timely manner.

Messages for route discovery Message types defined by AODV are

RREQs RREPs RERRs

Route Creation: When a source node does not have a route for a required destination. AODV initiates a route request/route reply cycle by broadcasting a

route request (RREQ) packet across the wireless network. Route Deletion: A route will remain active as long as data continues to travel across

the route If a route becomes inactive for a period of time, the route will be

deleted. Sequence Numbers: To avoid routing loops and to measure the “freshness” of route

information

DSDV Developed at the IBM, in 1996. Uses the modified Bellman-Ford algorithm. This is a Proactive Routing protocol, where the route is always

available. Operation: Mobile nodes maintain routes to all possible destinations. Hop counts are used as routing metrics. The node assigns sequence numbers to distance vector updates.

which updates contain information about the neighbors.

TBRPF Provides hop-by-hop routing

along shortest paths to each destination.

Using a modification of Dijkstra's algorithm,each node computes a source tree.

Two main modules: neighbor discovery module routing module.

Neighbor Discovery: TND protocol allows each node i to quickly detect the neighbor nodes

j such that ij and ji exists. Nodes with multiple interfaces run TND separately on each interface Routing Module: Each node reports only part of its source tree to neighbors. Each node reports RT to neighbors in periodic topology updates and reports changes to RT in more frequent differential updates Periodic updates inform new neighbors of RT Differential updates ensure the fast propagation of each topology

update to all nodes that are affected by the update.

Comparison Simulations Features of protocols: AODV DSR TBRPF

Loop-freedom Yes Yes No

Multiple routes No Yes Possible

Unidirectional link support

Possible Yes No

Multicast Possible No No

Periodic Broadcast Possible No Yes

Maximum No. of nodes <100 200 <200

Expiration of routing info. Yes No Yes

Category Reactive Reactive Proactive

Summarizing the resultsa) Low mobility, low traffic

AODVDSR TBRPF

Packet delivery ratio

High High High

End to end delay

Middle Middle Middle

Routing overhead

Low Low Middle

Path optimality

Middle Middle Very good

b) High mobility, High traffic

AODVDSR TBRPF

Packet delivery ratio

Middle Middle High

End to end delay

Middle Middle Middle

Routing overhead

Very High

Middle Middle

Path optimality

Middle Low Good

Problems of the particular protocols AODV uses more, but smaller routing control packets worse for a higher load. DSR has some problems concerning the cache usage: multiple routing the source-routing principle TBRPF packet loss, waste of bandwidth and causes other

problems.

Conclusion protocol max throughput DSDV small sized DSR medium sized AODV large sized fundamental questions to answer Scalability? Energy efficiency? Security? Combination of physical, data-link and network layer?

References

Websites: http://www.ietf.org/rfc/rfc3561.txt http://www.isi.edu/ http://www.cs.technion.ac.il/

Books: Bertsekas, D. and R. Gallager, "Data

Networks, Prentice-Hall", 1