Mobile ad hoc networks (manets)

Mobile Ad-hoc Networks (manets)
By Donatas Sumyla

Table of Contents
1. Introduction

Introduction
 Importance of networking
 Computer network – system for
communication between computers (fixed,
temporary)
 History starts with Advanced Research
Projects Agency (ARPA) in 1962
 1969 the beginning of ARPANet which
connected University of LA, SRI, University
of California at Santa Barbara, and the
University of Utah

Mobile Ad-hoc Network
 Self-configuring network of mobile routers (and
associated hosts) connected by wireless links
 This union forms a random topology
 Routers move randomly free
 Topology changes rapidly and unpredictably
 Standalone fashion or connected to the larger
Internet
 Suitable for emergency situations like natural or
human-induced disasters, military conflicts,
emergency medical situations, etc.

Mobile Ad-hoc Network
 Ad-hoc network versus Mobile Ad-hoc
network
 Increase of mobile applications
 Additional challenges
 Changes to the network topology
 Need of extreme network flexibility
 Answer = Mobile Ad-hoc Network

 While MANETs are self contained, they can
also be tied to an IP-based global or local
network – Hybrid MANETs

History of MANETs
 Earliest MANETs were called “packet radio”
networks, sponsored by DARPA (1970)
 These packet radio systems predated the Internet
and were part of motivation of the original IP suite
 Later DARPA experiments included the Survivable
Radio Network (SURAN) project (1980s)
 1990s – the advent of inexpensive 802.11 radio
cards for personal computer
 Current MANETs are designed primary for military
utility; examples include JTRS (Joint Tactical
Radio System) and NTDR (Near-Term Digital
Radio).

Routing Protocols for MANETs
 Two types of routing protocols:
1. Table-Driven Routing Protocols
 Destination-Sequenced Distance-Vector Routing
(DSDV)
 Clusterhead Gateway Switch Routing (CGSR)
 The Wireless Routing Protocol (WRP)
1. Source-Initiated On-Demand Routing
Protocols
 Ad-Hoc On-Demand Distance Vector Routing
(AODV)
 Dynamic Source Routing (DSR)
 Temporally-Ordered Routing Algorithm (TORA)
 Associativity-Based Routing (ABR)

Destination-Sequenced Distance-
Vector Routing (DSDV)
 Table-driven algorithm based on the
classical Bellman-Ford routing mechanism
 Improvements – freedom of loops in routing
tables
 Routing is achieved by using routing tables
maintained by each node
 The main complexity in DSDV is in
generating and maintaining these routing
tables

Clusterhead Gateway Switch
Routing (CGSR)
 Uses DSDV as an underlying protocol and Least
Cluster Change (LCC) clustering algorithm
 A clusterhead is able to control a group of ad-
hoc hosts
 Each node maintains 2 tables:
1. A cluster member table, containing the cluster head
for each destination node
2. A DV-routing table, containing the next hop to the
destination
 The routing principle:
 Lookup of the clusterhead of the destination node
 Lookup of next hop
 Packet send to destination
 Destination clusterhead delivers packet

Routing (CGSR)

Routing (CGSR)
 Drawbacks: too frequent cluster head
selection can be an overhead and cluster
nodes and Gateway can be a bottleneck

The Wireless Routing Protocol
(WRP)
 Table-based protocol with the goal of maintaining routing
information among all nodes in the network
 Each node is responsible for four tables:
 Distance table
 Routing table
 Link-cost table
 Message retransmission list (MRL) table
 Link exchanges are propagated using update messages
sent between neighboring nodes
 Hello messages are periodically exchanged between
neighbors
 This protocol avoids count-to-infinity problem by forcing
each node to check predecessor information
 Drawbacks: 4 tables requires a large amount of memory
and periodic hello message consumes power and
bandwidth

Source-Initiated On-Demand
Routing Protocols
Ad-Hoc On-Demand Distance Vector Routing
(AODV)
 Builds on DSDV algorithm and the improvement is on
minimising the number of required broadcasts by creating
routes on an on-demand basis (not maintaining a complete
list of routes)
 Broadcast is used for route request
 Advantages: uses bandwidth efficiently, is responsive to
changes in topology, is scalable and ensures loop free
routing
 Drawbacks: nodes use the routing caches to reply to route
queries. Result: “uncontrolled” replies and repetitive
updates in hosts’ caches yet early queries cannot stop the
propagation of all query messages which are flooded all
over the network

Dynamic Source Routing (DSR)
 Based on the concept of source routing
 Mobile nodes are required to maintain route caches that
contain the source routes of which the mobile is aware
 2 major phases:
 Route discovery – uses route request and route reply packets
 Route maintenance – uses route error packets and
acknowledgments
 Advantages: No periodic hello message and fast recovery -
cache can store multiple paths to a destination
 Drawbacks: the packets may be forwarded along stale
cached routes. It has a major scalability problem due to the
nature of source routing. Same as AODV, nodes use the
routing caches to reply to route queries

Temporally-Ordered Routing
Algorithm (TORA)
 Highly adaptive, loop-free, distributed
routing algorithm based on the concept of
link reversal
 Proposed to operate in a highly dynamic
mobile networking environment
 It is source initiated and provides multiple
routes for any desired source/ destination
pair
 This algorithm requires the need for
synchronized clocks

Temporally-Ordered Routing
Algorithm (TORA)
 3 basic functions:
 Route creation
 Route maintenance
 Route erasure
 Advantages: provides loop free paths at all
instants and multiple routes so that if one path is
not available, other is readily available. It
establishes routes quickly so that they may be
used before the topology changes.
 Drawbacks: exhibits instability behavior similar to
"count-to-infinity" problem in distance vector
routing protocols.

Associativity-Based Routing (ABR)
 Free from loops, deadlock, and packet duplicates,
and defines a new routing metric for ad-hoc mobile
networks
 Each node generates periodic beacons (hello
messages) to signify its existence to the neighbors
 These beacons are used to update the
associativity table of each node
 With the temporal stability and the associativity
table the nodes are able to classify each neighbor
link as stable or unstable

 ABR consists of 3 phases:
 Route Discovery
 Route Repair/Reconstruction
 Route Delete

 If node A has in his Route Cache a route to
the destination E, this route is immediately
used. If not, the Route Discovery protocol is
started

 Advantages: free from duplicate packets
 Drawbacks: Short beaconing interval to
reflect association degree precisely

Signal Stability Routing (SSR)
 descendent of ABR and ABR predates SSR
 it selects routes based on signal strength
between nodes and on a node’s location
stability thus offers little novelty
 SSR route selection criteria has effect of
choosing routes that have ‘stronger’
connectivity and it can be divided into:
 Dynamic Routing Protocol (DRP) or
 Static Routing Protocol (SRP)

Signal Stability Routing (SSR)
 DRP is responsible for maintenance of
signal stability table and routing table
 SRP processes packets by passing the
packets up the stack if it is the intended
receiver and forwarding the packet if it is not
 Advantages: to select strong connection
leads to fewer route reconstruction
 Drawbacks: long delay since intermediate
nodes can’t answer the path (unlike AODV,
DSR)

Mobile ad hoc networks (manets)

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