Routing protocols for mobile ad-hoc networks - Computer Networks ...

Routing protocols for mobile ad-hoc networks
We continue our series on mobile ad-hoc networks with a discussion of routing protocols, or how the information is
going to move throughout the network.
Mobile ad-hoc networks, also known as short-lived networks, are autonomous systems of mobile nodes forming
network in the absence of any centralized support. This is a new form of network and might be able to provide
services at places where it is not possible otherwise. Absence of fixed infrastructure poses several types of
challenges for this type of networking. Among these challenges is routing.
By routing, we mean process of exchanging information from one station to the other stations of the network.
Routing protocols of mobile ad-hoc network tend to need different approaches from existing Internet protocols,
since most of the existing Internet protocols were designed to support routing in a network with fixed structure. In
the academic and industrial world, those who think about such things have written quite a few papers proposing
various routing solutions for mobile ad-hoc networks. Proposed solutions could be classified into six types: table-
driven, on-demand, hierarchical, power-aware, geographical, and multicast protocols.
Table - driven protocols
Table-driven protocols are one of the old ways of acquiring routing in mobile ad-hoc networks. These protocols
maintain consistent overview of the network. Each node uses routing tables to store the location information of
other nodes in the network. This information is used to transfer data among various nodes of the network.
To ensure the freshness of the routing tables, these protocols adopts different sorts of mechanisms. One of the
adopted methods is broadcasting "hello," a special message containing address information, at fixed intervals of
time. On receiving this message, each node updates its routing tables with fresh locations information of other
participating nodes. Destination Sequence Distance Vector routing protocol (DSDV), Wireless Routing Protocol (WRP)
and Cluster-head Gateway Switch Routing (CGSR) are some of the popular table-driven protocols for mobile ad-hoc
networks.
Table-driven protocols might not be considered an effective routing solution for mobile ad-hoc network. Nodes in
mobile ad-hoc networks operate with low battery power and with limited bandwidth. Presence of high mobility,
large routing tables and low scalability result in consumption of bandwidth and battery life of the nodes. Moreover
continuous updates could create unnecessary network overhead.
On - demand routing protocols
Another in the family of routing protocols for mobile ad-hoc network is on-demand routing protocols. With on-
demand protocols, if a source node requires a route to the destination for which it does not have route information,
it initiates a route discovery process which goes from one node to the other until it reaches to the destination or an
intermediate node has a route to the destination.
It is the responsibility of the route request receiver node to reply back to the source node about the possible route
to the destination. The source node uses this route for data transmission to the destination node. Some of the better

known on-demand protocols are Ad-hoc On-demand Distance Vector routing (AODV), Dynamic Source Routing (DSR)
and Temporary Ordered Routing Algorithm (TORA).
These protocols differ on storing the previously known route information and on how they use the established route
data. Again, in a network with many participating nodes we may suffer with same sort of problems what we have
seen in table-driven protocols.
Conclusion
In conclusion, routing is one of the core issues in mobile ad-hoc network. An effective routing mechanism will be
helpful to extend the successful deployment of mobile ad-hoc networks. Current routing protocols provide routing
solutions up to a certain level, but are lacking the ability to handle other related issues.
Moreover most of these protocols have designed and implemented on small scale. If these protocols could be
extended further by taking into accounts other routing related factors we may come out with a standard routing
solution for mobile ad-hoc network.
Ad Hoc Networks
Introduction
An ad-hoc network is a self-configuring network of wireless links connecting mobile nodes. These nodes may be
routers and/or hosts. The mobile nodes communicate directly with each other and without the aid of access points,
and therefore have no fixed infrastructure. They form an arbitrary topology, where the routers are free to move
randomly and arrange themselves as required.
Each node or mobile device is equipped with a transmitter and receiver. They are said to be purpose-specific,
autonomous and dynamic. This compares greatly with fixed wireless networks, as there is no master slave
relationship that exists in a mobile ad-hoc network. Nodes rely on each other to established communication, thus
each node acts as a router. Therefore, in a mobile ad-hoc network, a packet can travel from a source to a destination
either directly, or through some set of intermediate packet forwarding nodes.
In a wireless world, dominated by Wi-Fi, architectures which mix mesh networking and ad-hoc connections are the
beginning of a technology revolution based on their simplicity.
Ad hoc networks date back to the Seventies. They were developed by the Defense Forces, to comply with a military
framework. The aim was to rapidly deploy a robust, mobile and reactive network, under any circumstances. These
networks then proved useful in commercial and industrial fields, first aid operations and exploration missions. Ad
hoc networks, also called peer-to-peer networks, still have a long way to go in order to be fully functional and
commercial, as it has its defects such as security and routing which we will discuss further.

Routing Protocols
Routing protocols between any pair of nodes within an ad hoc network can be difficult because the nodes can move
randomly and can also join or leave the network. This means that an optimal route at a certain time may not work
seconds later. Discussed below are three categories that existing ad-hoc network routing protocols fall into:
1. Table Driven Protocols
2. On Demand Protocols
3. Hybrid Protocols
Ad-hoc Mobile Routing Protocols
Diagram 1
1. Table Driven Routing Protocols, also known as Proactive Protocols, work out routes in the background
independent of traffic demands. Each node uses routing information to store the location information of other
nodes in the network and this information is then used to move data among different nodes in the network. This
type of protocol is slow to converge and may be prone to routing loops. These protocols keep a constant overview of
the network and this can be a disadvantage as they may react to change in the network topology even if no traffic is
affected by the topology modification which could create unnecessary overhead. Even in a network with little data
traffic, Table Driven Protocols will use limited resources such as power and link bandwidth therefore they might not
be considered an effective routing solution for Ad-hoc Networks. Fisheye State Routing is an example of a Table
Driven Protocol.
2. On Demand Routing Protocols, also known as Reactive Protocols, establish routes between nodes only when
they are required to route data packets. There is no updating of every possible route in the network instead it
focuses on routes that are being used or being set up. When a route is required by a source node to a destination for
which it does not have route information, it starts a route discovery process which goes from one node to the other
until it arrives at the destination or a node in-between has a route to the destination. On Demand protocols are
generally considered efficient when the route discovery is less frequent than the data transfer because the network

traffic caused by the route discovery step is low compared to the total communication bandwidth. This makes On
Demand Protocols more suited to large networks with light traffic and low mobility. An example of an On Demand
Protocol is Dynamic Source Routing.
3. Hybrid Routing Protocols combine Table Based Routing Protocols with On Demand Routing Protocols. They
use distance-vectors for more precise metrics to establish the best paths to destination networks, and report routing
information only when there is a change in the topology of the network. Each node in the network has its own
routing zone, the size of which is defined by a zone radius, which is defined by a metric such as the number of hops.
Each node keeps a record of routing information for its own zone. Zone Routing Protocol (ZRP) is an example of a
Hybrid routing protocol.
Security
Ad-hoc networks are highly vulnerable to security attacks and dealing with this is one of the main challenges of
developers of these networks today. The main reasons for this difficulty are;
"Shared broadcast radio channel, insecure operating environment, lack of central authority, lack of association
among nodes, limited availability of resources, and physical vulnerability."
Generally, when considering the security of a network, we examine it under the headings; availability,
confidentiality, authentication, integrity and non-repudiation. Availability refers to the fact that the network must
remain operational at all times despite denial of service attacks. Confidentiality ensures that certain information is
never disclosed to certain users. Authentication is the ability of a node to identify the node with which it is
communicating. Integrity guarantees that a message is never corrupted when transferred. Non-repudiation states
that the sender of the message cannot deny having sent it. An ad-hoc network has extra security requirements
caused by its lack of proper infrastructure and the dynamic relationship between the nodes in the network. Because
of the lack of infrastructure, accountability is very difficult to determine as there is "no central authority which can
be referenced when it comes to making trust decisions about other parties in the network."
The dynamic relationship between the nodes leaves very little opportunity for the nodes to form trust
relationships with each other. In an ad-hoc network, nodes must act as both terminals and routers for other
nodes. Because there are no dedicated nodes, a secure routing protocol is needed. Multi hop routing protocols are
usually employed. These can lead to problems due to non-cooperating nodes and denial of service attacks.
Denial of Service Attacks

Diagram 2
These problems are not easily solved and routing protocols for ad-hoc networks are still under active research.
Confidentiality is also a major issue in ad-hoc networks but it is one that can be solved more easily. Cryptography is
one of the most common and reliable means to ensure confidentiality.
"It is the study of the principles, techniques, and algorithms by which information is transformed into a disguised
version which no unauthorized person can read, but which can be recovered in its original form by an intended
recipient."
Another issue to be considered is protecting the information that is actually stored on the device as the more
portable the device, the easier it is to tamper with in general. We must also attempt to retain confidentiality of
identity and location which will become more important in the ubiquitous computing environment. Ad-hoc networks
require a high level of security, but because of the nature of these networks, this can often be difficult to
provide. Therefore, it is an issue which requires a lot more research if these networks are to continue to thrive.
The future of ad hoc networks
Mobile ad hoc networks are the future of wireless networks. Why? Because they're practical, versatile, simple, easy
to use and inexpensive! We will be living in a world where our network instantly updates and reconfigures itself to
keep us connected anywhere we go.
These networks provide a new approach for wireless communication and by operating in a license free frequency
band prove to be relatively inexpensive.
With the current trend of society's demand for information at out fingertips, we will see our future living
environments requiring communication networks between the many devices we use in day to day living, allowing
them to talk to each other.

For example devices like personal digital assistants and mobile phones being able to receive instant messages from a
home device. Such as a refrigerator sending a message to a PDA to update its shopping list; notifying that it's run out
of milk. Or washing machines and ovens sending a report to say the clothes are finished or the chicken's cooked.
Likewise, in education ad hoc networks may be deployed for student laptops interacting with the lecturer during
classes.
Also wireless public access for dense urban areas (Nokia RoofTopT): A wireless broadband solution for residential
markets, based on a multi-hop Ad-Hoc (mesh) networking.
Or similarly, ad hoc networks for cars, sending instant traffic reports and other information. Sensors and robots
forming multimedia network that allows remote visualization and control, multiple airborne routers (from tiny
robots to blimps) automatically providing connectivity and capacity where needed (e.g., at a football game); an ad
hoc network of spacecrafts around and in transit between the Earth and Mars.
Science fiction? Only time will tell.
Conclusion
Nokia RoofTopT Wireless Routing
Diagram 3
After researching Ad-hoc networks in depth, we believe that they will be the future of wireless networking. It is true
that performance suffers as the number of devices grows and large ad-hoc networks become difficult to route and
manage. However, much time is being devoted to achieving routing stability, and a few technical issues need to be
solved before they become common place. The area of ad hoc networks is a very fast growing area, and due to the
vast research in them, we are seeing these problems disappear and they are coming into a world of their own.

List of ad hoc routing protocols
An ad-hoc routing protocol is a convention, or standard, that controls how nodes decide which way
to route packets between computing devices in a mobile ad hoc network .
In ad-hoc networks, nodes are not familiar with the topology of their networks. Instead, they have to discover it. The
basic idea is that a new node may announce its presence and should listen for announcements broadcast by its
neighbours. Each node learns about nodes nearby and how to reach them, and may announce that it, too, can reach
them.
Note that in a wider sense, ad hoc protocol can also be used literally, that is, to mean an improvised and often
impromptu protocol established for a specific purpose.
The following is a list of some ad hoc network routing protocols.
1 Pro-active (table-driven) routing
2 Reactive (on-demand) routing
3 Flow-oriented routing
4 Hybrid (both pro-active and reactive) routing
5 Hierarchical routing protocols
6 Backpressure Routing
7 Host Specific Routing protocols
8 Power-aware routing protocols
9 Multicast routing
10 Geographical multicast protocols (Geocasting)
11 On-Demand Data Delivery routing
Pro-active (table-driven) routing
This type of protocols maintains fresh lists of destinations and their routes by periodically distributing routing tables
throughout the network. The main disadvantages of such algorithms are:
1. Respective amount of data for maintenance.
2. Slow reaction on restructuring and failures.

Examples of pro-active algorithms are:
Babel, a protocol inspired by DSDV with faster convergence and ETX link quality estimation. Free
implementation available.
B.A.T.M.A.N. – Better approach to mobile adhoc networking.
DSDV (Highly Dynamic Destination-Sequenced Distance Vector routing protocol)
HSR (Hierarchical State Routing protocol)
HSLS The hazy-sighted link-state algorithm.
This algorithm is based on empirical and theoretical studies to limit link-state traffic while achieving practical
link mobility. It avoids the message flooding of DSR, OLSR and AODV by growing the range of the link-state
updates twofold for each twofold expansion of time. It has a practical large network in place at CuWIN.
IARP (Intrazone Routing Protocol/pro-active part of the ZRP)
Linked Cluster Architecture | LCA (Linked Cluster Architecture)
WAR (Witness Aided Routing)
OLSR Optimized Link State Routing Protocol
Reactive (on-demand) routing
This type of protocols finds a route on demand by flooding the network with Route Request packets. The main
disadvantages of such algorithms are:
1. High latency time in route finding.
2. Excessive flooding can lead to network clogging.
Examples of reactive algorithms are:
SENCAST –A Scalable Protocol for Unicasting and Multicasting in a Large Ad hoc Emergency Network,
International Journal of Computer Science and Network Security.
Reliable Ad hoc On-demand Distance Vector Routing Protocol
Ant-based Routing Algorithm for Mobile Ad Hoc Networks – ARA – the ant-colony based routing algorithm
for manets,
Admission Control enabled On demand Routing (ACOR) –
Ariadne – A Secure On-Demand Routing Protocol for Ad Hoc Networks
Associativity-Based Routing – A Novel Distributed Routing Protocol To Support Ad hoc Mobile Computing
Ad hoc On-demand Distance Vector(AODV)
Ad hoc On-demand Routing Protocol (AORP)
Ad hoc On-demand Multipath Distance Vector
Backup Source Routing
Dynamic Source Routing
Flow State in the Dynamic Source Routing
Dynamic NIx-Vector Routing
Dynamic Manet On-demand Routing
Endaira: It is on demand source routing protocol and it is designed to address the hidden channel attack in
ariadne.