Scalability of Mobile Ad Hoc Networks

Introduction

In this chapter, we discuss the concept of scalability applied to Mobile Ad hoc NETworks (MANET). MANETs are temporarily formed networks of mobile devices without the support of any infrastructure. One of the most important characteristics of MANETs is the unpredictable evolution of their configuration. The number of member nodes within a MANET can vary immensely over a short time interval, from tens to thousands and vice-versa. Therefore, the scalability of network formation and management, mobile middleware and applications is a key factor in evaluating the overall MANET effectiveness.

The large diversity and high penetration of mobile wireless devices make their networking a very important aspect of their use. By self-organizing in mobile ad hoc networks, heterogeneous devices can communicate, share their resources and services and run new and more complex distributed applications. Mobile applications such as multiplayer games, personal health monitoring, emergency and rescue, vehicular nets and control of home/office networks illustrate the potential of mobile ad hoc networks. However, the complexity of these networks brings new challenges regarding the management of heterogeneity, mobility, communication and scarcity of resources that all have an impact on scalability.

The scalability property of complex distributed systems does not have a general definition and evaluation strategy. Within the realm of MANET, scalability can refer to several aspects, from performance at the application layer to the way scarce resources are consumed. One example is the case where the mobile system is not scalable if batteries’ energy is exhausted by demanding management operations. A mobile middleware service is not scalable if it does not meet the mobile clients’ requirements with similar performance, irrespective of their number or mobility patterns.

All current MANET deployments or experiments involve a small number of devices, at most of the order of few tens, but, in the future, hundreds, thousands or even more devices will congregate and run the same application(s). Therefore it is essential to consider the strategies by which scalability will be provided to the network and application layers such that any number of devices and clients will be accommodated with the same performance. When used, mobile middleware systems will also be required to be scalable.

Following, the most important aspects of scalability with regard to mobile ad hoc networks will be reviewed considering how MANET can be managed cost-effectively and how an important application of large distributed systems, clustering, can be implemented in a scalable manner on MANET.

This chapter is organized as follows. The first Section discusses the management service of mobile ad hoc networks and innovative means for making it a scalable service. The rapid change of MANET membership impacts on the node address management. Additionally, frequent operations as split and merge require address management as well. Therefore, MANET management is mostly the management of node addresses.

As potentially large networks, MANET can be used as the infrastructure that supports mobile cluster computing. Consequently, the second section is dedicated to cluster computing on MANET and its related scalability issues.