Cooperative Cache Replacement Policy for MANETs

Introduction

MANETs stands for “Mobile Ad Hoc Networks”. A MANETs is a type of ad hoc network that can change locations and configure itself on the fly. With the increase of portable devices as well as progress in wireless communication, ad-hoc networking is gaining importance with the increasing number of widespread applications. Ad-hoc networking can be applied anywhere where there is little or no communication infrastructure or the existing infrastructure is expensive or inconvenient to use. Because MANETs are mobile, they use wireless connections to connect to various networks. Some MANETs are restricted to a local area of wireless devices (such as a group of laptop computers), while others may be connected to the Internet. For example, A VANET (Vehicular Ad Hoc Network) is a type of MANETs that allows vehicles to communicate with roadside equipment. While the vehicles may not have a direct Internet connection, the wireless roadside equipment may be connected to the Internet, allowing data from the vehicles to be sent over the Internet. The vehicle data may be used to measure traffic conditions or keep track of trucking fleets. Because of the dynamic nature of MANETs, they are typically not very secure, so it is important to be cautious what data is sent over a MANETs. Figure 1 shows two different scenarios of a typical structure of MANETs.

Figure 1.

A typical MANETs

In adhoc networks, mobile nodes communicate with each other using multi-hop wireless links. As there is no infrastructure support, mobile nodes cooperate with each other to forward data. Each node acts as a router, forwarding data packets for other nodes and mobile nodes have peer to peer connection among themselves. Most previous research in ad hoc networks focused on the development of dynamic routing protocols that can efficiently find routes between two communicating nodes. Although routing is an important issue, but the ultimate goal of adhoc networks is to provide mobile nodes with access to information.

However, MANETs are limited by intermittent network connections, restricted power supplies, and limited computing resources. These restrictions raise several new challenges for data access applications with the respects of data availability and access efficiency. In adhoc networks, due to frequent network partition, data availability is lower than that in traditional wired networks. Cooperative caching provides an attractive solution for this problem. Cooperative caching is a technique that allows the sharing and coordination among the mobile nodes.

However, the movement of nodes, limited storage space and frequent disconnections limit the availability. By the caching of frequently accessed data in adhoc networks we can improve the data access, performance and availability. Due to mobility and resource constraints of adhoc networks, caching techniques designed for wired network may not be applicable to ad hoc networks.

Consider a scenario in which mobile devices always retrieve data from the data center. This may result in a large amount of traffic in the network. This, apparently, is undesirable as traffic directed to the data center consumes wireless bandwidth as well as power of mobile devices. In addition, a mobile host suffers from high access latency if it is distant from the data center, and packet loss probability for long-distance data access is high. Furthermore, traffic near the data center will be heavy, and this leads to a potential performance bottleneck. These problems are more pronounced when the network size is large, which results in poor scalability of the system. The above observations motivate us to investigate a new data caching technique for MANETs. With data cached in mobile nodes, a data request may be satisfied by a nearby mobile node, instead of being serviced by the data center. By cooperative caching the data we can:

• 1.

  Improve the data availability.

• 2.

  Improve the data access time.

• 3.

  Reduce the traffic near the data center.

• 4.

  Reduce the consumption of bandwidth.

In general, a good cooperative cache management technique for MANETs should address these issues: