The Hexell Project

Introduction

Hexell is an architecture integrating a network routing protocol and a service discovery protocol for wireless Mobile Ad-Hoc Networks. I became interested in researching for protocols for MANETs because of their totally unpredictable and dynamic characteristics (explained later). Developing protocols for such networks is a very challenging task requiring intricate considerations.

Both the network routing protocol and the service discovery protocol are extremely important for the operation of MANETs. A network routing protocol is the layer of protocol that is responsible for route discovery and maintenance, as well as packet forwarding. A service discovery protocol allows service providers to advertise their services, which are applications offered by providers that users can interact with. This kind of protocol also allows users to automatically discover services. This is especially important in a wireless environment, where users are often only equipped with devices with limited resources.

Concepts

A MANET is a mobile wireless network without infrastructure support. Its dynamic nature and infrastructure-less features presented many challenges to protocol researchers for this kind of network. A network routing protocol is important for the operation within MANETs and has been a crucial topic for researchers involved with MANETs. Service discovery protocols are also essential for resource-lacking mobile users in a wireless network. These two topics are crucial for users to operate in MANETs properly.

Conventionally, the layers of network protocols are researched separately to allow researchers to concentrate on one layer at a time by clearly defining the responsibility of each layer. Under this kind of assumption, typically a higher layer does not need be concerned with how the network is modeled at a lower layer. For example, TCP operates without the knowledge and direct feedback of how Ethernet works at a lower level. Network researchers for MANETs automatically follow this strict paradigm when trying to develop protocols for MANETs.

Furthermore, current service discovery protocols do not provide proper ways to distinguish duplicate services and do not support different interaction techniques. These protocols only try to discover services and do not assume the responsibility of allowing users to select and interact with these services.

In this work, a new paradigm for developing a service discovery protocol that is based on the network model maintained by the lower layer network routing protocol has been developed. The network protocol is responsible for maintaining the structure of the network, discover unknown routes, and maintain current routes. The Hexell network routing protocol is based on the model of dividing the environment into hexagon cells. Figure 1 depicts a hexagon mapped network. Each node is aware of its location and the cell it belongs to. Furthermore, there is a gateway in each cell that is responsible for maintaining routes and forwarding packets. These gateways can be any node and are elected when necessary. Gateways in Hexell form a “virtual backbone” that supports the network. The service discovery protocol is built based on this network model and gateways are also used as directories that handle service discovery tasks. Directories are responsible for handling service advertisement and service query. The concept of directories is commonly used in service discovery protocols for traditional wired networks since it is more efficient and more scalable. However, this concept is absent from MANET protocols since the requirement of establishing directories contradicts the infrastructureless nature of MANETs. The service discovery protocol receives notifications from the network routing protocol and has knowledge of each node’s location status. This concept improves efficiency of a node’s overall operation within the MANET without compromising the capability the system.

Figure 1: A hexagon mapped network

This work has also led to the development of a comprehensive service discovery solution by not only handling service discovery, but also performing selection and facilitating interaction with services. In this system, once potential services are discovered, the protocol uses mobile agents to facilitate the selection process by compiling context-aware information. Users have control of how context information is evaluated and how to use such information to select services. Moreover, the service discovery protocol helps user with different types of interaction methods.

Implementation

Currently Hexell is implemented using J-Sim. J-Sim is a component-based, compositional simulation environment. This platform is chosen because it is component based, cleaner than NS2, and being Java based. More information on J-Sim can be found here. Furthermore, Ansim is used to generate all the movements of mobile nodes in the simulation. More information on Ansim can be found here.

Publications

• Tyan, J., Mahmoud, Q.H.: A Comprehensive Service Discovery Solution for Mobile Ad Hoc Networks. In ACM/Kluwer Journal of Mobile Networks and Applications (MONET), Vol. 10 (8), August 2005, pp. 423-434.
• Tyan, J., Mahmoud, Q.H.: A Network Layer Based Architecture for Service Discovery in Mobile Ad Hoc Networks. In Proceedings of the 17th Annual IEEE Canadian Conference on Electrical and Computer Engineering (CCECE 2004), Niagara Falls, ON, Canada, May 2004, pp. 1379-1384.