Gary Clemo

Toward Formal Verification of 802.11 MAC Protocols: Verifying a Petri-Net Model of 802.11 PCF

The delivery of traffic with stringent Quality of Service (QoS) requirements over wireless local area networks (WLAN) is a vital research topic. A solution is to adopt centralized control functions, which allocate part of the bandwidth to polling traffic and part to contending traffic. Reliable means of performing this allocation are required as this allocation directly determines how well the two forms of traffic can coexist. In an earlier publication we presented an extended Petri-net model of an IEEE802.11 centralized control scheme, and used this model in the manner of a simulation tool to analyze performance, promising analysis of the model to come. Here we perform verification on aspects of the model to verify key properties of the system, something that is only possible by virtue of the strong mathematical basis of Petri-nets.

Enhancing IEEE802.11 DCF using Genetic Programming

This paper introduces a method of designing optimized MAC layer algorithms using genetic programming. By evolving entire algorithmic behaviour rather than optimizing a set of values to tune a parameterized design, a much wider space of behaviour can be explored automatically. This technique is illustrated using the variation of contention window size that is part of the distributed coordination function of 802.11. When applied to the example of a variable sized network under saturated load this approach produces expressions that comfortably outperform the standard 802.11b behaviour. Also, despite being automatically generated, these solutions achieve the throughput performance of the best enhancements to this aspect of the protocol

Petri-nets for formal verification of MAC protocols

Full or partial reconfiguration of communications devices offers both optimised performance for niche scenario-specific deployments and support for de-regulated radio spectrum management. The correctness of the protocols or protocol-enhancements being deployed in such a dynamic and autonomous manner cannot easily be determined through traditional testing techniques. Formal description techniques are a key verification technique for protocols. The Petri-net formal description technique offers the best combination of intuitive representation, tool-support and analytical capabilities. Having described key features and analytical approaches of Reference-nets (an extended Petri-net formalism), a case study is presented applying this approach to a contemporary research area: IEEE 802.11 centralised control mechanisms to support delay-sensitive streams and bursty data traffic. This case study showcases the ability both to generate performance-oriented simulation results and to determine more formal correctness properties. The simulation results allow comparison with published results and show that a packet-expiration mechanism places greater demands on the contention-free resource allocation, while the mathematical analysis of the model reveals it to be free of deadlock and k-bounded with respect to resources. The work demonstrates the potential that the Petri-net formal method has for analysing process and protocol models to support reconfigurable devices.

The use of service discovery to support reconfigurable terminals

To date a significant amount of work has been conducted into the technologies required to realise reconfigurable terminals. Much of this work has been focused on adaptable hardware or lower-level protocols. However, more effort is now being directed towards reconfiguration at the system and application levels. As a result, the reconfigurable terminal is beginning to be thought of as a collection of interacting objects in a complex, distributed system. Within this context, middleware becomes an important tool to support reconfiguration, as it conceals the complexities of distributed, heterogeneous environments. One application of middleware is service discovery, a set of protocols and techniques to simplify service advertisement, location and interaction. This paper examines how service discovery might be used to support reconfiguration within a terminal environment.

Towards Integrated Wireless Systems: Inter-Mode Monitoring Techniques

Inter-operation between the heterogeneous wireless networks and systems available now and in the future is of considerable interest. Fundamental to such work is the ability to discover available alternative systems, and to monitor these modes to determine whether they are more attractive in some way than the current system. This paper presents a survey of different solutions to the problem of multi-mode detection and monitoring including blind unassisted techniques, co-operative devicefederation approaches and higher-layer mechanisms and suggests future research directions in this area.

Applications of delegation schemes for securing future reconfigurable terminals

The main goal of this paper is to address applications of secure mobile delegation for future reconfigurable terminals. Additionally, a general overview will be given on distributed reconfigurable mobile terminals in a personal area network (PAN) context. The PAN may include a number of mobile devices, which need to exchange information with each other and with their users; technologies such as Bluetooth, IrDA and WLAN could be employed. Thus, secure data transfer will be needed for properties such as confidentiality, integrity, authentication, and non-repudiation of data. However, the ability of a device to reconfigure raises a number of security issues that will need to be addressed in order to realize the potential of the reconfigurable domain. A highly distributed environment suggests the requirement for security delegation techniques. Additionally, threats increase from malicious software such as viruses, Trojan horses and worms. One can employ secure mobile delegation for securing software upgrades in reconfigurable terminals, from high-level applications and system software, such as ring tones, down to lower-layer baseband modules. With our novel delegation schemes we show that it is possible to maintain end-to-end accountability and at the same time have compact and lightweight cascade characteristics. This has been further enhanced with our innovative security mechanism that can be automatically optimized in various environments These characteristics make our protocols suitable for ubiquitous environment as well as for diverse personalized services and future reconfigurable terminals.

Flexible Delegation Security for Improved Distribution in Ubiquitous Environments

Since one of the services that delegation offers is a more optimised distribution paradigm, recontigurable terminals are envisaged to be able to show how security can negotiate and adapt itself in a flexible way, in favour of performance, without nevertheless compromising fundamental security requirements. So far we observe that protocols that enable cascade delegation and maintain end-to-end accountability among all the involved actors, demonstrate heavy computations or increased network usage and unnecessary redundant complexity. With a novel set of delegation algorithms we show that it is possible to maintain end-to-end accountability and at the same time have compact and lightweight cascade characteristics. This has been further enhanced with an innovative security mechanism that can he automatically optimised in various environments. Due to these attributes, the proposed delegation algorithms will additionally enable recontigurable terminals to perform complicated tasks either when they enter an untrusted PAN or they use a slow communications link. These characteristics make our protocols suitable for ubiquitous environments as well as for diverse personalised services and mobile applications.