Maryam Kamali

Quantitative Analysis of AODV and its Variants on Dynamic Topologies using Statistical Model Checking

Wireless Mesh Networks (WMNs) are self-organising ad-hoc networks that support broadband communication. Due to changes in the topology, route discovery and maintenance play a crucial role in the reliability and the performance of such networks. Formal analysis of WMNs using exhaustive model checking techniques is often not feasible: network size (up to hundreds of nodes) and topology changes yield state-space explosion. Statistical Model Checking, however, can overcome this problem and allows a quantitative analysis.

Topology-Based mobility models for wireless networks

The performance and reliability of wireless network protocols heavily depend on the network and its environment. In wireless networks node mobility can affect the overall performance up to a point where, e.g. route discovery and route establishment fail. As a consequence any formal technique for performance analysis of wireless network protocols should take node mobility into account. In this paper we propose a topology-based mobility model, that abstracts from physical behaviour, and models mobility as probabilistic changes in the topology. We demonstrate how this model can be instantiated to cover the main aspects of the random walk and the random waypoint mobility model. The model is not a stand-alone model, but intended to be used in combination with protocol models. We illustrate this by two application examples: first we show a brief analysis of the Ad-hoc On demand Distance Vector (AODV) routing protocol, and second we combine the mobility model with the Lightweight Medium Access Control (LMAC).

Formal Modeling of Multicast Communication in 3D NoCs

A reliable approach to designing systems is by applying formal methods, based on logics and set theory. In formal methods refinement based, we develop the system models stepwise, from an abstract level to a concrete one by gradually adding details. Each detail-adding level is proved to still validate the properties of the more abstract level. Due to the high complexity and the high reliability requirements of 3D NoCs, formal methods provide promising solutions for modeling and verifying their communication schemes. In this paper, we present a general model for specifying the 3D NoC multicast communication scheme. We then refine our model to two communication schemes, : unicast and multicast, via the XYZ routing algorithm in order to put forward the correct-by-construction concrete models.

Formal development of wireless sensor-actor networks

Wireless sensor-actor networks are a recent development of wireless networks where both ordinary sensor nodes and more sophisticated and powerful nodes, called actors, are present. In this paper we introduce several, increasingly more detailed, formal models for this type of wireless networks. These models formalise a recently introduced algorithm for recovering actor-actor coordination links via the existing sensor infrastructure. We prove via refinement that this recovery is correct and that it terminates in a finite number of steps. In addition, we propose a generalisation of our formal development strategy, which can be reused in the context of a wider class of networks. We elaborate our models within the Event-B formalism, while our proofs are carried out using the RODIN platform - an integrated development framework for Event-B.

Formal analysis of proactive, distributed routing

As (network) software is such an omnipresent component of contemporary mission-critical systems, formal analysis is required to provide the necessary certification or at least formal assurances for these systems. In this paper we focus on modelling and analysing the Optimised Link State Routing (OLSR) protocol, a distributed, proactive routing protocol. It is recognised as one of the standard ad-hoc routing protocols for Wireless Mesh Networks (WMNs). WMNs are instrumental in critical systems, such as emergency response networks and smart electrical grids. We use the model checker Uppaal for analysing safety properties of OLSR as well as to point out a case of OLSR malfunctioning.

Self-Recovering Sensor-Actor Networks

Wireless sensor-actor networks are a recent development of wireless networks where both ordinary sensor nodes and more sophisticated and powerful nodes, called actors, are present. In this paper we formalize a recently introduced algorithm that recovers failed actor communication links via the existing sensor infrastructure. We prove via refinement that the recovery is terminating in a finite number of steps and is distributed, thus self-performed by the actors. Most importantly, we prove that the recovery can be done at different levels, via different types of links, such as direct actor links or indirect links between the actors, in the latter case reusing the wireless infrastructure of sensors. This leads to identifying coordination classes e.g., for delegating the most security sensitive coordination to the direct actor-actor coordination links, the least real-time constrained coordination to indirect links, and the safety critical coordination to both direct actor links and indirect sensor paths between actors. Our formalization is done using the theorem prover in the RODIN platform.

A distributed recovery mechanism for actor-actor connectivity in wireless sensor actor networks

Wireless sensor actor networks (WSANs) consist of a number of sensor nodes and actor nodes in a distributed network. Sensor nodes collect data from environment and report them to actor nodes or to a sink node. Actor nodes coordinate to take decisions and accordingly take suitable actions. To coordinate, actor nodes must communicate with each other through their network connections. Therefore, actor-actor connectivity is vital to coordination. A node failure may lead to network partitioning. This paper proposes a distributed mechanism for recovering the connectivity failures among actors in their partitioned network. Sensor nodes are used to temporarily and rapidly re-establish actor-actor connectivity long before this connectivity is permanently re-established through movements of some actors. It is shown that the proposed mechanism increases the availability of connectivity while the actorspsila connectivity undergoes repair by actor movement. Simulation results also show a comparatively lower time to repair for our approach.

Recharging Sensor Nodes Using Implicit Actor Coordination in Wireless Sensor Actor Networks

Wireless sensor actor networks are composed of sensor and actor nodes wherein sensor nodes outnumber resource-rich actor nodes. Sensor nodes gather information and send them to a central node (sink) and/or to actors for proper actions. The short lifetime of energy-constrained sensor nodes can endanger the proper operation of the whole network when they run out of power and partition the network. Energy harvesting as well as minimizing sensor energy consumption had already been studied. We propose a different approach for recharging sensor nodes by mobile actor nodes that use only local information. Sensor nodes send their energy status along with their sensed information to actors in their coverage. Based on this energy information, actors coordinate implicitly to decide on the timings and the ordering of recharges of low energy sensor nodes. Coordination between actors is achieved by swarm intelligence and the replenishment continues during local learning of actor nodes. The number of actors required to keep up such networks is identified through simulation using VisualSense. It is shown that defining the appropriate number of actor nodes is critical to the success of recharging strategies in prolonging the network lifetime.

A distributed design of a network recovery algorithm

The increase in design complexity emphasises the relevance of formal verification techniques for both software and hardware. Formal methods with their mathematical-based modelling can provide proofs of various properties for the designs, thus ensuring a certain degree of complexity control and enhancing the system confidence. There are numerous formal modelling and verification techniques employed in designing complex systems. Typically, they either prove or disprove the correctness of the particular specifications of a system’s algorithms with respect to certain initial requirements. The Event-B formal method has been recently extended to address the gap between specification and implementation, via the so-called modularisation extension. In this paper, we present a modularisation-based derivation of a distributed design for a network recovery algorithm, based on the refinement technique of Event-B. We thus contribute to enhancing the reliability and availability of network designs.

Agent-based autonomous systems and abstraction engines: Theory meets practice

We report on experiences in the development of hybrid autonomous systems where high-level decisions are made by a rational agent. This rational agent interacts with other sub-systems via an abstraction engine. We describe three systems we have developed using the EASS BDI agent programming language and framework which supports this architecture. As a result of these experiences we recommend changes to the theoretical operational semantics that underpins the EASS framework and present a fourth implementation using the new semantics.