Improving Requirements Specification for Communication Services with Formalised Use Case Models

The challenging task of requirements specification for communication services has not been sufficiently addressed to date. The complexity of communication systems requires a formal approach to requirements capture and analysis, however at the same time the industry does not take well to convoluted formalisms. We suggest improving requirements specification by enhancing the approach that is most popular at the moment - use case modelling. We amend traditional use case models with a formal structure and semantics to make them suitable for automated verification. The enhanced use case modelling technique that we propose is called Susan (”S”ymbolic ”us”e case ”an”alysis) and it facilitates verification of use case models using symbolic model checking. We also developed a software tool called SusanX to construct, manipulate and analyse Susan models. The analysis feature of the tool is implemented using the NuSMV model checker. A number of generic properties for verification are built into SusanX, and the tool additionally allows the user to construct model-specific properties

Improving Requirements Specification: Verification of Use Case Models with Susan

Inadequate requirements specification is one of the main causes of software development project failure today. A major problem is the lack of processes, techniques and automated tool support available for specifying system requirements. We suggest a way to improve requirements specification methodology by enhancing the approach that is most popular at the moment - use case modelling. Despite their popularity, use case models are not formal enough for automated analysis. We amend traditional use case models with a formal structure and semantics to make them suitable for automated verification. The enhanced use case modeling technique that we propose is called Susan (”S”ymbolic ”us”e case ”an”alysis) and it facilitates verification of use case models using symbolic model checking. We also developed a software tool called SusanX to construct, manipulate and analyse Susan models. The analysis feature of the tool is implemented using the NuSMV model checker. A number of generic properties for verification are built into SusanX, and the tool additionally allows the user to construct model-specific properties

Models of Hybrid Wireless Networks with Realistic Workloads

More and more the integration of WiFi and WiMaX wireless networks seem to be the favorite metropolitan area networking option for the future. Some authors refer to these as hybrid wireless networks (HWN). Call admission control in HWN, the efficiency of routing protocols and so on, depend on the QoS or performance of the network. In order to predict the performance of these networks one needs to build a prototype or model them. Simulation models are clearly an option, but simulations become complex, are hard to validate and require much processor time when the network becomes large. In this paper we advocate a hierarchy of models build upon an analytic multiclass queueing network model. We show the results of comparing such a network with simulations of the same network and using inter arrival time and packet distributions of measured Internet traffic. While trends are the same between the simulation and analytic model results, the absolute values are not

A Tutorial on RAID Storage Systems

RAID storage systems have been in use since the early 1990's. Recently, however, as the demand for huge amounts of on-line storage has increased, RAID has once again come into focus. This report reviews the history of RAID, as well as where and how RAID systems fit in the storage hierarchy of an Enterprize Computing System (EIS). We describe the known RAID configurations and the advantages and disadvantages of each. Since the focus of our research is on the performance of RAID systems we devote a section to the various factors which affect RAID performance. Modelling RAID systems for their performance analysis is the topic of the next section and we report on the issues as well as briefly describe one simulator, RAIDframe, which has been developed. We conclude with section which describes the current open research questions in the area

Analysis of Structured Use Case Models through Model Checking

Inadequate requirements specification remains to be one of the predominant causes of software development project failure today. This is mainly due to the lack of suitable processes, techniques and automated tool support available for specifying and analysing system requirements. In this paper we suggest a way to improve the approach to requirements specification that is the most popular at the moment - use case modelling. Despite their popularity, use case models are not adequate for creating comprehensive and precise requirements specifications. We amend the traditional use case metamodel such that more formal and structured models can be built. Further, we define several analysis schemes for these structured use case models that assist in discovering inconsistencies and other errors in the models. These analysis schemes are automated in a tool that we developed called the Structured Use case Model Analyser (SUM Analyser). The SUM Analyser provides an accessible interface that allows the user to construct use case models, configure and execute several analysis options and view the produced results. The existing NuSMV model checker is used to perform the actual verification tasks for the analysis. To facilitate this, the SUM Analyser transforms use case models to NuSMV programs and also interprets the produced results so that they can be understood by the user

Delay Analysis of Downlink IP Traffic on UMTS Mobile Networks

Since wireless networks which can carry high bit rates have become ubiquitous, mobile computing is no longer just spoken about. Mobile computing always implies access through a wireless network to an IP network such as the Internet. In order to understand the performance of such links, we propose an analytic model for the down link delay of IP traffic between the Mobile Gateway Server and the End User in a UMTS mobile network. Traffic arriving at the Gateway Server is considered to be bursty in nature and we use a Batch Markovian Arrival Process (BMAP) to model this arrival process. We model the wireless link itself as a modified multi-state Gilbert–Elliot Markov model which takes into account the number of interfering users and whether the channel experiences Ricean fading or not for what we consider a typical indoor, IP-centric environment. We also account in both the analytical model and the simulation for the Forward Error Correction provided by Turbo coding in UMTS to establish realistic packet retransmission rates. Finally we calibrate and verify the correctness of the model with a discrete event simula

A Methodology for Analyzing Power Consumption in Wireless Communication Systems

We propose a methodology that allows software protocol implementors a means of analyzing power consumptions in wireless communication systems. The energy intensive nature of wireless communication has spurred much concern over how best systems can make the most use of this nonrenewable energy source. The methodology involves describing the logical flow of protocol data units through the protocol layers based on their formal specification. Here after, the state diagrams of the protocol layers are derived from this logical description. These diagrams provide the schema for the continuous-time Markov chains that enable the capturing of the protocol layer's behaviour. Markov Reward Models are then specified by defining the Markov chains that allow for the modelling of power consumption as a reward. Modelling power consumption this way allows for the investigation of the power factor, power level analysis, and power consumption comparison of the radio interface protocol layers

Towards Model-Based Communication Protocol Performability Analysis with UML 2.0

In this paper we propose a methodology for the modelling, verification and performance evaluation of communication components of distributed application building software. The methodology is centered upon model-driven development using a subset of UML 2.0 diagrams. It is supported by the proSPEX model processing tool which translates UML 2.0 specifications into executable simulation models. In our proSPEX discussion we focus on the translation from a UML 2.0 model to a simulation model. The model-based development of communication components of wireless middleware solutions is discussed as a motivational example

Wireless Standards and Mesh Networks.

On March 13th 1980, the Computer Society of the Institute of Electronics and Electrical Engineering (IEEE) approved project 802. IEEE 802 is led by the LAN/MAN Standards Committee(LMSC). Until today, 22 Working Groups (WGs) mainly define standards for the lowest two layers of the ISO/OSI reference model in the 802. For wireless communication, 802.11 WG defines the Wireless Local Area Network (WLAN), 802.15 WG defines the Wireless Personal Area Network (WPAN), and 802.16 WG defines the Wireless Metropolitan Area Network (WMAN) standard. With Multiple Input/Multiple Output (MIMO), Ultrawideband (UWB) and sensitive Modulation and Coding Schemes (MCSs), the latest developments in the IEEE 802 standards enable data rates beyond 500Mbps for new applications of wireless communication. Similar to preceding wireless technologies, data rate slows down by increase in distance of the communication entities. However, demands for new applications emerge that need high data rates regardless of distance. To overcome the link speed limitation, dense deployment of wireless networks is needed1. Wireless Mesh Networks (WMNs) help to overcome current dependencies of wireless communication systems on wired backbones by enabling cost-effective and rapid deployment for a new generation of wireless services

Using UML Models for the Performance Analysis of Network Systems

The automated functional and performance analysis of communication systems specified with some Formal Description Technique has long been the goal of telecommunication engineers. In the past SDL and Petri nets have been the most popular FDTs for the purpose. With the growth in popularity of UML the most obvious question to ask is whether one can translate one or more UML diagrams describing a system to a performance model. Until the advent of UML 2.0, that has been an impossible task since the semantics were not clear. Even though the UML semantics is still not clear for the purpose, with UML 2.0 now released and using ITU recommendation Z.109, we describe in this paper a methodology and tool called proSPEX, for the design and performance analysis of communication protocols specified with UML