Octavian Catrina

During the decade that has elapsed since its standardisation by ISO, the Estelle formal description technique has been successfully applied to the development of various communications protocols. We present in this paper a protocol engineering methodology that has resulted from the use of Estelle in several projects, involving the specification, validation, performance analysis and implementation of real-life, complex protocols. The methodology is based on the support offered by the Estelle Development Toolset (EDT). It gradually evolved, in parallel with the continuous enhancement of EDT, aiming to provide a protocol engineering environment that consistently supports the entire development process. We outline in the paper the principles of the methods and illustrate them with examples of their application to the development of an innovative transport protocol with multicast and multimedia capabilities. .H\ZRUGV Computer aided software engineering tools based on formal description techniques (FDT) can provide essential support for developing communications protocols and distributed systems. Ideally, this support should extend to all the development phases, from requirements capture and design (formal description and validation), to performance evaluation, implementation (automatic code generation) and conformance testing (automatic test generation). The tools gradually mature and become able to cope with industrial applications, but the user still encounters frustrating limitations and contradictions. For example, the design phase produces a simplified or partial formal description, due to limitations of the validation method and/or the FDT, while the automatic implementation requires a complete (yet correct) specification. For complex systems, this gap results in coding the implementation or a large part of it by hand. Also, classical FDT based approach focused on functional properties, neglecting quantitative, real-time properties. A different model is needed for performance analysis (e.g., queuing networks), resulting in substantial additional effort for developing and maintaining it during the design process. However, a trend towards an integrated FDT based methodology can be observed, e.g., in the tools using the standard FDTs Estelle [1] and SDL [2]. An Estelle model of a system is a hierarchy of communicating extended finite state machines , with a rigorous operational semantics. The current standard syntax is similar to that of the Pascal programming language. A graphical syntax has also been proposed [3]. Recent enhancements of the Estelle Development Toolset (EDT) [4] allow a more consistent support of the protocol engineering process, from formal specification to prototype implementation , with performance evaluation in early design phases. Moreover, several case studies have confirmed the applicability of this methodology to real-life, complex protocols. The first case study was dedicated to the Xpress Transport Protocol (XTP) version 4.0 [5]. It consisted of an Estelle specification and validation [6], a performance evaluation by

—A video streaming system with over-the-top delivery has to select the servers that handle the service requests such that the content is delivered with the desired quality and system resources are efficiently used. Server selection can be formulated as a multi-criteria optimization problem, but solving this problem requires dynamic information about system resources. In this paper , we study the performance achieved by service providers that deploy a resource monitoring infrastructure and optimize server selection using a Multi-Criteria Decision Algorithm (MCDA), and the performance achieved by lightweight service providers, using only static information and simpler selection methods. We implemented these methods in a simulator and compared their performance. The results show that MCDA offers important performance gains, justifying the costs of resource monitoring. Moreover, they motivate the search for server selection methods that could achieve similar performance with lower costs, by involving the clients in the selection process, using MCDA.

Secure Multiparty Computation (SMC) protocols enable a group of mutually distrustful parties to perform a joint computation with private inputs. Novel e-commerce applications have emerged that could benefit from strong privacy protection, e.g., benchmarking, auctions, and collaborative supply chain management and planning. However, the uptake of SMC in these applications is still rare. We argue that this is due to poor performance, func-tionality, and scalability, as well as architectures that do not meet the needs of e-commerce applications. This paper explores SMC approaches and research directions, aiming at providing better support for e-commerce applications.

More effective algorithms and improved computing support have extended the applications that can be effectively tackled by validation methods based on simulation (state space exploration). However, the huge state spaces and complex functionality of most applications remain major problems. We present a validation method that uses guided simulation for a functional decomposition of the system's behav- iour. Essential aspects of

Abstract The SecureSCM project demonstrates the practical applicability of secure multiparty computation to online business collaboration. A prototype supply-chain management system protects the confidentiality of private data while rapidly adapting to changing business needs.