A new system engineering methodology coupling formal specification and performance evaluation

The situation of telecommunications systems is rapidly evolving towards a state characterized by the presence of a multitude of services integrated in a single network structure. In order to ease their integration, it is important to provide an unambiguous description of the organization, of the functionality, and of the relationships existing among services. Since it is not possible to completely foresee the situation of services in the future, the description should be modular, so that the task of adding new services to an existing environment is simplified. Formal description techniques are languages designed to handle such descriptions. Their goal is to produce correct and unambiguous specifications, understanding and modeling the system and the domain within which it operates. Their input is a set of required statements and a conceptual overview of the system. Their output is a formal representation that captures the functional behavior. On the other hand, the throughput of physical networks is constantly growing, reaching the order of Gbit/s. In the meantime, services needing high throughput, like multimedia conferencing systems are being designed, creating a need for flexible, high performance communication systems. An important feature of new high speed services is their increased need for guarantees. Therefore, the use of powerful performance modeling techniques becomes of prime importance. Their goal is to obtain some notion of how the system will perform under a given set of conditions. Performance evaluation theorists have long been using system specifications to make a heuristic model of the system and then an analysis of the model. When system specifications exist, the question arises whether a more direct path to performance analysis can be found. Our scope is to provide a methodology that fully and consistently integrates formal specification and performance evaluation. A problem is that many of the bottlenecks and impediments to smooth data flow have to do with implementation issues not directly dealt within the system specification itself. Therefore, prior to generating a performance model, the formal specification should be enhanced with the relevant non-functional information. It is essential to assure a smooth specification of the non-functional information. Thus, it is necessary to consistently add this information to the formal specification. Besides, the extended formal method should focus on conserving the semantics of the original one, and on providing a coherent extension of the semantics and syntax for the new concepts. Since all relevant required information is integrated within the formal extended representation, we provide a mapping technique that translates the extended formal representation into a performance modeling conserving the properties of the formal model. In parallel to the development of a performance model, the formal model can be validated and verified, and their implementation can be tested for conformance towards the original formal model. Finally, the performance modelling is implemented in a programming language, and then simulated. The results from simulation can be reused as inputs for the optimization of the formal specification (functional optimization) or the extended formal model (design optimization). To sum up, the goal of this work is to: Define extensions to current formal methods that allow to enhance the formal specification with performance modeling related information. Develop a method to translate the extended formal specification into a performance modeling. Develop rules and guidelines to automatically implement the performance modeling for the purpose of a performance evaluation (we use the commercial tool Opnet). Develop a consistent and coherent methodology for the integration of performance modeling and formal specification.

Due to the development and evolution in Cognitive Radio Networks (CRNs), the performance of Transmission Control Protocol (TCP) over CRN has become a crucial factor. TCP ensures the reliable end-to-end delivery of data, which is very important for the quality of service (QoS) requirements. TCP performance is severely affected by channel switching and channel availability in CRNs. The frequent occurrence of such events is due to CRNs nature which unnecessarily reduces the transmission rate which results in degrading the overall performance. In this paper, the authors investigate the limitations of using TCP NewReno (i.e., standard TCP) over CRNs, and further propose a cross-layer-design protocol based on an interaction between transport layer and lower layers to improve TCP performance over CRNs. The design is called Cross-Layer Design for TCP (TCP-CLD). It primarily aims at improving the TCP performance over CRNs via controlling and adapting a few selected TCP parameters. Specifically, the authors propose freezing the data transmission and re-transmission timeout (RTO) of TCP during the time of channel switching and channel unavailability. In addition, the authors update the size of congestion window (cwnd) of TCP based on the bandwidth and buffer size of relay nodes. Moreover, in the case of channel switching, the authors update the Round Trip Time (RTT) of TCP based on the new route delay. Simulation experiments have been conducted using ns-2 network simulator tool whereas results show that the proposed design achieves a significant performance improvement compared with the standard TCP NewReno protocol and the other known protocol, namely, TCP-CRAHN.

A class-based scheme for E-commerce web servers: Formal specification and performance evaluation

This paper describes formal verification and quantitative performance evaluation for validating of query pattern-based relational schema-to-XML Schema translation (QP-T) algorithm. Many translation algorithms such as FT, NeT, CoT, ConvRel, and VP-T have been introduced on structural and/or semantic aspect for exact and effective translation. However, conventional algorithms consider only explicit referential integrity specified by relational schema or limitations regarding on reflection of implicit referential integrity information. It causes several problems such as incorrect translation, abnormal relational model transition, and so on. The QP-T algorithm analyzes query pattern and extract implicit referential integrities by interrelationship of equi-join in user queries. The QP-T algorithm can make up for weak points of the VP-T algorithm and create more exact XML Schema as a result by using with VP-T algorithm together.KeywordsLoss RatioDatabase SchemaFormal VerificationSemantic DescriptionQuery PatternThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

현재 인터넷에서는 객체를 전송하기 위해 HTTP over TCP가 사용된다. SCTP는 TCP의 문제점을 보완하기 위해 제안된 프로토콜로 개별적인 스트림을 이용하여 데이터를 전송하므로 웹 객체의 평균 응답 시간을 감소시킬 수 있다. 본 논문에서는 HTTP over SCTP의 평균 응답 시간을 추정하는 해석적 모델을 개발함으로써 TCP에 대한 SCTP의 효과를 추정하고자 한다. TCP 지연을 구하기 위한 기존의 해석적 모델이 주로 유선 환경을 가정한데 비해, 본 연구에서 제안하는 모델은 다중 패킷 손실이 발생하고, 빠른 재전송이 가능하지 않은 무선 환경을 가정한다. 추정된 평균 응답 시간은 실제 웹 응용을 개발할 때, 종단 사용자의 서비스 품질을 만족시키기 위한 사전 벤치마크로 사용될 수 있다. 추정 모델의 타당성을 검증하기 위해 테스트베드 상에서 성능 실험을 수행한 결과, 모델과 실험결과의 차이가 평균 6% 이내로 매우 작으며, 동시에 HTTP over SCTP의 평균 전송 시간이 HTTP over TCP의 평균 전송 시간보다 작은 것으로 확인되었다. Hyper text transfer protocol (HTTP) over transmission control protocol (TCP) is currently used to transfer objects in the Internet. Stream control transmission protocol (SCTP), an alternative to TCP, which allows for independent delivery among streams, and can thus reduce the mean response delay of web object. We present an analytical model to find the mean response delay for HTTP over SCTP, therefore, estimate the effectiveness of SCTP over TCP. Typical TCP delay models assume the wired environment. On the contrary, the proposed model in this paper assumes the multiple packet losses and wireless environment where fast retransmission is not possible due to small window. The estimated mean response time can be used the benchmark to meet quality of service (QoS) at end-user. We validate the accuracy of our model using experiments. It is shown that the differences between the results from model and those from experimental are very small below 6 % on average. We also find that the mean response delay for HTTP over SCTP is less than that for HTTP over TCP.

Power Line Communications (PLC) is regarded as the promising home networking technology for smart grid application since the PLC technology enables data transmission via the existing power line. The cooperation between PLC and Wireless Local Area Network (WLAN) will be an effective hybrid solution for Home Area Networks (HANs). In this paper, we consider that Transmission Control Protocol (TCP) packets are transmitting in heterogenous communications network based on PLC and WLAN. The existing TCP congestion control has low effectiveness due to the error-prone power line channel. Therefore, we propose an adaptive rate control to improve TCP performance in the hybrid PLC/WLAN HANs. We exploit the communications mechanism of WLAN to improve the PLC link utilization. The methodology of Heuristic Dynamic Programming (HDP) is employed to obtain the optimal rate policy. The bottleneck link capacity is estimated by neural network training. The sending rate is adapted according to the long-term quality of service (QoS) of applications. Simulation results illustrate that the proposed rate control effectively filters out the negative impact from the instantaneous impulse noise in PLC channel and outperforms the existing TCP.

Despite offering reliability against dropped and reordered packets, the widely adopted Transmission Control Protocol (TCP) provides nearly no recovery options for longterm network outages. When the network fails, developers must rollback the application to some coherent state on their own, using error-prone solutions. Overcoming this limitation is, therefore, a deeply investigated and challenging problem. Existing solutions range from transport-layer to application-layer protocols, including additions to TCP, usually transparent to the application. None of these solutions is perfect, because they all impact TCP's simplicity, performance or ubiquity, if not all. To avoid these shortcomings, we contain TCP connection crashes inside a single session layer exposed as a sockets interface. Based on this interface, we create a blocking and a non-blocking fault-tolerant design pattern. We explore the blocking design in an open source File Transfer Protocol (FTP) server and perform a thorough evaluation of performance, complexity and overhead of both designs. Our results show that using one of the patterns to tolerate TCP connection crashes, in new or existing applications, involves a very limited effort and negligible penalties.

: The goal of our research is to provide a framework for constructing complex, distributed systems that can autonomously adapt to their environment. There were three key elements to this framework. The first element was a metal-model for developing distributed, adaptive systems based on organization theory - the Organization Model for Adaptive Computational Systems (OMACS). OMACS defines the required components for an adaptive organization - agents, goals, roles, and capabilities - as well as an approach for computing the best organization of those components. The second framework element created was a the Goal Model for Adaptive Systems, which handles the runtime goals based on precedence between goals as well as runtime instantiation of new goals based on events that occur in the environment. The final part of the framework developed was a software engineering methodology for designing distributed, adaptive systems using a dynamic goal model. The Organization-based Multiagent Systems Engineering (O-MaSE) methodology is based on the Multiagent Systems Engineering methodology and incorporates all OMACS components.

The recently published Air Force Systems Command Manual 375-5 (AFSCM 375-5), System Engineering Management Procedures, prescribes the management policies and procedures to be followed in the establishment of requirements for, and in the design, development, test, operation, and maintenance of future Air Force systems. The life cycle of systems requiring AFSCM 375-5 implementation is described and the prescribed system engineering management process and significant documentation tools are discussed in detail. In addition, possible implementation problems and solutions associated with the application of AFSCM 375-5 are discussed.

A crucial component of quality management is assessment of personnel competency. Obtaining reliable results from the testing personnel in the andrology laboratory, often referred to as “andrologists,” requires attention to hiring, training, and performance evaluation. The perfect fit for an andrology laboratory may not be the most experienced individual but relies on character traits, including teamwork, integrity, confidence, and analytical thinking. Training the new employee begins with instructions covering the laboratory’s policies, chain of command, safety, compliance with regulations, and reliance on standard operating procedures. Approval of the technician to perform patient testing requires observation of trained andrologists, side-by-side testing, practice with semen, and testing under close supervision. Benchmarks of successful training are important in this process. Continuing education throughout a technician’s career will ensure that the knowledge base in the laboratory keeps up with modern methodology. Evaluation of personnel competence begins during training and is continuous throughout the andrologist’s career. Quality control (QC) of technical performance includes intra-laboratory evaluation of inter-technician variation, interlaboratory evaluation to ensure uniform results, and formal performance evaluation with goals for improved performance. This chapter discusses these aspects of personnel competency assessment, giving examples of personnel forms and QC results.

A Mobile Ad Hoc Network represents a system of wireless mobile nodes that can freely and dynamically selforganize into arbitrary and temporary network topologies, allowing people and devices to seamlessly communicate without any pre-existing communication architecture. The growth of real time multimedia application in such environments, has drawn a lot of attention to wireless networks that support quality of service (QoS). In this work, the QoS metrics, delay and link life time (LLT) of the path are dynamically calculated. Based on these values the routing decisions are made. Here the multipath routing protocol is taken as the base protocol. The proposed algorithm finds the multiple QoS routes only, based on the QoS metrics and stores only those paths in the routing table. The route is selected based on the integrated QoS metric and is used to transmit the data. The base protocol used is multipath AODV(Ad Hoc On demand Distance Vector ) routing protocol. The proposed protocol may take extra time during route discovery process to compute the additional QoS parameters, but this time is compensated by having only QoS paths for data transmission. A few patents on the QoS Routing for MANETS have been reviewed.The simulator NS-2.34 is used to simulate and compare the performance of the protocols in terms of the QoS metrics such as end-to-end delay, PDR in the MANET. Keywords: Mobile Ad Hoc Network (MANET), Quality of Service (QoS), Destination Sequence Distance Vector (DSDV), Dynamic Source Routing (DSR), Ad Hoc On demand Distance Vector (AODV), LLT (Link Life Time), RLT (Route Life Time), PLTR (Percentage Life Time Ratio), TCP (Transmission Control Protocol), CBR (Constant Bit Rate), PDR (Packet Delivery Ratio).

Wireless internet has become popular in recent years due to the tremendous growth in the number of mobile computing devices and high demand for continuous network connectivity regardless of physical locations. In this paper, we investigate the effects of routing protocols on the performance of Transmission Control Protocol (TCP) variants in multi-hop wireless networks. Through simulations we study the effects of Destination Sequenced Distance Vector (DSDV), Optimized Link State Routing (OLSR), Ad hoc On demand Distance Vector (AODV) and Dynamic Source Routing (DSR) routing protocols on TCP Tahoe, TCP Reno, TCP Newreno, TCP with Selective Acknowledgment (SACK) option and TCP Vegas. The simulations are carried out for static as well as mobile nodes. The performance metric used is throughput. Another metric, expected throughput is used for the comparison of throughput when nodes are mobile.

Minimum TCP throughput guarantee on minimum rate guaranteed networks

LTE standard provides different Quality of Service (QoS) options which enable to provide multiple services to the User Equipment (UE). Design of scheduling algorithm for Transmission Control protocol (TCP) based traffic is challenging in wireless networks. Many papers have been developed to improve the throughput of TCP traffic. In this work, a novel and practically feasible scheduling algorithm is proposed to handle the TCP traffic in order to improve the overall LTE cell and UE throughput. An uplink grant is provided at the time of scheduling Downlink (DL) TCP traffic for acknowledgement transfer which minimizes TCP throughput fluctuations which improves cell and per UE throughput. The amount of advanced uplink grant can be computed using Kalman filter algorithm by considering real time reported parameters as per LTE standard. The proposed algorithm is implemented in small cell platform and real time results are generated. It shows that significant gain is achieved in throughput under specific traffic conditions.

The Air Traffic Control industry is being increasingly exposed to rising levels of risk, as criminals and cyber‐attackers look to exploit system vulnerabilities. Air Navigation Service Providers become more demanding regarding cybersecurity concerns in the products they acquire. Consequently, systems engineers need to consider cyber security concerns early in their system's development life cycle. Model‐Based Systems Engineering methodologies are widely used to manage complex engineering projects in terms of system requirements, design, analysis, verification, and validation activities, leaving cyber security aspects aside. This paper presents a conceptual solution of a model‐based security method that aims to enable systems engineers to perform threat modeling analysis of cyber‐physical systems early and incorporate mitigation strategies into the system design, thereby reducing the cyber‐physical system's overall security‐related risks. Based on a real‐life case study the method will be validated later during execution period from Jan. – May 2022.