Performance evaluation of TCP-based applications over DVB-RCS DAMA schemes

Transmission Control Protocol (TCP) performance over Digital Video Broadcasting-Return Channel via Satellite (DVB-RCS) standard is greatly affected by the total delay, which is mainly clue to two components, propagation delay and access delay. Both are significant because they are dependent oil the long propagation path of the satellite link. I-lie former is intrinsic and due to radio wave propagation over the satellite channel for both TCP packets and acknowledgements. It is regulated by the control loop that governs TCP. The latter is due to the control loop that governs the demand assignment Multiple access (DAMA) signalling exchange between satellite terminals and the network control center. necessary to manage return link resources. DAMA is adopted in DVB-RCS standard to achieve flexible and efficient use of the shared resources. Therefore, performance of TCP over DVB-RCS may degrade due to the exploitation of two nested control loops also depending oil both file selected DAMA algorithm and the traffic profile. This paper analyses the impact of basic DAMA implementation oil TCP-based applications over a DVB-RCS link for a large Set Of study Cases. To provide a detailed overview of TCP performance in DVB-RCS environment, the analysis includes both theoretical approach and simulation campaign. Copyright (C) 2009 John Wiley & Sons, Ltd

Cross-layer architecture for a satellite-Wi-Fi efficient handover

To achieve fully mobile communications, considering different environments and modern service requirements, a multiple-segment architecture is the most suitable to guarantee service continuity with acceptable performance. Handover (HO) procedures can be invoked either out of necessity (if the current network connection is going off) or to improve performance (if different bandwidth or quality of service is required). In this scenario, to provide uninterrupted communication services, efficient intersegment HO capability must be implemented. The architecture considered includes a satellite segment and a number of Wi-Fi hot spots. A mobile node (MN) can switch from a segment to other exploiting services of mobile Internet protocol (MIP). This architecture introduces great flexibility and ensures capillary coverage; it also strongly affects Transmission Control Protocol (TCP)-based application performance. To efficiently face HO consequences, particularly when the TCP runs as a transport protocol, an innovative protocol architecture based on cross-layer (CL) exchange of information is proposed. Analyses of TCP dynamics during HOs and the performance improvement introduced with the proposed CL architecture, evaluated through the network simulator Ns-2, are presented

A TCP Driven CAC scheme: efficient resource utilization in a leaky HAP-satellite integrated scenario

An integrated high altitude platform (HAP)-satellite communication system appears to be very suitable for a large set of scenarios including emergency situations, exceptional events, etc. In fact, the satellite capability to provide a broadband and ubiquitous access can be enhanced by the deployment of HAP that allows the use of low-power consuming, cost-efficient, and portable terminals. To obtain an optimum utilization of radio resource, without renouncing to QoS satisfaction, a suitable call admission control scheme must be implemented. Nevertheless, transmission control protocol (TCP) behavior, mainly affected by the high latency and shadowing events, can impact call admission control (CAC) performance. Therefore, it would be desirable that the CAC scheme takes into account also the TCP congestion window real evolution. We present an innovative CAC scheme that uses TCP statistics as one of its inputs and is able to manage different classes of users. Results show that CAC performance is significantly improved by introducing TCP statistics about network congestion as an input parameter

CAC-TCP cross-layer interaction in a HAPS-satellite integrated scenario

The integration of a satellite system with a HAPS segment appears very suitable to provide communication services, including Internet access, for a large set of applications. In fact, the-satellite capability to provide wide coverage and broadband access can be enhanced by the use of cost-effective, mobile/portable and low-power consuming user terminals, when HAPS acts as an intermediate repeater. Moreover, also TCP-based applications, which suffer from long latency introduced by the satellite link and in general by errors, can get benefits in terms of end-to-end performance. In this frame, this paper deals with the introduction, on board the HAPS, of an efficient CAC scheme in order to guarantee an optimal utilization of the precious radio resources. In particular, we propose an innovative TCP driven CAC algorithm, which shall take into account not only the QoS requirements, but also TCP statistics obtained through a proxy installed on the HAPS. Results show that the overall system performance in terms of both average throughput and blocking probability is significantly improved

A inclusão dos alunos com deficiência no contexto escolar

Orientadora : Tainá Ribas MéloMonografia (especialização) - Universidade Federal do Paraná, Setor Litoral, Curso de Especialização em Especialista em Gênero e Diversidade na EscolaInclui referênciasResumo : O presente artigo tem como problemática de investigação verificar se uma determinada escola inserida no município de Itajaí realiza a inclusão dos/as alunos/as com deficiência no contexto dos primeiros anos do ensino fundamental. O objetivo é investigar o processo de inclusão partindo das questões relativas à acessibilidade oferecida aos/as alunos/as com deficiência bem como o processo de ensino aprendizagem a que fazem parte. A metodologia do estudo é de caráter quali- quantitativo sendo a investigação realizada através de observações das atividades escolares e da aplicação de questionário às professoras e agentes de apoio em educação especial. O trabalho teve apoio de autores como Mantoan (1997), Manzini (2004), a Lei de Diretrizes e Bases (1996), os marcos político–legais da Educação Especial (2010) entre outros. A partir destes estudos e o resultado da pesquisa pode-se concluir que no contexto da escola pesquisada a inclusão dos alunos/as com deficiência é uma meta a ser alcançada principalmente no que diz respeito à acessibilidade no entorno e no ambiente escolar, nas práticas pedagógicas adotadas pelos docentes e nas atividades dirigidas em espaços de uso comum. Para isso propostas de ações serão sugeridas partindo dos momentos de formação continuada, à sistematização, implementação e adaptação dos recursos pedagógicos no contexto educacional bem como a parceria com professores/as e agentes de apoio em educação especial na busca de um sistema educacional inclusiv

A cross-layer architecture for satellite network security: CL-IPsec

Cross-layer architectures (CLAs) are proposed to improve performance in networks where physical layer impairments are unpredictable and provision of security services may be challenging, as in satellite networks. This paper proposes an extension to the IPsec protocol, named Cross-Layer IPsec (CL-IPsec), able to provide authentication and integrity services through a cross-layer architecture when the adopted protocol is UDP-Lite. This is suitable for multicast applications that are cost-effectively provided by satellite systems. A satellite emulation platform has been used to validate the CL-IPsec implementation and to evaluate the performance improvement derived from the proposed CLA. © 2008 IEEE

Performance Evaluation of a Satellite Communication-based MEC architecture for IoT applications

New scenarios and use cases are raising following the birth of the fifth generation of mobile communications. The Internet of Things (IoT) is one of the main use cases which are growing, leading to a massive amount of data that need to be exchanged throughout the Internet. Satellite communication networks are essential in remote and isolated environments and can support fully connected environments by offloading the terrestrial infrastructure concerning delay–tolerant traffic flows. However, satellite network resources are limited and expensive, so they need to be carefully used in order to avoid waste and satisfy the required user performance. The multi-access edge computing (MEC) concept can be exploited in this context to allow data preprocessing at the edge, i.e., close to the users, so reducing the amount of data that has to traverse the backhaul satellite link and, in some cases, reducing data delivery times. This article analyses the performance of a satellite architecture in the IoT framework highlighting the advantages brought by MEC, also including data aggregation and compression techniques

Network layer security: Design for a cross layer architecture

Traditional modular layering schemes have served a major part in the development of a variety of protocols. However, as the physical layer impairments become more unpredictable, a cross layer design (CLD) which is dynamic in nature provides better performance. CLD introduces new challenges in protocol design as well as in the area of security. Using numerical analysis, we show that a link layer design employing header compression and cross layer signalling to protect protocol headers can limit packet discarding. This paper also reviews the IPsec protocol and describes how IPsec can be modified for cross layer architecture. © 2007 IEEE

Betaine-The dark knight of the brain

The role of betaine in the liver and kidney has been well documented, even from the cellular and molecular point of view. Despite literature reporting positive effects of betaine supplementation in Alzheimer's, Parkinson's and schizophrenia, the role and function of betaine in the brain are little studied and reviewed. Beneficial effects of betaine in neurodegeneration, excitatory and inhibitory imbalance and against oxidative stress in the central nervous system (CNS) have been collected and analysed to understand the main role of betaine in the brain. There are many 'dark' aspects needed to complete the picture. The understanding of how this osmolyte is transported across neuron and glial cells is also controversial, as the expression levels and functioning of the known protein capable to transport betaine expressed in the brain, betaine-GABA transporter 1 (BGT-1), is itself not well clarified. The reported actions of betaine beyond BGT-1 related to neuronal degeneration and memory impairment are the focus of this work. With this review, we underline the scarcity of detailed molecular and cellular information about betaine action. Consequently, the requirement of detailed focus on and study of the interaction of this molecule with CNS components to sustain the therapeutic use of betaine