Papers by Edmundo Monteiro
Abstract Wireless Sensor Networks (WSNs) are no longer limited to scenarios of uncontrolled perfo... more Abstract Wireless Sensor Networks (WSNs) are no longer limited to scenarios of uncontrolled performance. A new emerging range of applications demand specific Quality of Service (QoS) assurance and the support of critical scenarios. However, QoS in WSNs, and a reference model to characterize and measure it, are yet challenges to be met. In this paper, a new taxonomy of WSNs with QoS is proposed, including information and communication perspectives. The goal is to contribute to the establishment of a reference ...
Resumo No Laboratório de Comunicações e Telemática (LCT) da Universidade de Coimbra foi desenvolv... more Resumo No Laboratório de Comunicações e Telemática (LCT) da Universidade de Coimbra foi desenvolvido um modelo de qualidade de serviço (QoS), designado por modelo LCT−QoS, baseado no paradigma Differentiated Services (DiffServ) da Internet Engineering Task Force (IETF). O modelo desenvolvido inclui funcionalidades para diferenciar tráfego e capacidades para fornecer qualidade de serviço às aplicações que o necessitem. Integrando o modelo LCT−QoS foi desenvolvido um novo Per Hop Behavior (PHB), designado por Distribuição Dinâmica da Degradação (PHB-D3). O funcionamento do PHB−D3 baseia-se na distribuição dos recursos da rede de forma dinâmica pelas diferentes classes de tráfego, em função dos requisitos de qualidade de serviço e da sensibilidade à degradação associados a cada classe, sem que, para isso, seja necessário efectuar grandes alterações na tecnologia IP. Com este artigo pretende-se dar continuidade à avaliação em curso do PHB−D3. Para isso, o PHB−D3 foi sujeito a testes int...
GLOBECOM - IEEE Global Telecommunications Conference, 2008
In this paper we propose Open Box Transport Protocol (OBP), a mechanism that provides information... more In this paper we propose Open Box Transport Protocol (OBP), a mechanism that provides information to the end systems about the current state of the network path. With this information (essentially the available bandwidth and the most restricted link capacity) the end systems can efficiently use the network resources. OBP is easy to implement because the intermediate nodes only have to p rovide information about the current network state to the end systems, and don't have to estimate the transmission rate of the flows. The coexistence of flows from OBP and other transport protocols in the same link does not introduce additional problems because t he transmission rate of OBP flows is estimated at the sender end system.
In this paper we study the stability of Open Box Transport Protocol (OBP), an explicit congestion... more In this paper we study the stability of Open Box Transport Protocol (OBP), an explicit congestion control protocol that provides information to the end systems about the current state of the network path. To support the study we deduced the OBP transfer function to study the protocol stability, which modulates the OBP behavior at equilibrium. In the stability evaluation we use Bode and Nyquist diagrams. The OBP stability characteristics, discussed in this work, are only related with the equilibrium phase, which means when all the ...
Proceedings - IEEE Symposium on Computers and Communications, 2009
Abstract In this paper we study the stability of the Open Box Transport Protocol (OBP), an explic... more Abstract In this paper we study the stability of the Open Box Transport Protocol (OBP), an explicit congestion control protocol that provides information to the end systems about the current state of the network path. To support the study we deduced the OBP transfer function, which modulates the OBP behavior at equilibrium. In the stability evaluation we use Bode and Nyquist diagrams. The OBP stability characteristics, discussed in this work, are only related with the equilibrium phase, in other words when all the network capacity is in use. ...
… , 1999. IEEE Workshop …, Jan 1, 1999
Lecture Notes in Computer Science, 2007
In this paper we propose a new explicit congestion control approach, Open Box Protocol (OBP). Thi... more In this paper we propose a new explicit congestion control approach, Open Box Protocol (OBP). This is an approach which provides important information to traffic sources, about the network path state. This solution enables an efficient use of the network capacity, since the sources make congestion control decisions based on information about the network path state, which carries traffic from the sources to the destinations end systems. The OBP gives sources the capacity to look inside the network and to make their congestion control decisions, based, not only on packets loss or packets delay, but also based on another kind of information. For example, the most restricted interface capacity, the available bandwidth, the RTT variations or the presence of heterogeneous transmission means. In the paper we describe the OBP and discuss its evaluation results based on ns-2 simulations. The results show the OBP´s capacity to provide traffic sources with the required information, in static or dynamic network scenarios, and to make correct and quick congestion control decisions. Also, it is visible that the OBP avoids the full queue problem and tries to keep the queues near zero occupation. Moreover the results show that with the OBP it is possible to obtain better throughput than other explicit congestion control protocols, avoid congestion and simultaneously keep the queues near zero occupation.
Idms, 2002
We present a hierarchical multimedia archive that can serve complex multimedia requests from tert... more We present a hierarchical multimedia archive that can serve complex multimedia requests from tertiary storage. Requests can consist of multiple request units of streamed and non-streamed data. The request units can have arbitrary synchronization patterns. Our scheduler Promote-IT promotes data from tertiary to secondary storage with real-time guarantees. Promote-IT uses an on-line heuristic algorithm to compute feasible schedules and a separate ASAP dispatcher to increase the efficiency of the resource usage. The heuristic algorithm runs in polynomial time. Schedules are optimized to give short response times to incoming requests. Three major problems complicate this scheduling problem. First, the fragments of requested real-time data and their synchronization are unpredictable. Second, the medium switching times in tertiary storage are high, and the number of drives and robots is low compared to the number of removable media. Third, the shared resources in the tertiary storage system create resource contention problems.
Palavras chave: Políticas de Segurança, Firewalls, SPSL. Resumo Neste artigo é apresentada uma fe... more Palavras chave: Políticas de Segurança, Firewalls, SPSL. Resumo Neste artigo é apresentada uma ferramenta de descrição de Políticas de Segurança, baseada na linguagem SPSL (Security Policy Specification Language). A ferramenta permite efectuar a descrição de políticas de segurança posteriormente utilizadas na criação e difusão de regras reconhecidas por vários equipamentos na implementação das políticas de segurança das organizações.
10th IEEE International Conference on Electronics, Circuits and Systems, 2003. ICECS 2003. Proceedings of the 2003, 2003
Modems and other network interfaces are critical devices in a network infrastructure. While softw... more Modems and other network interfaces are critical devices in a network infrastructure. While software modems would be the ideal solution for flexibility and low cost, they miss the speed performance requirement. On the other hand, the usual hardware specific approach is not adapted to the fast evolution of protocols in modern multimedia network applications, in which very high data rates,
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Papers by Edmundo Monteiro