Papers by Manos Varvarigos
Ad Hoc Networks, 2009
We propose and evaluate the performance of a new MAC-layer protocol for mobile ad hoc networks, c... more We propose and evaluate the performance of a new MAC-layer protocol for mobile ad hoc networks, called the Slow Start Power Controlled (abbreviated SSPC) protocol. SSPC improves on IEEE 802.11 by using power control for the RTS/CTS and DATA frame transmissions, so as to reduce energy consumption and increase network throughput and lifetime. In our scheme the transmission power used for the RTS frames is not constant, but follows a slow start principle. The CTS frames, which are sent at maximum transmission power, prevent the neighbouring nodes from transmitting their DATA frames at power levels higher than a computed threshold, while allowing them to transmit at power levels less than that threshold. Reduced energy consumption is achieved by adjusting the node transmission power to the minimum required value for reliable reception at the receiving node, while increase in network throughput is achieved by allowing more transmissions to take place simultaneously. The slow start principle used for calculating the appropriate DATA frames transmission power and the possibility of more simultaneous collision-free transmissions differentiate the SSPC protocol from the other MAC solutions proposed for IEEE 802.11. Simulation results indicate that the SSPC protocol achieves a significant reduction in power consumption, average packet delay and frequency of RTS frame collisions, and a significant increase in network throughput and received-to-sent packets ratio compared to IEEE 802.11 protocol.
Education, IEEE …, Jan 1, 2007
The Greek School Network (GSN) is a closed nationwide educational network that offers advanced te... more The Greek School Network (GSN) is a closed nationwide educational network that offers advanced telematic and networking services to all primary/secondary education schools and administration offices in Greece. The primary objective of GSN is the provisioning of a network infrastructure for the interconnection of school PC laboratories so that modern educational methods and pedagogical models can be applied to the school community. GSN has scaled in size, has reached maturity, and is currently delivering a wide range of network and telematic services to its users. The emerging power of open-source software provides a sound technological basis for building cutting-edge services, capable of meeting internal administrative and monitoring needs, and modern pedagogical requirements for tools and services. The current paper presents an overview of GSN and an evaluation of its services based on the opinions of its users, and on service utilization and traffic measurement statistics. The paper reaches the conclusion that open-source solutions provide a sound technological platform that can cover, to a great extent, the needs for advanced educational services of the school community.
Proc. Int. Joint Conf. E- …, Jan 1, 2006
The Greek School Network (GSN) is a closed educational network that offers advanced telematic and... more The Greek School Network (GSN) is a closed educational network that offers advanced telematic and networking services to all units of primary and secondary education schools and administration offices in Greece. The main objective of GSN is the implementation of a network infrastructure for the interconnection of the school laboratories and the provision of a wide range of network and telematic services to students and teachers. The GSN separates its telematic services to two major groups: the centralized services and the end-user services. The purpose of this paper is to describe the GSN structure, the services it provides, and its design and operational principles.
ICSSSM12, 2012
Managing the IT environment of large organizations such as the Greek School Network is challengin... more Managing the IT environment of large organizations such as the Greek School Network is challenging not only due to the complexity, diversity and age of the information processing infrastructure but also due to geographic dispersion and the IT support model. Recently, the Network attempted to follow known practices for IT enterprise management; in order to organize and automate both supervision and intervention it employed centralized system management architectures. This paper records the challenges encountered in order to configure a deployable, high-end enterprise platform for the management of school labs across the Greek School Network. The paper reaches the conclusion that such systems or services are not always straightforward to deploy or scale and discusses alternative directions that can bring general purpose infrastructure management for organisations that cannot benefit from enterprise systems yet are still in need of analogous functionality.
The Greek School Network (GSN) is a closed educational network that offers advanced telematic and... more The Greek School Network (GSN) is a closed educational network that offers advanced telematic and networking services to all primary/secondary education schools and educational administration offices in Greece. The primary objective of GSN is to provide a network infrastructure for the interconnection of school PC laboratories so that modern educational methods and pedagogical models can be used in the school community securely and effectively. GSN has scaled in size, reached maturity, and is currently delivering a wide range of network and telematic services to students and educators. Being the second largest communications network nationwide, GSN is exposed to all kinds of security threats and, due to its educational hypostasis, naive user behaviour. The current paper presents an evaluation of security management solutions for the enforcement of policies, practices, and user protection methodologies proven viable within the GSN environment, as indicated by statistics and metrics on the use of the related services. The paper reaches the conclusion that GSN security services constitute a sound framework that can successfully cover the needs of the school community.
—The Greek School Network (GSN) is a closed nationwide educational network that offers advanced t... more —The Greek School Network (GSN) is a closed nationwide educational network that offers advanced telematic and networking services to all primary/secondary education schools and administration offices in Greece. The primary objective of GSN is the provisioning of a network infrastructure for the inter-connection of school PC laboratories so that modern educational methods and pedagogical models can be applied to the school community. GSN has scaled in size, has reached maturity, and is currently delivering a wide range of network and telematic services to its users. The emerging power of open-source software provides a sound technological basis for building cutting-edge services, capable of meeting internal administrative and monitoring needs, and modern pedagogical requirements for tools and services. The current paper presents an overview of GSN and an evaluation of its services based on the opinions of its users, and on service utilization and traffic measurement statistics. The paper reaches the conclusion that open-source solutions provide a sound technological platform that can cover, to a great extent, the needs for advanced educational services of the school community.
2013 IEEE 20th Symposium on Communications and Vehicular Technology in the Benelux (SCVT), 2013
ABSTRACT The fairness aspect on handling user data flows in modern broadband telecommunication ne... more ABSTRACT The fairness aspect on handling user data flows in modern broadband telecommunication networks is of paramount importance since it strongly affects the quality of the provided services. In this work, the fairness provisioning is investigated in a competitive telecommunication field such as the passive optical networks (PONs). Intending to resolve unequal resource allocation in the downstream data delivery, a fair bandwidth assignment scheme is devised and evaluated. The Max-Min fairness concept is applied in order to determine the best effort (BE) bandwidth allocation of each optical network unit (ONU) in the optical line terminal (OLT) side. Simulation results indicate the benefits of utilizing the proposed resource allocation technique in terms of fair bandwidth distribution.
2014 6th International Congress on Ultra Modern Telecommunications and Control Systems and Workshops (ICUMT), 2014
ABSTRACT
Current VLSI technology allows more than two wiring layers and the number is expected to rise in ... more Current VLSI technology allows more than two wiring layers and the number is expected to rise in future. In this paper, we show that, by designing VLSI layouts directly for an L-layer model, the layout area for a variety of networks can be reduced by a factor of about (L=2) 2 compared to the layout area required under a 2-layer model, and the volume and maximum wire length can be reduced by a factor of about L=2, leading to considerably lower cost and/or higher performance. The proposed layouts for k-ary n-cubes, hypercubes, butterfly networks, cube-connected cycles (CCC), folded hypercubes, generalized hypercubes, k-ary n-cube cluster-c, hierarchical hypercube networks, reduced hypercubes, hierarchical swap networks, and indirect swap networks, are the best layouts reported for these networks thus far and are optimal within a small constant factor under both the Thompson model and the multilayer grid model. All of our layouts are optimally scalable in that we can allow each network node to occupy the largest possible area (e.g., o(N=L 2 ) for hypercubes) without increasing the leading constant of the layout area, volume, or maximum wire length.
Proceedings of the twelfth annual ACM symposium on Parallel algorithms and architectures - SPAA '00, 2000
Lecture Notes in Computer Science, 2007
We propose new burst assembly techniques that aim at reducing the average delay experienced by th... more We propose new burst assembly techniques that aim at reducing the average delay experienced by the packets during the burstification process in optical burst switched (OBS) networks, for a given average size of the bursts produced. These techniques use a linear prediction filter to estimate the number of packet arrivals at the ingress node in the following interval, and launch a new burst into the network when a certain criterion, which is different for each proposed scheme, is met. Reducing the packet burstification delay, for a given average burst size, is essential for real-time applications; correspondingly, increasing the average burst size for a given packet burstification delay is important for reducing the number of bursts injected into the network and the associated overhead imposed on the core nodes. We evaluate the performance of the proposed schemes and show that two of them outperform the previously proposed timer based, length based and average delay-based burst aggregation schemes in terms of the average packet burstification delay for a given average burst size.
2006 IEEE 17th International Symposium on Personal, Indoor and Mobile Radio Communications, 2006
ABSTRACT We propose a MAC protocol for mobile ad hoc networks that uses power control for the RTS... more ABSTRACT We propose a MAC protocol for mobile ad hoc networks that uses power control for the RTS/CTS and DATA frame transmissions in order to improve energy and capacity utilization efficiency. Unlike IEEE 802.11, in our scheme the RTS frames are not sent using the maximum transmission power to silence neighbouring nodes, and the CTS frames do not silence all receiving nodes to the same degree. In contrast, the transmission power of the RTS frames follows a slow start principle, while the CTS frames, which are sent at maximum transmission power, prevent the neighbouring nodes from transmitting their DATA frames with power more than a computed threshold, while allowing them to transmit at power levels less than that threshold. This is done by including in the RTS and the CTS frames additional information, such as the power of the transmissions, and the interference tolerance of the nodes. Moreover the DATA frames are sent at the minimum required transmission power increased by a small margin to ensure connectivity with the intended receiver, so as to cause minimal interference to neighbouring nodes and allow for future interference to be added to the receiver of the DATA frames. The power to be used by the transmitter is computed by the recipient of the RTS frame and is included in the CTS frame. It is expected that a network with such a power management scheme would achieve a better throughput performance and more power savings than a network without such a scheme
We present a new architecture for bufferless, asynchronous all-optical self-routing network combi... more We present a new architecture for bufferless, asynchronous all-optical self-routing network combining an efficient physical layer structure and conflict-preventing signaling protocol for providing lossless communication with optimum resource utilization and QoS differentiation.
Grids offer a transparent interface to geographically scattered computation, communication, stora... more Grids offer a transparent interface to geographically scattered computation, communication, storage and other resources. In this chapter we propose and evaluate QoS-aware and fair scheduling algorithms for Grid Networks, which are capable of optimally or near-optimally assigning tasks to resources, while taking into consideration the task characteristics and QoS requirements. We categorize Grid tasks according to whether or not they demand hard performance guarantees. Tasks with one or more hard requirements are referred to as Guaranteed Service (GS) tasks, while tasks with no hard requirements are referred to as Best Effort (BE) tasks. For GS tasks, we propose scheduling algorithms that provide deadline or computational power guarantees, or offer fair degradation in the QoS such tasks receive in case of congestion. Regarding BE tasks our objective is to allocate resources in a fair way, where fairness is interpreted in the max-min fair share sense. Though, we mainly address scheduling problems on computation resources, we also look at the joint scheduling of communication and computation resources and propose routing and scheduling algorithms aiming at co-allocating both resource type so as to satisfy their respective QoS requirements.
Future Grid Networks should be able to provide Quality of Service (QoS) guarantees to their users... more Future Grid Networks should be able to provide Quality of Service (QoS) guarantees to their users. In this work we examine the way Grid resources should be configured so as to provide deterministic delay guarantees to Guaranteed Service (GS) users and fairness to Best Effort (BE) users. The resources are partitioned in groups that serve GS users only, or BE users only, or both types of users with different priorities. Furthermore, the GS users are registered to the resources either statically or dynamically, while both single and multi-Cpu resources are examined. Finally the proposed resource configurations for providing QoS are implemented in the GridSim environment and a number simulations are executed.
In this paper we present the Efficient Burst Reservation Protocol (EBRP) suitable for bufferless ... more In this paper we present the Efficient Burst Reservation Protocol (EBRP) suitable for bufferless Optical Burst Switching networks. The EBRP protocol is a two-way reservation scheme that employs timed and in-advance reservation of resources. In the EBRP protocol timed reservations are relaxed, introducing a reservation time duration parameter that is negotiated during call setup phase. This feature allows bursts to reserve resources beyond their actual size to increase their successful forwarding probability and can be used to provide QoS differentiation. The EBRP protocol is suitable for OBS networks and can guarantee a low blocking probability for bursts that can tolerate the round-trip delay associated with the two-way reservation. In this paper, we present the main features of the proposed protocol and describe in detail, timing considerations regarding the call setup phase and the actual reservation process. Furthermore, we show evaluation results and compare the EBRP performance against two other typical reservation schemes, a TAW and a TAG (JET) like protocol. EBRP has been developed for the control plane of the IST-LASAGNE project.
Journal of Optical Networking, 2006
In this paper we present the efficient burst reservation protocol (EBRP) suitable for bufferless ... more In this paper we present the efficient burst reservation protocol (EBRP) suitable for bufferless optical burst switching (OBS) networks. The EBRP protocol is a two-way reservation scheme that employs timed and in-advance reservation of resources. In the EBRP protocol timed reservations are relaxed, introducing a reservation time duration parameter that is negotiated during call setup phase. This feature allows bursts to reserve resources beyond their actual size to increase their successful forwarding probability and can be used to provide quality-of-service (QoS) differentiation. The EBRP protocol is suitable for OBS networks and can guarantee a low blocking probability for bursts that can tolerate the round-trip delay associated with the two-way reservation. We present the main features of the proposed protocol and describe in detail the timing considerations regarding the call setup phase and the actual reservation process. Furthermore, we show evaluation results and compare the EBRP performance against two other typical reservation schemes, a tell-and-wait and a tell-and-go (just-enough-time) like protocol. EBRP has been developed for the control plane of the IST-LASAGNE project.
We propose a general policy to allocate subcarriers to time-varying traffic in a flexible OFDM op... more We propose a general policy to allocate subcarriers to time-varying traffic in a flexible OFDM optical network. We compare the OFDM network performance to that of a fixed-grid WDM network using simulations.
2006 3rd International Conference on Broadband Communications, Networks and Systems, 2006
In this paper we present a signaling protocol for QoS differentiation suitable for optical burst ... more In this paper we present a signaling protocol for QoS differentiation suitable for optical burst switching networks. The proposed protocol is a two-way reservation scheme that employs delayed and in-advance reservation of resources. In this scheme delayed reservations may be relaxed, introducing a reservation duration parameter that is negotiated during call setup phase. This feature allows bursts to reserve resources beyond their actual size to increase their successful forwarding probability and is used to provide QoS differentiation. The proposed signaling protocol offers a low blocking probability for bursts that can tolerate the round-trip delay required for the reservations. We present the main features of the protocol and describe in detail timing considerations regarding the call setup and the reservation process. We also describe several methods for choosing the protocol parameters so as to optimize performance and present corresponding evaluation results. Furthermore, we compare the performance of the proposed protocol against that of two other typical reservation protocols, a Tell-and-Wait and a Tell-and-Go protocol.
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Papers by Manos Varvarigos