Kostas Stamos

An adaptive admission control algorithm for bandwidth brokers

This work focuses on the operation of the bandwidth broker, an entity that is responsible for managing the bandwidth within a network domain and for the communication with bandwidth brokers of neighboring domains. A very important aspect of the bandwidth broker is its admission control module that determines whether the bandwidth reservation requests are going to be accepted or not. We summarize the status of the current research in this field and propose architecture for the admission control module that aims at achieving a satisfactory balance between maximizing the resource utilization for the network provider and minimizing the overhead of the module. This is achieved by gathering and examining sets of book-ahead requests and by adapting the size of the set to be examined so that the network utilization and the computation overhead are appropriately balanced.

Application on demand system over the Internet

This paper describes the design and implementation of the ASP-NG system. The main modules of the ASP-NG system are the AoD service and the Web Portal. The ASP-NG Portal is a portal for providing the user with the necessary interface in order to access an Application on Demand (AoD) service. The ASP-NG portal is responsible for the interaction with the user of the AoD service. Using the AoD service the user rents an application for a limited time period at a fraction of the actual cost of the application. The AoD service is responsible for downloading the appropriate parts of the application according to the users actions, while enforcing the mutually agreed frame between the user and the Application Service Provider (ASP). The implementation of the ASP-NG portal is based on the Web Services of the Java 2, Enterprise Edition platform and the implementation of the AoD module is based on C + + programming language. The ASP-NG portal offers to its users the capability to select and customize the language of the user interface in order to present information in their preferred language. Moreover the ASP-NG portal offers to the portal administrator the capability to customise the look and feel of the ASP-NG portal.

An efficient architecture for bandwidth Brokers in DiffServ networks

In this article we examine the architecture of an entity used for automatic management and provisioning of resources for DiffServ networks. We examine the existing literature and implementations in this area, focusing on the design choices made, and we propose an architecture for the design of Bandwidth Brokers that combines an adaptive admission control algorithm for increased utilization of network resources and a mechanism for reducing the complexity overhead that intends to be both simple and effective. Specifically, we present a novel architecture for the admission control module that aims at achieving a satisfactory balance between maximizing the resource utilization for the network provider and minimizing the overhead of the module. We complement our theoretical discussion with extensive experimental simulations for the proposed Bandwidth Broker components and analysis of the results. The simulations study the possible configurations of the proposed algorithm and also compare it with alternative admission control policies.

A tool for automating network simulation and processing tracing data files

Abstract One of the most highly regarded discrete event simulators used for network simulation is NS-2 (Network Simulator). NS-2 executes simulation scenarios producing various data of which trace files are considered the most beneficial for evaluating a simulation. In this paper we present the design considerations and implementation of a new tool that can be used both in TRAce FILe analysis and execution of simulations using NS-2. Although TRAFIL is primarily based on NS-2 trace files it can be extended to support a number of different other simulation trace file formats. It aims to make the execution of a great number of network simulations quicker, and the extraction of results from a large amount of data more flexible and productive. In order to accomplish the above tasks TRAFIL presents a novel way of interpreting, parsing, reading and eventually using NS-2 trace files. It introduces the notion of “metafiles” and “sub metafiles” throughout the procedures of trace file recognition and parsing, making the overall analysis operation substantially efficient and faster than alternative approaches. Metafiles and sub metafiles are used to encode NS-2 trace file structures enabling a more abstract approach to the trace file processing operation. Furthermore, TRAFIL facilitates the overall trace file analysis task by offering the opportunity to store each trace file as well as every Quality of Service (QoS) measurement produced for each trace file. Following the trace file recognition and processing operations, the information contained in a trace file is presented through a Graphical User Interface (GUI) offered by TRAFIL along with a variety of data, metrics and statistics related to simulation results. Finally, the tool offers the opportunity to execute custom Structured Query Language (SQL) queries to the local database and to completely automate the simulation procedure by enabling the user to execute NS-2 scripts as well as perform a simulation of a video transmission using the Evalvid-RA framework.

Performance Evaluation of the Impact of QoS Mechanisms in an IPv6 Network for IPv6-Capable Real-Time Applications

This paper describes a Quality of Service (QoS) service on an IPv6 domain that aims to service aggregates of real-time traffic with minimum delay, jitter, and packet loss. It contains results from the tests that were performed in order to configure and evaluate the QoS mechanisms. As an actual example of real-time traffic, we have used the OpenH323 project, an open source H.323 implementation that has been ported to IPv6. The QoS mechanisms in IPv6 networks is still a field that has not been researched adequately, and we therefore present the results from the experiments in our IPv6 network that took advantage of the QoS mechanisms. This QoS service uses the Modular QoS CLI (MQC) mechanism and especially the Low Latency Queue feature (LLQ) in order to treat packets from real-time applications.

Examining the benefits of a hybrid distributed architecture for bandwidth brokers

In this paper the issue of the architectural organization of a bandwidth broker with respect to the distribution of functionalities among separate entities is examined. We discuss the benefits of a distributed versus a centralized architecture and study some of the most important implementations. We also present a novel design proposal that builds on our earlier work on the admission control module of a bandwidth broker and introduces it in the framework of a distributed bandwidth broker architecture. Our conclusions are supported by a series of simulated experiments that we analyze.

Extending QoS support from Layer 3 to Layer 2

This paper presents some of the results obtained by the application of Ethernet layer 2 quality of service in IP networks. IP networks traditionally provide quality of service in Layer 3. However, since there is an enormous existing Layer 2 infrastructure, todaypsilas networks could benefit from the deployment of Layer 2 quality of service and the cooperation between layer 2 quality of service and layer 3 quality of service. In this paper, experiments are suggested and conducted and a scheme is suggested for efficient cooperation between Layer 2 and Layer 3 QoS provisioning.

Architecture and Performance Evaluation for Redundant Multicast Transmission Supporting Adaptive QoS

In this paper we describe the architecture of an application that was developed for the transmission of multimedia data, using the multicast mechanism, over the Internet. There are two major issues that have to be considered when designing and implementing such a service, the fairness and the adaptation schemes. The fairness problem results from the fact that Clients with different capabilities have to be served. In our application we use a mechanism that categorizes the Clients into a number of groups according to each Clients capabilities and (the mechanism) serves each group of Clients with a different multicast stream. With the term “capabilities” we do not only mean the processing power of the Client, but also the capacity and the condition of the network path towards that Client. Because of todays Internet heterogeneity and the lack of Quality of Service (QoS) support, the Server cannot assume that the Clients will permanently be able to handle a specific bit rate. We have therefore implemented an additional mechanism for the intra-stream bit rate adaptation. The proposed mechanism uses a “friendly” to the network users congestion control policy to control the transmission of the data. We evaluate the adaptive multicast transmission mechanism through a number of experiments and a number of simulations in order to examine its behaviour to a heterogeneous group of Clients and its behaviour against TCP and UDP data streams.

Efficient Power Management Adaptation for Video Transmission over TFRC

In this paper, we describe a power management mechanism for wireless video transmission using the TFRC protocol that takes into account feedback about the received video quality and tries to intelligently adapt transmitting power accordingly. The purpose of the mechanism is to utilize TFRC feedback and thus achieve a beneficial balance between the power consumption and the received video quality. We use simulation in order to compare and evaluate our approach.

Performance evaluation of an IPv6-capable H323 application

OpenH323 is an open source H.323 implementation that has been ported to IPv6. In this paper we briefly introduce the library architecture and the performance criteria with which the ported version should be evaluated. We then present a variety of experiments that we conducted in order to comparatively evaluate the IPv4 and IPv6 protocol stacks. We also present the results of some initial experiments comparing IPv4 and IPv6 performance under congested network links and the conclusions that they lead us to.