Addressing performance degradations in end-to-end congestion control has been one of the most active research areas in the last decade. A huge number of techniques have been proposed in the past, but some of them miss the challenging target of both minimizing network delay and keeping goodput close to the network capacity (e.g., active queue management (AQM) techniques); others require changes in both network routers and hosts that make them difficult to deploy [e.g., eXplicit Control Protocol (XCP)]. In a previous paper, a novel mechanism, called Active Window Management (AWM), has been proposed by the same authors with the aim of controlling the queue length in network routers, maintaining it almost constant to achieve no loss, while maximizing network utilization. The target of this paper is twofold: 1) carrying out a deep analysis of the AWM algorithm stability to evaluate the impact of some system parameters on the performance of the whole system; 2) demonstrating that AWM can be gradually introduced, maintaining the compatibility with the current Internet. An extensive numerical analysis is proposed to demonstrate that AWM stabilizes the queue around a target value with small oscillations.

Peer-to-peer (P2P) networks are emerging as an interesting alternative to media streaming delivery with respect to content delivery networks (CDN). Although several P2P protocols have been proposed to support video streaming with an adequate degree of quality of service (QoS), a critical point today is how to evaluate them and optimize their parameters. The difficulty lies in the fact that the behavior of the P2P overlay network and the one of the underlying packet network are closely related and need to be analyzed simultaneously. Ad-hoc simulators for each P2P architecture have been proposed but they neglect the interactions between peers and the underlying network. This paper proposes a new approach to P2P video streaming performance analysis and system design which provides a very accurate cross-layer simulation of the real behavior of P2P clients over TCP/IP networks. A fluid-flow approach has been adopted to simulate the behavior of the network elements supporting an emulated overlay network consisting of real implementations of P2P clients. The P2P SplitStream video streaming protocol is considered as a case study to demonstrate that the tool is able to capture performance parameters at both the overlay (e.g. inter description synchronization) and packet network levels (e.g. traffic source round-trip time and router queue behavior).

Many techniques have been proposed in the last few years to address performance degradations in end-to-end congestion control. Although these techniques require parameter tuning to operate in different congestion scenarios, they miss the challenging target of both minimizing network delay and keeping goodput close to the network capacity. In this paper we propose a new mechanism, called Active Window Management (AWM), which addresses these targets by stabilizing the queue length in the network gateways. AWM acts on the Advertised Window parameter in the TCP segment carrying the acknowledge, but it does not affect the TCP protocol. The proposed technique is implemented in the network access gateways, that is, in the gateways through which both the incoming and outgoing packets related to a given TCP connection are forced to go, whatever the routing strategy used in the network. We show that when the access gateways implementing AWM are the bottleneck in the networks, TCP performance is very close to that of a pseudo constant bit rate protocol providing no loss, while network utilization is close to one.

UMTS is designed to offer high bandwidth radio access with QoS assurances for multimedia communications. In particular, real-time video communications services are expected to become a successful experience under UMTS networks. In this context, a video transmission service can be designed over the basis that UMTS can provide either a constant bit rate data channel or a dynamic variable bit rate data channel adapted to load conditions. In this latter approach, which is more efficient for both the user and the service provider, multimedia sources have to be timely designed in order to adapt their output rate to the instantaneous allowed channel rate. The target of this paper is to define an analytical model of adaptive real-time video sources in a UMTS network where system resources are dynamically shared among active users.

In this paper we propose a Markovian model of BitTorrent. Unlike already developed works which capture demographic dynamics, it focuses on the behavior of individual peers. To this end, we center our attention on a generic peer, called tagged peer (TP); for each possible logical state of a BT peer-to-peer connection maintained by the TP, we consider a stochastic process which counts the number of such links, and characterize them according to their state. Validation is carried out and steady-state analysis is performed in order to illustrate how performance evaluation can be extracted from our model

In recent years sensor networks have gained a lot of interest for industrial applications. The target of this paper is to define an analytical framework to evaluate the transient behavior of a sensor network in which sensors implement the energy-saving technique of idle/active states. The model captures the behavior of the battery lifetime of each sensor, and is able to evaluate the distribution of the lifetime of the whole network

In the current Internet scenario increasing interest is being shown in quality of service (QoS) issues, so simulation and parameter tuning are becoming very hot topics. In this paper we present a user-friendly, easily expandable and time-saving tool, which is able to perform network simulation through fluid-flow models and parameter tuning with parallel genetic algorithms. All the network elements involved (TCP sources, links, routers and so on) are modeled with the fluid-flow approach as independent systems: their outputs only depend on their inputs and internal state variables. Network elements can be connected to each other by a powerful graphical interface. Subsequently the user can select network parameters to be optimized in order to achieve prearranged QoS guarantees. During this phase the tool adopts a parallel implementation of a genetic algorithm (GA) which reduces the execution time required for optimization. A case study is also presented.

With the advent of multimedia traffic over the Internet several TCP-friendly protocols have been developed to improve UDP with congestion control mechanisms. The most promising TCP-friendly protocol is the TFRC. This paper addresses a novel analytical model for TFRC traffic sources. The model is able to capture TFRC behavior and its dependence on the network congestion state. Moreover, the model includes the TFRC loss probability estimation algorithm performed by the receiver. In order to keep the model manageable, whatever the number of sources and network routers, a fluid-flow approach is used.

BitTorrent is today one of the largest P2P systems which allows file sharing for Internet users. Very little effort has been dedicated to this target up to now. The goal of this paper is to develop an analytical model of a free-rider in a BitTorrent network. Unlike previous analytical models which capture the behavior of the network as a whole, the proposed model is able to analyze the performance from the user perspective. The model is applied to a case study to evaluate performance in a real case, and to obtain some insights into the influence of BitTorrent parameters on system performance.