Enrico Gregori

Smartphone-based crowdsourcing for network monitoring: Opportunities, challenges, and a case study

Smartphone-based crowdsourcing fosters the rise of radically novel systems and applications in the context of network monitoring. This article discusses the most significant opportunities offered by this approach, and the major challenges that have to be faced. Our experience in building a smartphone-based crowdsourcing system, Portolan, is also included to provide a practical background to the discussion and to demonstrate the possible benefits.

Wireless access to internet via Bluetooth: performance evaluation of the EDC scheduling algorithm

Bluetooth is an emerging technology for constructing adhoc wirelessPersonal Area Networks (WPANs). In this paper we analyze aninnovative scheduling algorithm for asynchronous data trafficspecifically tailored to the Bluetooth characteristic. Thisalgorithm, named Efficient Double-Cycle (EDC), dynamically adaptsthe polling frequency to the traffic conditions. By considering ascenario where a Bluetooth master is used as wireless access pointto the Internet, we show that our EDC scheduler significantlyenhances the system performance with regard to a Round Robin (RR)scheduler.

A power-aware multimedia streaming protocol for mobile users

Smart environments are becoming popular and even more users are approaching their services through portable devices like PDAs, laptops, and mobile phones. These devices are generally battery-fed, thus, energy efficiency is surely a critical factor for the deployment of pervasive services. In this paper we focus on the diffusion of multimedia streaming services in smart environments. Specifically, we investigate scenarios where mobile users who have a Wi-Fi access to the Internet receive audio files from remote streaming servers. We address energy saving by including periodic transmission interruptions in the schedule of audio frames at the server, so that the network interface card at the receiver can be set to a low-power consuming state. Experimentation on a software prototype shows that our solution makes possible an energy saving ranging from 76% to 91% (depending on the data rate and the background traffic) of the total consumption due to the network interface. It also preserves a good user level QoS.

Balancing energy saving and QoS in the mobile Internet: an application-independent approach

The scarcity of energetic resources in mobile computers is a very limiting factor. In this paper we propose a solution that tries to balance energy consumption and QoS requirements. Our solution follows an application-independent approach and, therefore, it can be used concurrently, and without modifications, by any network application. Furthermore, our solution is independent from the sub-network technology. We implemented this solution and we extensively tested it. Experimental results have shown that a relevant energy saving (about 70% on average) can be achieved with respect to the legacy approach based on the TCP/IP protocol stack. Furthermore, these savings are obtained without a significant degradation in the QoS perceived by the user. We also compared our application-independent approach with an application-dependent one (i.e., a solution tailored to Web browsing) which performs (slightly) better. However, the application-independent solution still guarantees significant savings, and fits better a general-purpose mobile environment.

Fiber-Distributed Data Interface (FDDI)

The standard FDDI [4] describes a high-speed MAC protocol for LANs/MANs which employs a timer-controlled, token-passing mechanism, called a timed token protocol, to control each station’ s access to the shared medium.

Validation and tuning of an MPEG-1 video model

Variable Bit Rate (VBR) video traffic is expected to become one of the major traffic sources for high-speed networks. Although the modeling of VBR video sources has recently received significant attention, there is currently no widely accepted model which lends itself to mathematical analysis. This paper addresses the problem of characterizing the traffic generated by VBR video applications. Specifically, we define an analytically tractable model for the traffic generated by an MPEG-1 encoder. An extensive validation of this model is carried out by analyzing its suitability to capture the statistical behavior of a wide variety of MPEG-1 sources ranging from movies, sports events, talk shows, etc. We show that our model, with an adequate tuning of its parameters, is able to provide an accurate representation of these different kinds of MPEG-1 sources.

DQDB/FBS: A fair MAC protocol stemming from DQDB fairness analysis

DQDB (distributed queue dual bus) is a media access control (MAC) protocol which is being standardized in IEEE 802 as an 802.6 metropolitan area network (MAN) standard proposal. The authors analyze the major features responsible for unfairness in the DQDB MAC protocol with the bandwidth balancing mechanism disabled. For each of these factors mechanisms to reduce the unfairness are identified and analyzed. These new mechanisms are brought together in a unique MAC protocol named DQDB/FBS (fair bandwidth sharing) which, while preserving the DQDB distributed queue concept, implements a new reservation mechanism. The performance analysis of DQDB/FBS shows a remarkable improvement in fairness. In particular, ideal fair behavior is obtained under heavy loads. A comparison between DQDB (BWBMOD=8) and DQDB/FBS is provided, and the pros and cons of both MAC protocols are highlighted.<<ETX>>

MPEG-2 variable bit rate coding algorithm: analysis and modeling

Variable bit rate (VBR) video is currently by far the most interesting and challenging real-time application for B- ISDN/ATM environments. To define bandwidth allocation schemes which provide an adequate quality of service (QoS) for VBR applications and minimize the waste of bandwidth, the effects of the video applications on the network must be investigated. While the modeling of VBR video sources has recently received significant attention, there presently exists no widely accepted model which lends itself to mathematical analysis. Currently MPEG is the reference standard for moving video compression. In the first part of the paper a VBR implementation of MPEG-2 coding algorithm is described and a comparison with the constant bit rate (CBR) algorithm is performed. To investigate the impact that the coding parameters have on the characteristics of the traffic delivered to the network a long sample of the movie The Sheltering Sky has been coded with two different quantizer steps. The generated trace was used to obtain a detailed statistical analysis of the traffic generated by an MPEG-2 encoder. Starting from this statistical analysis an analytically tractable model is developed, analyzed and used to study bandwidth allocation problems.

An M/G/1 type approach to the approximation of the slot-occupancy pattern in a DQDB network

Abstract In a previous paper, we presented a method for approximating the process that models the status of consecutive slots traveling on the forward bus in a DQDB network (slot-occupancy-pattern process) in underload conditions. That method models the slot-occupancy-pattern process of a simplified DQDB network, which behaves similarly to DQDB, by using an nth-order discrete-time Markov process. Because of its computational complexity, the method was applied only to evaluate the 1st and 2nd-order approximations. By noting that the nth-order discrete-time Markov process is a Markov chain of M/G/1 type, here we exploit the basic methodology developed for such chains by Neuts and the recursion algorithm of Ramaswami to derive the steady-state probabilities. We investigate special features of the Markov chain that induce a significant complexity reduction of the algorithm for its solution. From the steady-state probabilities, we obtain the network configurations and the workload conditions for which the simplified DQDB is close to real DQDB. The accuracy of our results was tested by simulation. Finally, through a hybrid analytic/simulation approach we study the influence of the slot-occupancy-pattern model on the access delay experienced by users in a DQDB network.

Stochastic Processes For Modeling Metropolitan Area Networks: Basic Results

Two classes of queueing models are generally used to model MAC protocols for MANs: single server queueing system and polling systems. This chapter introduces these models and reviews their basic properties.