Marco Conti

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.

TPA: a transport protocol for ad hoc networks

Several previous works have shown that TCP exhibits poor performance in mobile ad hoc networks (MANETs). The ultimate reason for this is that MANETs behave in a significantly different way from traditional wired networks, like the Internet, for which TCP was originally designed. In this paper we propose a novel transport protocol - named TPA - specifically tailored to the characteristics of the MANET environment. It is based on a completely new congestion control mechanism, and designed in such a way to minimize the number of useless transmissions and, hence, power consumption. Furthermore, it is able to manage efficiently route changes and route failures. We evaluated the TPA protocol in a static scenario where TCP exhibits good performance. Simulation results show that, even in such a scenario, TPA significantly outperforms TCP.

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.

Routing, Interface Assignment and Related Cross-layer Issues in Multiradio Wireless Mesh Networks

Many technological standards for Wireless Mesh Networks include the possibility to use several nonoverlapping channels for data transmission. This represents an opportunity that can be exploited by equipping the terminals with multiple network interfaces. This opens up an interesting challenge, namely, how to simultaneously use different frequencies, so as to limit collisions and therefore activate multiple simultaneous transmissions in the same geographic area. At the same time, this poses new issues; for example, network connectivity is reduced, because nodes that do not interfere are also unable to communicate with each other. Thus, more complex interface management techniques are required. Moreover, a paradigm shift from the classic routing schemes is needed. Usual approaches are not always satisfactory because they often use shortest-path heuristic and tend to concentrate transmissions to certain nodes. To efficiently exploit the presence of multiple channels instead, a proper routing algorithm should avoid congested links and possibly make use of an estimation of the actual network traffic. Therefore, cross-layer information exchange can be useful for an efficient functioning of the routing protocols. In this chapter, we will analyze all these issues and propose and identify possible solutions.

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.

DQDB modeling: problem complexity reduction and solution via Markov chains

Abstract This paper presents a novel approach to DQDB modeling; the innovative aspect lies in the attempt to provide an accurate representation of the process of the busy slots travelling on the forward bus. We show in the paper that for aggregate loads exceeding 80% of the medium capacity, the Bernoulli hypothesis generally used for modeling the length of busy trains diverges greatly from the actual behavior. In this paper, by assuming that consecutive busy trains form a sequence of i.i.d. random variables, we compute the busy train statistics via a Markov chain approach. The results obtained show a marked improvement, compared to the Bernoulli hypothesis. Using our busy train statistics we have obtained an approximation of the bus access delay for each node of a DQDB network 1 .

Reliable data delivery in sparse WSNs with multiple Mobile Sinks: An experimental analysis

Urban sensing is emerging as a significant Wireless Sensor Networks (WSNs) application. In such a scenario, static sensors are sparsely deployed in an urban area to collect environmental information. Sensed data are opportunistically collected by Mobile Sinks (MSs), which can be other sensor nodes attached to cars or buses, or carried by people while they move around the city. Since the contacts between the MSs and the static sensors are infrequent and short, reliable and energy efficient data collection is a primary concern of such applications. To this end, we exploit a hybrid data delivery scheme based on both Erasure Coding (EC) and feedback by the MSs. We provide an optimized implementation, and show by extensive experiments in a real testbed that the proposed approach is feasible, despite the very limited storage and processing resources of commercially available sensor platforms.