Roberta Fracchia

A WiSE extension of SCTP for wireless networks

This paper presents WiSE, a transport-layer protocol that modifies the standard SCTP protocol. WiSE aims at exploiting SCTPs multihoming capabilities by selecting in real time the best choice among available, alternate paths to the same destination. Through the use of bandwidth estimation techniques, WiSE tries to infer whether losses are due to congestion or radio channel errors. At the same time, the available bandwidth on the current path used for transmission is matched to that of an alternate path, also probed for available bandwidth; if the current path is severely congested, and the alternate path is lightly loaded, WiSE switches the transmission onto the alternate path, using SCTPs flexible path management capabilities. Extensive simulations under different scenarios highlight the superiority of the proposed solution with respect to the standard SCTP implementation.

Autonomic Interface Selection for Mobile Wireless Users

We address the problem of self-configuration of user stations in a wireless environment with overlapping coverages. We propose and investigate a solution operating on top of the transport layer [called Autonomic Interface SeLEction (AISLE)] that exploits nodes featuring multihoming capabilities, i.e., with more than one network interface. Our solution is independent of the technology used at the physical and medium access control (MAC) layers. To evaluate the performance of AISLE, we first analytically derive the optimal way in which mobile stations should partition across multiple overlapping wireless networks, and we then verify through simulation the AISLE ability to achieve the optimal station partitioning. Different scenarios are considered, which include the case of heterogeneous networks, such as 802.11 wireless local area networks (WLANs) and third-generation (3G) cellular networks, with stations moving across an area with different degrees of overlapping coverages, as well as the case of heterogeneous stations, in which only some stations adopt AISLE.

VANETs: Why Use Beaconing at All ?

We investigate the broadcast problem in intervehicular networks, aiming at assessing a definitive comparison of two antipodean algorithm classes: the first one makes use of instantaneous information, while the second one relies on longer- term knowledge gained through a beaconing procedure. Using a realistic microscopic model to represent the vehicular traffic flow, we investigate the performance of the above broadcast algorithm classes by simulation. In order to explore a very large algorithmic design space, we devise a Convex Hull framework that allows us to effectively compare and compactly present the boundaries of the solution space for each algorithm class. By the use of such framework we show that the beaconing approach is not justified for broadcast in suburban and highway VANETs, as there is no performance gain that justifies the complexity entailed by the beaconing procedure.

Knowing vehicles location HELPS avoiding broadcast packets storm

This paper proposes HELP, a simple and distributed broadcast algorithm for warning delivery services in inter-vehicular ad hoc networks. Assuming that neighborhood location information is available from the routing layer, each node determines whether to re-broadcast the message based on i) the coverage zone of the received message and ii) the estimated position of its neighbors. Investigations are led using a popular microscopic traffic model, in order to ensure realism of the networking performance evaluation. Results show that the algorithm efficiently limits the number of broadcasted messages, which is very close to the optimal. Furthermore, robustness of the results in terms of the number of informed vehicles can also be achieved, provided that a safety error margin is considered in the position estimate

AISLE: autonomic interface selection for wireless users

We address the problem of wireless stations self-configuration in a WLAN environment with overlapping access point coverages. We propose and investigate a transport-layer solution called AISLE (autonomic interface selection) that builds on top of the SCTP protocol and exploits its multihoming features. Through simulation, we evaluate AISLEs capability to maximize the throughput of multi-interface stations and to achieve an optimal partition of the stations across overlapping WLANs. Although we focus on a WLAN scenario, AISLE is independent of the technology used at the physical and MAC layers

Alert service in VANET: Analysis and design

This paper focuses on inter-vehicular networks providing warning delivery service. As soon as a danger is detected, the propagation of a warning message is triggered, with the aim of guaranteeing a safety area around the point in which the danger is located. The service is based on multi-hop ad hoc inter-vehicular communications with a probabilistic choice of the relay nodes. The scenario we consider consists of high speed streets, such as highways, in which vehicles exhibit one-dimensional movements along the direction of the road. We propose an analytical model for the study of this service and derive performance indices such as the probability that a vehicle is informed, and the average number of duplicate messages received by a vehicle. Moreover, we use the model to discuss system design issues, which include the proper setting of the flooding probability at each vehicle so that a given probability to receive the warning can be guaranteed to all vehicles in the safety area around the danger point. The model is validated against simulation results and, thanks to the high level of accuracy, can be instrumental to the performance evaluation and design of broadcasting techniques in inter-vehicular networks.

On the quality of broadcast services in vehicular ad hoc networks

We investigate the broadcast problem in suburban and highway inter-vehicular networks, aiming at providing a definitive comparison of two antipodean broadcast algorithm classes: the first one makes use of some instantaneous information locally available at the vehicles (such as vehicle position and speed), while the second one relies on long-term knowledge gained through a beaconing procedure. Using a realistic microscopic model to represent the vehicular traffic flow, we investigate the performance of the above broadcast algorithm classes by simulation, considering different classes of network services (e.g., Critical, Normal, and Low-priority). In order to explore a very large algorithmic design space, we devise a convex hull framework that allows us to effectively compare and compactly present the boundaries of the solution space for each algorithm class. By the use of such framework, we show that the beaconless performance encompasses a wider spectrum with respect to the beaconed one, with lower complexity and overhead. Copyright

A Queueing Network Model of Short-Lived TCP Flows with Mixed Wired and Wireless Access Links

We present an analytical model, based on a Fixed Point Approximation (FPA) solution, that can be used to derive the performance of different sets of TCP connections that share, and compete for, a common resource, typically a link and its associated buffer. A set of TCP connections is a group of connections that can be considered homogeneous, e.g., they have similar RTTs and all have a wireless access. TCP connections are modeled through the OMQN (Open Multiclass Queueing Network) paradigm. The conditions that define the feasibility of the solution and allow the convergence of the model are discussed and an application example with a RED buffer where wired and wireless connections converge is presented.