TCP smart framing: a segmentation algorithm to reduce TCP latency

TCP Smart Framing, or TCP-SF for short, enables the Fast Retransmit/Recovery algorithms even when the congestion window is small. Without modifying the TCP congestion control based on the additive-increase/multiplicative-decrease paradigm, TCP-SF adopts a novel segmentation algorithm: while Classic TCP always tries to send full-sized segments, a TCP-SF source adopts a more flexible segmentation algorithm to try and always have a number of in-flight segments larger than 3 so as to enable Fast Recovery. We motivate this choice by real traffic measurements, which indicate that today's traffic is populated by short-lived flows, whose only means to recover from a packet loss is by triggering a Retransmission Timeout. The key idea of TCP-SF can be implemented on top of any TCP flavor, from Tahoe to SACK, and requires modifications to the server TCP stack only, and can be easily coupled with recent TCP enhancements. The performance of the proposed TCP modification were studied by means of simulations, live measurements and an analytical model. In addition, the analytical model we have devised has a general scope, making it a valid tool for TCP performance evaluation in the small window region. Improvements are remarkable under several buffer management schemes, and maximized by byte-oriented schemes

Let Your Reputation Precede You

Although Vehicular Networks are still on the drawing board, the recent announcement by the NHTSA that they will begin working on regulations for V2V (Vehicle-to- Vehicle) communication has spurred concerns that more and more personal data may be unduly disseminated as we drive our cars. We examine a scenario where vehicles use anonymous certificates, provided by a central authority, and do not divulge their position (e.g., for the purpose of accident prevention), but merely exchange contextual traffic information (congestion, roadworks, accidents in the area...). The reliability of such information is corroborated by the vehicle reputation, assigned by a Central Controller (CC). The mechanisms that lead to the forming of vehicle reputation are outside the scope of this paper. We are instead interested in designing a system for the robust dissemination of reputation and in understanding its implications on user privacy

Optimal Content Downloading in Vehicular Networks

We consider a system where users aboard communication-enabled vehicles are interested in downloading different contents from Internet-based servers. This scenario captures many of the infotainment services that vehicular communication is envisioned to enable, including news reporting, navigation maps and software updating, or multimedia file downloading. In this paper, we outline the performance limits of such a vehicular content downloading system by modelling the downloading process as an optimization problem, and maximizing the overall system throughput. Our approach allows us to investigate the impact of different factors, such as the roadside infrastructure deployment, the vehicle-to-vehicle relaying, and the penetration rate of the communication technology, even in presence of large instances of the problem. Results highlight the existence of two operational regimes at different penetration rates and the importance of an efficient, yet 2-hop constrained, vehicle-to-vehicle relaying

A Simulation Study of Web Traffic over DiffServ Networks

We present a simulation study of HTTP traffic crossing a DiffServ domain. We consider both the cases where the reserved bandwidth is not exceeded by the offered traffic (overprovisioning) and where the assured traffic competes with the classic best effort class (underprovisioning). The reported simulation shows that the DiffServ approach is able to protect the assured flows in the first case, while the performance benefits are tighter in the second case, in which fairness issues arise between long and short-lived flows

Persistent Localized Broadcasting in VANETs

We present a communication protocol, called LINGER, for persistent dissemination of delay-tolerant information to vehicular users, within a geographical area of interest. The goal of LINGER is to dispatch and confine information in localized areas of a mobile network with minimal protocol overhead and without requiring knowledge of the vehicles' routes or destinations. LINGER does not require roadside infrastructure support: it selects mobile nodes in a distributed, cooperative way and lets them act as "information bearers", providing uninterrupted information availability within a desired region. We analyze the performance of our dissemination mechanism through extensive simulations, in complex vehicular scenarios with realistic node mobility. The results demonstrate that LINGER represents a viable, appealing alternative to infrastructure-based solutions, as it can successfully drive the information toward a region of interest from a far away source and keep it local with negligible overhead. We show the effectiveness of such an approach in the support of localized broadcasting, in terms of both percentage of informed vehicles and information delivery delay, and we compare its performance to that of a dedicated, state-of-the-art protoco

User Patience and the Web: a hands-on investigation

We present a study of Web user behavior when network performance decreases causing an increase of page transfer times. Real traffic measurements are analyzed to infer whether worsening network conditions translate into greater impatience by the user, which translates in early interruption of TCP connections. Several parameters are studied in order to gather their impact on the interruption probability on Web transfers: time of day, file size, throughput and time elapsed since the beginning of the download. From the results presented, we try to paint a picture of the complex interactions between user perception of the Web and network-level events