Insights into the Design of Congestion Control Protocols for Multi-Hop Wireless Mesh Networks

The widespread deployment of multi-hop wireless mesh networks will depend on the performance seen by the user. Unfortunately, the most predominant transport protocol, TCP, performs poorly over such networks, even leading to starvation in some topologies. In this work, we characterize the root causes of starvation in 802.11 scheduled multi-hop wireless networks via simulations. We analyze the performance of three categories of transport protocols. (1) end-to-end protocols that require implicit feedback (TCP SACK), (2) Explicit feedback based protocols (XCP and VCP) and (3) Open-loop protocol (UDP). We ask and answer the following questions in relation to these protocols: (a) Why does starvation occur in different topologies? Is it intrinsic to TCP or, in general, to feedback-based protocols? or does it also occur in the case of open-loop transfers such as CBR over UDP? (a) What is the role of application behavior on transport layer performance in multi-hop wireless mesh networks? (b) Is sharing congestion in the wireless neighborhood essential for avoiding starvation? (c) For explicit feedback based transport protocols, such as XCP and VCP, what performance can be expected when their capacity estimate is inaccurate? Based on the insights derived from the above analysis, we design a rate-based protocol called VRate that uses the two ECN bits for conveying load feedback information. VRate achieves near optimal rates when configured with the correct capacity estimate

REPP-H: runtime estimation of power and performance on heterogeneous data centers

Modern data centers increasingly demand improved performance with minimal power consumption. Managing the power and performance requirements of the applications is challenging because these data centers, incidentally or intentionally, have to deal with server architecture heterogeneity [19], [22]. One critical challenge that data centers have to face is how to manage system power and performance given the different application behavior across multiple different architectures.This work has been supported by the EU FP7 program (Mont-Blanc 2, ICT-610402), by the Ministerio de Economia (CAP-VII, TIN2015-65316-P), and the Generalitat de Catalunya (MPEXPAR, 2014-SGR-1051). The material herein is based in part upon work supported by the US NSF, grant numbers ACI-1535232 and CNS-1305220.Peer ReviewedPostprint (author's final draft

Flying real-time network to coordinate disaster relief activities in urban areas

While there have been important advances within wireless communication technology, the provision of communication support during disaster relief activities remains an open issue. The literature in disaster research reports several major restrictions to conducting first response activities in urban areas, given the limitations of telephone networks and radio systems to provide digital communication in the field. In search-and-rescue operations, the communication requirements are increased, since the first responders need to rely on real-time and reliable communication to perform their activities and coordinate their efforts with other teams. Therefore, these limitations open the door to improvisation during disaster relief efforts. In this paper, we argue that flying ad-hoc networks can provide the communication support needed in these scenarios, and propose a new solution towards that goal. The proposal involves the use of flying witness units, implemented using drones, that act as communication gateways between first responders working at different locations of the affected area. The proposal is named the Flying Real-Time Network, and its feasibility to provide communication in a disaster scenario is shown by presenting both a real-time schedulability analysis of message delivery, as well as simulations of the communication support in a physical scenario inspired by a real incident. The obtained results were highly positive and consistent, therefore this proposal represents a step forward towards the solution of this open issuePeer ReviewedPostprint (published version

Mechanisms for System-Level Fault Tolerance in Real-Time Systems

this paper we concentrate on the development of a method for achieving fault tolerance at the system level, and we define a mechanism by which the guarantees of applications accepted for execution may be revoked. The removal of applications from, or the their replacement in, a schedule may be necessary in order to maintain the system in a safe state, even in a real-time environment. Our scheme encompasses recovery techniques such as graceful degradation, load shedding, and reconfiguration, while the implementation is done transparently to the user. The paper is organized as follows. In the rest of this section we give a brief overview of previous work in the field, as well as of the framework we are working with. In the following section we define the basic way to treat faults at the system level, called scenario changes. In Section 2.2 we describe the mechanisms and conditions necessary to apply the scenario changes, and in Section 3 we describe practical uses for the scheme. We close the paper with concluding remarks and directions for future work

Efficient scheduling for sensor networks

Abstract — Sensor networks opened new opportunities to monitor the environment. In order to retrieve the desired data, sensors are usually organized into a hierarchy and synchronize when transmitting the data towards the base station. Many scheduling schemes have been proposed with the goal of allowing sensors to sleep as much as possible and ultimately save energy. In this paper, we propose two new scheduling algorithms that assign predefined slots to each sensor. These algorithms are distributed, need very little global information and do not need knowledge about the location of sensors or the network topology. As others, we also assume that loose clock synchronization is available. The experimental results confirm our expectations. They show a significant reduction in the average time awake per node of at least three times compared to more traditional routin