PABO: Mitigating Congestion via Packet Bounce in Data Center Networks

In today's data center, a diverse mix of throughput-sensitive long flows and delay-sensitive short flows are commonly presented in shallow-buffered switches. Long flows could potentially block the transmission of delay-sensitive short flows, leading to degraded performance. Congestion can also be caused by the synchronization of multiple TCP connections for short flows, as typically seen in the partition/aggregate traffic pattern. While multiple end-to-end transport-layer solutions have been proposed, none of them have tackled the real challenge: reliable transmission in the network. In this paper, we fill this gap by presenting PABO -- a novel link-layer design that can mitigate congestion by temporarily bouncing packets to upstream switches. PABO's design fulfills the following goals: i) providing per-flow based flow control on the link layer, ii) handling transient congestion without the intervention of end devices, and iii) gradually back propagating the congestion signal to the source when the network is not capable to handle the congestion.Experiment results show that PABO can provide prominent advantage of mitigating transient congestions and can achieve significant gain on end-to-end delay

Design and analysis of a beacon-less routing protocol for large volume content dissemination in vehicular ad hoc networks

Largevolumecontentdisseminationispursuedbythegrowingnumberofhighquality applications for Vehicular Ad hoc NETworks(VANETs), e.g., the live road surveillance service and the video-based overtaking assistant service. For the highly dynamical vehicular network topology, beacon-less routing protocols have been proven to be efficient in achieving a balance between the system performance and the control overhead. However, to the authors’ best knowledge, the routing design for large volume content has not been well considered in the previous work, which will introduce new challenges, e.g., the enhanced connectivity requirement for a radio link. In this paper, a link Lifetime-aware Beacon-less Routing Protocol (LBRP) is designed for large volume content delivery in VANETs. Each vehicle makes the forwarding decision based on the message header information and its current state, including the speed and position information. A semi-Markov process analytical model is proposed to evaluate the expected delay in constructing one routing path for LBRP. Simulations show that the proposed LBRP scheme outperforms the traditional dissemination protocols in providing a low end-to-end delay. The analytical model is shown to exhibit a good match on the delay estimation with Monte Carlo simulations, as well

Метод описания топологической структуры вычислительных кластеров, основанный на операциях произведений подграфов

Topological structure of communication networks in supercomputers with grow in size and complexity of installation, respectively becomes more difficult. There are many methods to describe it, but such descriptions are cumbersome, which makes them difficult to manipulate. The article proposes an approach to describing the communication environment of a supercomputer, when the communication network is described as a constructor. The elements of the constructor are typical topological structures often found in various computing systems. For this purpose, a language for describing the topological structure has been developed. It based on the operation products of subgraphs. The language is ideologically similar in its principles to the NetML and OMNeT++ languages. Special attention is paid to exceptions in the regularity of networks of real supercomputers; in order to add the possibility of describing this fact, special constructions have been introduced into the language. A library has been developed in the C programming language with purpose to facilitate work with the language intoduced in this article. Also a special wrapper over C library has been written in Python3, which then can be used to visualize graphs described by the language. The expressive power of language has been demonstrated in the description computing clusters: Tianhe-2A, AI Bridging Cloud Infrastructure and Lomonosov-2. The method has been tested and compared with GraphViz DOT it is showed multiple reductions in the Record volume required to save topology for some of the major Top500 systems.Топологическая структура коммуникационных сетей суперкомпьютерных систем при увеличении размера и сложности суперкомпьютеров соответственно усложняется. Для ее описания существует множество методов, однако такие описания являются громоздкими, что усложняет манипулирование ими. В статье предложен подход к описанию коммуникационной среды суперкомпьютера, когда коммуникационная сеть описывается как конструктор, где элементами конструктора являются типовые топологические структуры, часто встречающиеся в различных вычислительных системах. С этой целью разработан язык описания топологической структуры, основанный на операции произведения подграфов. Язык идейно схож в своих принципах с языками NetML и OMNeT++. Отдельное внимание в работе уделяется исключениям в регулярности сетей реальных суперкомпьютеров; с целью добавления возможности описания данного факта в язык внесены специальные конструкции. Для поддержки работы с языком описания разработана библиотека на языке программирования Си и специальная оболочка над ней написанная на языке Python3, которая затем может использоваться для визуализации описываемых языком графов. Выразительная мощность языка была продемонстрирована на описании вычислительных кластеров: Tianhe-2A, AI Bridging Cloud Infrastructure и Ломоносов-2. Метод был проверен и сравнен с GraphViz DOT показано многократное сокращение необходимых объема записи для некоторых крупных систем из Top500

Saving Energy in Mobile Devices for On-Demand Multimedia Streaming -- A Cross-Layer Approach

This paper proposes a novel energy-efficient multimedia delivery system called EStreamer. First, we study the relationship between buffer size at the client, burst-shaped TCP-based multimedia traffic, and energy consumption of wireless network interfaces in smartphones. Based on the study, we design and implement EStreamer for constant bit rate and rate-adaptive streaming. EStreamer can improve battery lifetime by 3x, 1.5x and 2x while streaming over Wi-Fi, 3G and 4G respectively.Comment: Accepted in ACM Transactions on Multimedia Computing, Communications and Applications (ACM TOMCCAP), November 201

A Comparative Study of Wireless Sensor Networks and Their Routing Protocols

Recent developments in the area of micro-sensor devices have accelerated advances in the sensor networks field leading to many new protocols specifically designed for wireless sensor networks (WSNs). Wireless sensor networks with hundreds to thousands of sensor nodes can gather information from an unattended location and transmit the gathered data to a particular user, depending on the application. These sensor nodes have some constraints due to their limited energy, storage capacity and computing power. Data are routed from one node to other using different routing protocols. There are a number of routing protocols for wireless sensor networks. In this review article, we discuss the architecture of wireless sensor networks. Further, we categorize the routing protocols according to some key factors and summarize their mode of operation. Finally, we provide a comparative study on these various protocols

A Survey of Coverage Problems in Wireless Sensor Networks

Coverage problem is an important issue in wireless sensor networks, which has a great impact on the performance of wireless sensor networks. Given a sensor network, the coverage problem is to determine how well the sensing field is monitored or tracked by sensors. In this paper, we classify the coverage problem into three categories: area coverage, target coverage, and barrier coverage, give detailed description of different algorithms belong to these three categories. Moreover, we specify the advantages and disadvantages of the existing classic algorithms, which can give a useful direction in this area

Cybersecurity in Power Grids: Challenges and Opportunities

Increasing volatilities within power transmission and distribution force power grid operators to amplify their use of communication infrastructure to monitor and control their grid. The resulting increase in communication creates a larger attack surface for malicious actors. Indeed, cyber attacks on power grids have already succeeded in causing temporary, large-scale blackouts in the recent past. In this paper, we analyze the communication infrastructure of power grids to derive resulting fundamental challenges of power grids with respect to cybersecurity. Based on these challenges, we identify a broad set of resulting attack vectors and attack scenarios that threaten the security of power grids. To address these challenges, we propose to rely on a defense-in-depth strategy, which encompasses measures for (i) device and application security, (ii) network security, and (iii) physical security, as well as (iv) policies, procedures, and awareness. For each of these categories, we distill and discuss a comprehensive set of state-of-the art approaches, as well as identify further opportunities to strengthen cybersecurity in interconnected power grids