Minimally-intrusive frequent round trip time measurements using Synthetic Packet-Pairs

Accurate and frequent round trip time (RTT) measurements are important in testbeds and operational networks. Active measurement techniques inject probe packets that may modify the behaviour of the observed network and may produce misleading RTT estimates if the network handles probe packets differently to regular packets. Previous passive measurement techniques address these issues, but require precise time synchronisation or are limited to certain traffic types. We introduce Synthetic Packet-Pairs (SPP), a novel passive technique for RTT measurement. SPP provides frequently updated RTT measurements using any network traffic already present in the network without the need for time synchronisation. SPP accurately measures the RTT experienced by any application's traffic, even applications that do not exhibit symmetric client-server packet exchanges. We experimentally demonstrate the advantages of SPP

Every timestamp counts: accurate tracking of network latencies using reconcilable difference aggregator

IEEE User-facing services deployed in data centers must respond quickly to user actions. The measurement of network latencies is of paramount importance. Recently, a new family of compact data structures has been proposed to estimate one-way latencies. In order to achieve scalability, these new methods rely on timestamp aggregation. Unfortunately, this approach suffers from serious accuracy problems in the presence of packet loss and reordering, given that a single lost or out-of-order packet may invalidate a huge number of aggregated samples. In this paper, we unify the problem to detect lost and reordered packets within the set reconciliation framework. Although the set reconciliation approach and the data structures for aggregating packet timestamps are previously known, the combination of these two principles is novel. We present a space-efficient synopsis called reconcilable difference aggregator (RDA). RDA maximizes the percentage of useful packets for latency measurement by mapping packets to multiple banks and repairing aggregated samples that have been damaged by lost and reordered packets. RDA simultaneously obtains the average and the standard deviation of the latency. We provide a formal guarantee of the performance and derive optimized parameters. We further design and implement a user-space passive latency measurement system that addresses practical issues of integrating RDA into the network stack. Our extensive evaluation shows that compared with existing methods, our approach improves the relative error of the average latency estimation in 10-15 orders of magnitude, and the relative error of the standard deviation in 0.5-6 orders of magnitude.Peer ReviewedPostprint (author's final draft

A modular traffic sampling architecture for flexible network measurements

Dissertação de Mestrado (Programa Doutoral em Informática)The massive traffic volumes and the heterogeneity of services in today’s networks urge for flexible, yet simple measurement solutions to assist network management tasks, without impairing network performance. To turn treatable tasks requiring traffic analysis, sampling the traffic has become mandatory, triggering substantial research in the area. In fact, multiple sampling techniques have been proposed to assist network engineering tasks, each one targeting specific measurement goals and traffic scenarios. Despite that, there is still a lack of an encompassing solution able to support the flexible deployment of these techniques in production networks. In this context, this research work proposes a modular traffic sampling architecture able to foster the flexible design and deployment of efficient measurement strategies. The architecture is composed of three layers i.e., management plane, control plane and data plane covering key components to achieve versatile and lightweight measurements in diverse traffic scenarios and measurement activities. The flexibility and modularity in deploying different sampling strategies relies upon a novel taxonomy of sampling techniques, in which, current and emerging techniques are identified regarding their inner characteristics - granularity, selection trigger and selection scheme. Following the proposed taxonomy, a sampling framework prototype has been developed and used as an experimental implementation of the proposed architecture, providing a fair environment to assess and compare sampling techniques under distinct measurement scenarios. Supported by the sampling framework, distinct techniques have been evaluated regarding their performance in balancing the computational burden and the accuracy in supporting traffic workload estimation and flow analysis. The results have demonstrated the relevance and applicability of the proposed architecture, revealing that a modular and configurable approach to sampling is a step forward for improving sampling scope and efficiency.Os grandes volumes de tráfego e a heterogeneidade de serviços nas redes atuais requerem soluções de medição que sejam flexíveis e simples de modo a sustentar as tarefas de gestão de redes sem afetar o desempenho das mesmas. Para tornar tratável as tarefas que exigem análise de tráfego, tornou-se obrigatório recorrer a amostragem do tráfego, motivando uma investigação substancial na área. Como consequência, várias técnicas de amostragem foram propostas para auxiliar as tarefas de engenharia de redes, cada uma orientada a satisfazer objetivos de medição e cenários de tráfego específicos. Apesar disso, ainda não existe uma solução abrangente capaz de suportar a implantação flexível destas técnicas em redes de produção. Neste contexto, este trabalho propõe uma arquitetura modular de amostragem de tráfego capaz de fomentar a concepção flexível e a implementação de estratégias efi- cientes de medição de tráfego. A arquitetura é composta por três camadas, nomeadamente, camada de gestão, camada de controle e camada de dados, cobrindo os principais componentes para alcançar versatilidade e baixo custo computacional em variados cenários de tráfego e atividades de medição. A flexibilidade e modularidade na implementação de diferentes técnicas de amostragem baseia-se numa nova taxonomia, na qual técnicas atuais e emergentes são identificadas de acordo com suas características internas - granularidade, trigger de seleção e esquema de seleção. Seguindo a taxonomia proposta, um protótipo estruturando e agregando as diferentes técnicas de amostragem foi desenvolvido e utilizado na implementação experimental da arquitetura, permitindo avaliar e comparar as técnicas de amostragem em diversos cenários de medição. Suportado pelo protótipo desenvolvido, distintas técnicas foram avaliadas quanto ao seu desempenho em equilibrar a carga computacional e a acurácia na estimação do volume de tráfego e na análise de fluxos. Os resultados demonstraram a relevância e aplicabilidade da arquitetura de amostragem proposta, revelando que uma abordagem modular e configurável constitui um avanço no sentido de melhorar a eficiência na amostragem de tráfego

JTP, an energy-aware transport protocol for mobile ad hoc networks (PhD thesis)

Wireless ad-hoc networks are based on a cooperative communication model, where all nodes not only generate traffic but also help to route traffic from other nodes to its final destination. In such an environment where there is no infrastructure support the lifetime of the network is tightly coupled with the lifetime of individual nodes. Most of the devices that form such networks are battery-operated, and thus it becomes important to conserve energy so as to maximize the lifetime of a node. In this thesis, we present JTP, a new energy-aware transport protocol, whose goal is to reduce power consumption without compromising delivery requirements of applications. JTP has been implemented within the JAVeLEN system. JAVeLEN [RKM+08], is a new system architecture for ad hoc networks that has been developed to elevate energy efficiency as a first-class optimization metric at all protocol layers, from physical to transport. Thus, energy gains obtained in one layer would not be offset by incompatibilities and/or inefficiencies in other layers. To meet its goal of energy efficiency, JTP (1) contains mechanisms to balance end-toend vs. local retransmissions; (2) minimizes acknowledgment traffic using receiver regulated rate-based flow control combined with selected acknowledgments and in-network caching of packets; and (3) aggressively seeks to avoid any congestion-based packet loss. Within this ultra low-power multi-hop wireless network system, simulations and experimental results demonstrate that our transport protocol meets its goal of preserving the energy efficiency of the underlying network. JTP has been implemented on the actual JAVeLEN nodes and its benefits have been demonstrated on a real system

JTP, an energy-aware transport protocol for mobile ad hoc networks

Wireless ad-hoc networks are based on a cooperative communication model, where all nodes not only generate traffic but also help to route traffic from other nodes to its final destination. In such an environment where there is no infrastructure support the lifetime of the network is tightly coupled with the lifetime of individual nodes. Most of the devices that form such networks are battery-operated, and thus it becomes important to conserve energy so as to maximize the lifetime of a node. In this thesis, we present JTP, a new energy-aware transport protocol, whose goal is to reduce power consumption without compromising delivery requirements of applications. JTP has been implemented within the JAVeLEN system. JAVeLEN~\cite{javelen08redi}, is a new system architecture for ad hoc networks that has been developed to elevate energy efficiency as a first-class optimization metric at all protocol layers, from physical to transport. Thus, energy gains obtained in one layer would not be offset by incompatibilities and/or inefficiencies in other layers. To meet its goal of energy efficiency, JTP (1) contains mechanisms to balance end-to-end vs. local retransmissions; (2) minimizes acknowledgment traffic using receiver regulated rate-based flow control combined with selected acknowledgments and in-network caching of packets; and (3) aggressively seeks to avoid any congestion-based packet loss. Within this ultra low-power multi-hop wireless network system, simulations and experimental results demonstrate that our transport protocol meets its goal of preserving the energy efficiency of the underlying network. JTP has been implemented on the actual JAVeLEN nodes and its benefits have been demoed on a real system

Empirical evaluation of hash functions for PacketID generation in sampled multipoint measurements

A broad spectrum of network measurement applications demand for multipoint, measurements; e.g. one-way delay measurements or packets path tracing. A passive multipoint measurement, technique is realized by generating a timestamp and a packet identifier (1D) for each packet traversing an observation point and sending this information to a collector. The packet 1D can be provided by using parts of the packet, or generating a digest, of the packet, content. Multipoint, measurements demand for high resource measurement infrastructure. Random packet, selection techniques can reduce the resource consumption while still maintaining sufficient information about most metrics. Nevertheless random packet, selection cannot, be used for multipoint measurements, because the packets selection decisions on its path can differ. Hash-based selection is a deterministic passive multipoint measurement technique that emulates random selection and enables the correlation of a selected subset of packets at, different, measurement, points. The selection decision is based on a hash value over invariant parts of the packet. When hash-based selection is applied two hash values are generated - one on which the selection decision is based and a second one that, is used m the packet 1D. In a previous paper we already evaluated hash functions for hash-based selection. In this paper we analyze hi hash functions for packet 1D generation. Other authors recommend the use of two different hash values for both operations - we show that in certain scenarios it is more efficient to use only one hash value