Theories and Models for Internet Quality of Service

We survey recent advances in theories and models for Internet Quality of Service (QoS). We start with the theory of network calculus, which lays the foundation for support of deterministic performance guarantees in networks, and illustrate its applications to integrated services, differentiated services, and streaming media playback delays. We also present mechanisms and architecture for scalable support of guaranteed services in the Internet, based on the concept of a stateless core. Methods for scalable control operations are also briefly discussed. We then turn our attention to statistical performance guarantees, and describe several new probabilistic results that can be used for a statistical dimensioning of differentiated services. Lastly, we review recent proposals and results in supporting performance guarantees in a best effort context. These include models for elastic throughput guarantees based on TCP performance modeling, techniques for some quality of service differentiation without access control, and methods that allow an application to control the performance it receives, in the absence of network support

Advances in Internet Quality of Service

We describe recent advances in theories and architecture that support performance guarantees needed for quality of service networks. We start with deterministic computations and give applications to integrated services, differentiated services, and playback delays. We review the methods used for obtaining a scalable integrated services support, based on the concept of a stateless core. New probabilistic results that can be used for a statistical dimensioning of differentiated services are explained; some are based on classical queuing theory, while others capitalize on the deterministic results. Then we discuss performance guarantees in a best effort context; we review: methods to provide some quality of service in a pure best effort environment; methods to provide some quality of service differentiation without access control, and methods that allow an application to control the performance it receives, in the absence of network support

Packet Scale Rate Guarantee for non-FIFO Nodes

Packet Scale Rate Guarantee (PSRG) is a generic node model which underlies the definition of Expedited Forwarding (EF) proposed in the context of Internet Differentiated Services. For the case of FIFO nodes, PSRG is equivalent to the well-understood concept of adaptive service curve. However, in practice, many devices do not necessarily preserve the FIFO property, and therefore known FIFO results do not hold. This paper analyzes the properties of PSRG in the absence of FIFO assumption. Our analysis is based on a novel characterization of PSRG which avoids the use of virtual finish times; it is obtained by min-max algebra. We use it to show that delay bounds previously obtained for the FIFO case are still valid; in contrast, we find that this is not true for the characterization of the concatenation of two nodes

Modelagem de desempenho de servidores Web empregando a teoria Network Calculus

Orientadora: Cristina Duarte MurtaDissertaçao (mestrado) - Universidade Federal do Paraná, Setor de Ciencias Exatas, Programa de Pós-Graduaçao em Informática. Defesa: Curitiba, 2005Inclui bibliografiaResumo: Network Calculus 'e uma teoria que modela o desempenho de sistemas de filas e permite o c'alculo de limites determin'?sticos de desempenho, quando os fluxos de entrada obedecem a certas restri¸c˜oes. Este trabalho descreve a aplica¸c˜ao desta teoria para a modelagem de desempenho de servidores Web. O desempenho dos servidores Web 'e vital para o sucesso de muitas organiza¸c˜oes. Acompanhar, avaliar e modelar o desempenho dos servidores Web s˜ao tarefas fundamentais para prover acesso eficiente e confi'avel, em especial no caso de servidores populares e eventualmente sobrecarregados. Diferentes t'ecnicas est˜ao dispon'?veis para a avalia¸c˜ao de desempenho de um sistema. Cada uma apresenta possibilidades, vantagens e limita¸c˜oes e 'e aplic'avel em diferentes contextos e com custos diversos. Assim, estudar as possibilidades de aplica¸c˜ao de uma nova teoria para modelagem de desempenho de um sistema como os servidores Web 'e uma tarefa importante. Para demonstrar a aplica¸c˜ao da teoria e seus resultados em servidores Web, as fun¸c˜oes que descrevem os resultados do Network Calculus, que s˜ao fun¸c˜oes descritas na 'algebra min-plus, foram implementadas e testadas com registros de acesso de alguns servidores Web. Os principais resultados da teoria, a saber, o limite de atraso, o limite do tamanho da fila e o limite do fluxo de sa'?da, foram obtidos e s˜ao apresentados para os servidores em quest˜ao. Outros aspectos tamb'em discutidos s˜ao a compara¸c˜ao com a an'alise operacional, a aplica¸c˜ao da teoria para modelar controle de admiss˜ao e a complexidade computacional das fun¸c˜oes implementadas.Abstract: Network Calculus is a theory that models the perfomance of queueing systems. It provides deterministic bounds on performance, when the input flows obey certain restrictions. This work describes the application of this theory for the performance modeling of Web servers. The performance of Web servers is vital for the success of many organizations. To manage, evaluate and model the performance of Web servers are basic tasks to provide efficient and trustworthy access, in special in the case of popular and eventually overloaded servers. Different techniques are available for the performance evaluation of a system. Each one presents possibilities, advantages and limitations. The application of a new theory for modeling of performance of a system such as Web servers is an important task. To demostrate the application of the theory and its results in Web servers, the functions that describe the results of Network Calculus, which are described in min-plus algebra, have been implemented and tested with traces of some Web servers. The main results of the theory, which are the delay bound, the backlog bound and the output flow had been gotten and are presented for the servers considered. Other aspects of the theory also argued are the comparison with the operational analysis, the application of the theory to model admission control and the analysis of the computational complexity of the implemented functions

Bits of Internet traffic control

In this work, we consider four problems in the context of Internet traffic control. The first problem is to understand when and why a sender that implements an equation-based rate control would be TCP-friendly, or not—a sender is said to be TCP-friendly if, under the same operating conditions, its long-term average send rate does not exceed that of a TCP sender. It is an established axiom that some senders in the Internet would need to be TCP-friendly. An equation-based rate control sender plugs-in some on-line estimates of the loss-event rate and an expected round-trip time in a TCP throughput formula, and then at some points in time sets its send rate to such computed values. Conventional wisdom held that if a sender adjusts its send rate as just described, then it would be TCP-friendly. We show exact analysis that tells us when we should expect an equation-based rate control to be TCP-friendly, and in some cases excessively so. We show experimental evidence and identify the causes that, in a realistic scenario, make an equation-based rate control grossly non-TCP-friendly. Our second problem is to understand the throughput achieved by another family of send rate controls—we termed these "increase-decrease controls," with additive-increase/multiplicative-decrease as a special case. One issue that we consider is the allocation of long-term average send rates among senders that adjust their send rates by an additive-increase/multiplicative-decrease control, in a network of links with arbitrary fixed routes, and arbitrary round-trip times. We show what the resulting send rate allocation is. This result advances the state-of-the-art in understanding the fairness of the rate allocation in presence of arbitrary round-trip times. We also consider the design of an increase-decrease control to achieve a given target loss-throughput function. We show that if we design some increase-decrease controls under a commonly used reference loss process—a sequence of constant inter-loss event times—then we know that these controls would overshoot their target loss-throughput function, for some more general loss processes. A reason to study the design problem is to construct an increase-decrease control that would be friendly to some other control, TCP, for instance. The third problem that we consider is how to obtain probabilistic bounds on performance for nodes that conform to the per-hop-behavior of Expedited Forwarding, a service of differentiated services Internet. Under the assumption that the arrival process to a node consists of flows that are individually regulated (as it is commonplace with Expedited Forwarding) and the flows are stochastically independent, we obtained probabilistic bounds on backlog, delay, and loss. We apply our single-node performance bounds to a network of nodes. Having good probabilistic bounds on the performance of nodes that conform to the per-hop-behavior of Expedited Forwarding, would enable a dimensioning of those networks more effectively, than by using some deterministic worst-case performance bounds. Our last problem is on the latency of an input-queued switch that implements a decomposition-based scheduler. With decomposition-based schedulers, we are given a rate demand matrix to be offered by a switch in the long-term between the switch input/output port pairs. A given rate demand matrix is, by some standard techniques, decomposed into a set of permutation matrices that define the connectivity of the input/output port pairs. The problem is how to construct a schedule of the permutation matrices such that the schedule offers a small latency for each input/output port pair of the switch. We obtain bounds on the latency for some schedulers that are in many situations smaller than a best-known bound. It is important to be able to design switches with bounds on their latencies in order to provide guarantees on delay-jitter