Victor Firoiu

Bio: Victor Firoiu is an academic researcher from Nortel. The author has contributed to research in topics: Queue & Differentiated services. The author has an hindex of 15, co-authored 20 publications receiving 3196 citations.

Modeling TCP Reno performance: a simple model and its empirical validation

Abstract: The steady-state performance of a bulk transfer TCP flow (i.e., a flow with a large amount of data to send, such as FTP transfers) may be characterized by the send rate, which is the amount of data sent by the sender in unit time. In this paper we develop a simple analytic characterization of the steady-state send rate as a function of loss rate and round trip time (RTT) for a bulk transfer TCP flow. Unlike the models of Lakshman and Madhow (see IEE/ACM Trans. Networking, vol.5, p.336-50, 1997), Mahdavi and Floyd (1997), Mathis, Semke, Mahdavi and Ott (see Comput. Commun. Rev., vol.27, no.3, 1997) and by by Ott et al., our model captures not only the behavior of the fast retransmit mechanism but also the effect of the time-out mechanism. Our measurements suggest that this latter behavior is important from a modeling perspective, as almost all of our TCP traces contained more time-out events than fast retransmit events. Our measurements demonstrate that our model is able to more accurately predict TCP send rate and is accurate over a wider range of loss rates. We also present a simple extension of our model to compute the throughput of a bulk transfer TCP flow, which is defined as the amount of data received by the receiver in unit time.

An Expedited Forwarding PHB (Per-Hop Behavior)

Abstract: This document defines a PHB (per-hop behavior) called Expedited Forwarding (EF) The PHB is a basic building block in the Differentiated Services architecture EF is intended to provide a building block for low delay, low jitter and low loss services by ensuring that the EF aggregate is served at a certain configured rate This document obsoletes RFC 2598

A study of active queue management for congestion control

Abstract: In this work, we investigate mechanisms for Internet congestion control in general, and random early detection (RED) in particular. We first study the current proposals for RED implementation and identify several structural problems such as producing large traffic oscillations and introducing unnecessary overhead in the fast path forwarding. We model RED as a feedback control system and discover fundamental laws governing the traffic dynamics in TCP/IP networks. Based on this understanding, we derive a set of recommendations for the architecture and implementation of congestion control modules in routers, such as RED.

Theories and models for Internet quality of service

Abstract: We survey 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 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 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 QoS differentiation without access control, and methods that allow an application to control the performance it receives, in the absence of network support.

A Stochastic Model of TCP Reno Congestion Avoidence and Control

Abstract: The steady state performance of a bulk transfer TCP flow (i.e. a flow with a large amount of data to send, such as FTP transfers) may be characterized by three quantities. The first is the {\em send rate}, which is the amount of data sent by the sender in unit time. The second is the $throughput$, which is the amount of data received by the receiver in unit time. Note that the throughput will always be less than or equal to the send rate due to losses. Finally, the number of non-duplicate packets received by the receiver in unit time give us the $goodput$ of the connection. The goodput is always less than or equal to the throughput, since the receiver may receiver two copies of the same packet due to retransmissions by the sender. In [1] we presented a simple model for predicting the steady state send rate of a bulk transfer TCP flow as a function of loss rate and round trip time. In this paper, we extend that work in two ways. First, we analyze the performance of bulk transfer TCP flows using more precise, stochastic analysis. We show that the predictions of the approximate model in [1] closely match the predictions of the more precise model, thus validating the approximate model. Second, we build upon the analysis in [1] to provide both an approximate formula as well as a more accurate stochastic model for the steady state throughput of a bulk transfer TCP flow. References: [1] J. Padhye, V. Firoiu, D. Towsley and J. Kurose. Modeling TCP Throughput: A Simple Model and its Empirical Validation. In Proccedings of SIGCOMM''98

Network Calculus: A Theory of Deterministic Queuing Systems for the Internet

Abstract: Network Calculus.- Application of Network Calculus to the Internet.- Basic Min-plus and Max-plus Calculus.- Min-plus and Max-plus System Theory.- Optimal Multimedia Smoothing.- FIFO Systems and Aggregate Scheduling.- Adaptive and Packet Scale Rate Guarantees.- Time Varying Shapers.- Systems with Losses.

Fluid-based analysis of a network of AQM routers supporting TCP flows with an application to RED

Abstract: In this paper we use jump process driven Stochastic Differential Equations to model the interactions of a set of TCP flows and Active Queue Management routers in a network setting. We show how the SDEs can be transformed into a set of Ordinary Differential Equations which can be easily solved numerically. Our solution methodology scales well to a large number of flows. As an application, we model and solve a system where RED is the AQM policy. Our results show excellent agreement with those of similar networks simulated using the well known ns simulator. Our model enables us to get an in-depth understanding of the RED algorithm. Using the tools developed in this paper, we present a critical analysis of the RED algorithm. We explain the role played by the RED configuration parameters on the behavior of the algorithm in a network. We point out a flaw in the RED averaging mechanism which we believe is a cause of tuning problems for RED. We believe this modeling/solution methodology has a great potential in analyzing and understanding various network congestion control algorithms.

Modeling TCP Reno performance: a simple model and its empirical validation

Abstract: The steady-state performance of a bulk transfer TCP flow (i.e., a flow with a large amount of data to send, such as FTP transfers) may be characterized by the send rate, which is the amount of data sent by the sender in unit time. In this paper we develop a simple analytic characterization of the steady-state send rate as a function of loss rate and round trip time (RTT) for a bulk transfer TCP flow. Unlike the models of Lakshman and Madhow (see IEE/ACM Trans. Networking, vol.5, p.336-50, 1997), Mahdavi and Floyd (1997), Mathis, Semke, Mahdavi and Ott (see Comput. Commun. Rev., vol.27, no.3, 1997) and by by Ott et al., our model captures not only the behavior of the fast retransmit mechanism but also the effect of the time-out mechanism. Our measurements suggest that this latter behavior is important from a modeling perspective, as almost all of our TCP traces contained more time-out events than fast retransmit events. Our measurements demonstrate that our model is able to more accurately predict TCP send rate and is accurate over a wider range of loss rates. We also present a simple extension of our model to compute the throughput of a bulk transfer TCP flow, which is defined as the amount of data received by the receiver in unit time.

REM: active queue management

Abstract: We describe a new active queue management scheme, random exponential marking (REM), that aims to achieve both high utilization and negligible loss and delay in a simple and scalable manner. The key idea is to decouple the congestion measure from the performance measure such as loss, queue length, or delay. While the congestion measure indicates excess demand for bandwidth and must track the number of users, the performance measure should be stabilized around their targets independent of the number of users. We explain the design rationale behind REM and present simulation results of its performance in wireline and wireless networks.

On designing improved controllers for AQM routers supporting TCP flows

Abstract: In this paper we study a previously developed linearized model of TCP and active queue management (AQM). We use classical control system techniques to develop controllers well suited for the application. The controllers are shown to have better theoretical properties than the well known RED controller. We present guidelines for designing stable controllers subject to network parameters like load level propagation delay etc. We also present simple implementation techniques which require a minimal change to RED implementations. The performance of the controllers are verified and compared with RED using ns simulations. The second of our designs, the proportional integral (PI) controller is shown to outperform RED significantly.