20327349
Analysis and design of the virtual rate control algorithm for stabilizing queues in TCP networks
The virtual rate control (VRC) algorithm has been proposed for active queue management (AQM) in TCP networks. VRC, a rate-based control mechanism, responds quickly to traffic changes, thus allowing for high utilization and small loss. It can effectively stabilize both the input rate and the queue length around their target levels. In this paper, we analyze the stability of the VRC algorithm based on a linearized TCP model with time delay and provide a design guideline for parameter setting to make the overall system stable. Finally, we confirm the validity of our analysis and the effectiveness of VRC compared to RED, PI, REM, and AVQ through extensive ns-2 simulations.
17340710
Stochastic analysis of packet-pair probing for network bandwidth estimation
In this paper, we perform a stochastic analysis of the packet-pair technique, which is a widely used method for estimating the network bandwidth in an end-to-end manner. There has been no explicit delay model of the packet-pair technique primarily because the stochastic behavior of a packet pair has not been fully understood. Our analysis is based on a novel insight that the transient analysis of the G/D/1 system can accurately describe the behavior of a packet pair, providing an explicit stochastic model. We first investigate a single-hop case and derive an analytical relationship between the input and the output probing gaps of a packet pair. Using this single-hop model, we provide a multi-hop model under an assumption of a single tight link. Our model shows the following two important features of the packet-pair technique: (i) The difference between the proposed model and the previous fluid model becomes significant when the input probing gap is around the characteristic value. (ii) The available bandwidth of any link after the tight link is not observable. We verify our model via ns-2 simulations and empirical results. We give a discussion on recent packet-pair models in relation to the proposed model and show that most of them can be regarded as special cases of the proposed model.
9690053
Robust Delay Estimation for Internet Multimedia Applications
Traffic estimation and modeling has been a crucial issue in many research areas of communication networks. For example, intermediate routers in networks estimate the rate of packet flows via queue size information in order to maximize throughput and provide fairness between flows. Also, many senders in the end system such as multi-media applications estimate end-to-end delay between a sender and a receiver to reduce dropping probability of packet. In this position paper, we propose a robust adaptive estimation scheme for Internet multimedia applications. The proposed scheme adopts an autoregressive (AR) model for the process and identifies the parameters of the AR process via a robust identification algorithm. This robust identification algorithm usually leads to better performance when the noise is correlated and/or non-stationary, and it is also more robust to modeling uncertainties. Here, we consider the problem of end-to-end delay estimation for audio playout mechanisms. We rigorously formulate the proposed scheme in the realm of audio playout mechanisms and give some preliminary simulation result which shows effectiveness of the proposed scheme. Even though we apply the proposed scheme to the estimation of end-to-end delay in audio applications, the scheme itself is very general and we expect that it can be applied to many other estimation problems in Internet multimedia applications.
14489739
Robust playout mechanism for Internet audio applications
In Internet audio applications, delay and delay jitter affect mostly the applications' quality of service. Since packet delays are different and changing over time, the receiver needs to buffer some amount of packets before playout. Therefore, the amount of buffered packets and the timing of playout are very important for the performance of applications. We adopt an autoregressive (AR) model for estimation of packet delay and deploy a robust identification algorithm for adjustment of the parameters of the AR process. In our preliminary experiments, this robust algorithm leads to better performance when the noise is correlated and/or non-stationary, and also it is robust to model uncertainties.
16295634
Robust delay estimator for playout buffering in Internet audio applications
In this paper, we propose a robust delay estimation scheme for Internet multimedia applications. The proposed scheme adopts an autoregressive (AR) model for the delay process. The adopted AR model is a natural generalization of the Jacobson's algorithm in TCP retransmission timeout (RTO) estimation. However, unlike fixed parameter values in the Jacobson's algorithm, the parameters of the proposed scheme adapt themselves to the estimation error via a robust identification algorithm. This robust identification algorithm usually leads to better performance when the noise is correlated and/or non-stationary, and it is also more robust to modeling uncertainties. As an application of the proposed algorithm, we consider the problem of delay prediction for audio playout buffering. We rigorously formulate the proposed scheme in the realm of multimedia audio mechanisms and give simulation result which shows its effectiveness.
44748347
A Linear-Time Algorithm for Concave One-Dimensional Dynamic Programming
12402823
A BEM Formulation for Transient Axisymmetric Thermoelastic Analysis Using Particular Integrals
A particular integral formulation is presented for the first time in a purely axisymmetric transient uncoupled thermoelastic analysis. The governing axisymmetric elastostatic equation is used as the complementary solution and the particular integrals for displacements and tractions are derived by integrating the three-dimensional formulation along the circumferential direction leading to elliptic integrals. The numerical results for three example problems are given and compared with their analytical solutions. Generally, the agreement among all of those results is satisfactory, if a few interior points are used to include the known values of temperature.
1974420
Performance evaluation of multiple time scale TCP under self-similar traffic conditions
Measurements of network traffic have shown that self-similarity is a ubiquitous phenomenon spanning across diverse network environments. In previous work, we have explored the feasibility of exploiting long-range correlation structure in self-similar traffic for congestion control. We have advanced the framework of multiple time scale congestion control and shown its effectiveness at enhancing performance for rate-based feedback control. In this article, we extend the multiple time scale control framework to window-based congestion control, in particular, TCP. This is performed by interfacing TCP with a large time scale module that adjusts the aggressiveness of bandwidth consumpton behavior exhibited by TCP as a function of large time scale network state, that is, information that exceeds the time horizon of the feedback loop as determined by RTT. How to effectively utilize such information—due to its probabilistic nature, dispersion over multiple time scales, and realization on top of existing window-based congestion controls—is a nontrivial problem. First, we define a modular extension of TCP (a function call with a simple interface that applies to various flavors of TCP, e.g., Tahoe, Reno, and Vegas) and show that it significantly improves performance. Second, we show that multiple time scale TCP endows the underlying feedback control with proacativity by bridging the uncertainty gap associated with reactive controls which is exacerbated by the high delay-bandwidth product in broadband wide area networks. Third, we investigate the influence of three traffic control dimensions—tracking ability, connection duration, and fairness—on performance. Performance evaluation of multiple time scale TCP is facilitated by a simulation benchmark environment based on physical modeling of self-similar traffic. We explicate our methodology for disc
37635676
Efficient Algorithms for Approximate String Matching with Swaps
Most research on the edit distance problem and thek-differences problem considered the set of edit operations consisting of changes, insertions, and deletions. In this paper we include theswapoperation that interchanges two adjacent characters into the set of allowable edit operations, and we present anO(tmin(m,n))-time algorithm for the extended edit distance problem, wheretis the edit distance between the given strings, and anO(kn)-time algorithm for the extendedk-differences problem. That is, we add swaps into the set of edit operations without increasing the time complexities of previous algorithms that consider only changes, insertions, and deletions for the edit distance andk-differences problems.
9585446
On the performance characteristics of WLANs: revisited
Wide-spread deployment of infrastructure WLANs has made Wi-Fi an integral part of today's Internet access technology. Despite its crucial role in affecting end-to-end performance, past research has focused on MAC protocol enhancement, analysis and simulation-based performance evaluation without sufficient consideration for modeling inaccuracies stemming from inter-layer dependencies, including physical layer diversity, that significantly impact performance. We take a fresh look at IEEE 802.11 WLANs, and using a combination of experiment, simulation, and analysis demonstrate its surprisingly agile performance traits. Our main findings are two-fold. First, contention-based MAC throughput degrades gracefully under congested conditions, enabled by physical layer channel diversity that reduces the effective level of MAC contention. In contrast, fairness and jitter significantly degrade at a critical offered load. This duality obviates the need for link layer flow control for throughput improvement but necessitates traffic control for fairness and QoS. Second, TCP-over-WLAN achieves high throughput commensurate with that of wireline TCP under saturated conditions, challenging the widely held perception that TCP throughput fares poorly over WLANs when subject to heavy contention. We show that TCP-over-WLAN prowess is facilitated by the self-regulating actions of DCF and TCP congestion control that jointly drive the shared physical channel at an effective load of 2--3 wireless stations, even when the number of active stations is very large. Our results highlight subtle inter-layer dependencies including the mitigating influence of TCP-over-WLAN on dynamic rate shifting.