Additive-increase Multiplicative-decrease Congestion Research Articles

A performance comparison of hose rate controller approaches for P2P-TV applications

The goal of this paper is to investigate rate control mechanisms for unstructured P2P-TV applications adopting UDP as transport protocol. We focus on a novel class of Hose Rate Controllers (HRC), which aim at regulating the aggregate upload rate of each peer. This choice is motivated by the peculiar P2P-TV needs: video content is not elastic but it is subject to real-time constraints, so that the epidemic chunk exchange mechanism is much more bursty for P2P-TV than file sharing applications. Furthermore, the peer up-link (e.g., ADSL/Cable) is typically the shared for flows in real scenarios. We compare two classes of aggregate rate control mechanisms: Delay Based (DB) less-than-best-effort mechanisms, which aim at tightly controlling the chunk transfer delay, and loss-based Additive Increase Multiplicative Decrease (AIMD) rate controllers, which are designed to be more aggressive and can compete with other AIMD congestion controls, i.e., TCP.Both families of mechanisms are implemented in a full-fledged P2P-TV application that we use to collect performance results. Only actual experiments – conducted both in a controlled test-bed and over the wild Internet, and involving up to 1800 peers – are presented to assess performance in realistic scenarios.Results show that DB-HRC tends to outperform AIMD-HRC when tight buffering time constraints are imposed to the application, while AIMD-HRC tends to be preferable in severely congested scenarios, especially when the buffering time constraints are relaxed.

Nonlinear AIMD Congestion Control and Contraction Mappings

This papers analyzes a class of nonlinear additive-increase multiplicative-decrease (AIMD) protocols that are widely deployed in communication networks. It is demonstrated that the use of these protocols guarantees that the system has a unique stable outcome to which it converges geometrically under all starting points. The development is based on a contraction argument and the derivation of explicit bounds on the contraction coefficient of corresponding operators in terms of the network parameters. In particular, bounds on the corresponding rate of convergence are obtained, improving upon known bounds for standard (linear) AIMD networks.

Adaptive AIMD Congestion Control

The main objectives of a congestion control algorithm are high bandwidth utilization, fairness and responsiveness in a changing environment. However, these objectives are contradicting in particular situations since the algorithm constantly has to probe available bandwidth, which may affect its stability. This paper proposes a novel congestion control algorithm that achieves high bandwidth utilization providing fairness among competing connections and, on the other hand, is sufficiently responsive to changes of available bandwidth. The main idea of the algorithm is to use adaptive setting for the additive increase/multiplicative decrease (AIMD) congestion control scheme, where parameters may change dynamically, with respect to the current network conditions.

TCP in wireless environments: problems and solutions

The Internet provides a platform for rapid and timely information exchange among a disparate array of clients and servers. TCP and IP are separately designed and closely tied protocols that define the rules of communication between end hosts, and are the most commonly used protocol suite for data transfer in the Internet. The combination of TCP/IP dominates today's communication in various networks from the wired backbone to the heterogeneous network due to its remarkable simplicity and reliability, TCP has become the de facto standard used in most applications ranging from interactive sessions such as Telnet and HTTP, to bulk data transfer like FTP. TCP was originally designed primarily for wired networks. In a wired network, random bit error rate, a characteristic usually more pronounced in the wireless network, is negligible, and congestion is the main cause of packet loss. The emerging wireless applications, especially high-speed multimedia services and the advent of wireless IP communications carried by the Internet, call for calibration and sophisticated enhancement or modifications of this protocol suite for improved performance. Based on the assumption that packet losses are signals of network congestion, the additive increase multiplicative decrease congestion control of the standard TCP protocol reaches the steady state, which reflects the protocol's efficiency in terms of throughput and link utilization. However, this assumption does not hold when the end-to-end path also includes wireless links. Factors such as high BER, unstable channel characteristics, and user mobility may all contribute to packet losses. Many studies have shown that the unmodified standard TCP performs poorly in a wireless environment due to its inability to distinguish packet losses caused by network congestion from those attributed to transmission errors. In this article, following a brief introduction to TCP, we analyze the problems TCP exhibits in the wireless IP communication environment, and illustrate viable solutions by detailed examples.

Analysis and design of AIMD congestion control algorithms in communication networks

We present a model of a network of synchronised sources operating additive increase multiplicative decrease (AIMD) congestion control algorithms. We show: (i) that networks of such devices in the presence of a drop-tail bottleneck buffer may be modelled as a positive linear system; (ii) that such networks possess a unique stationary point; and (iii) that this stationary point is globally exponentially stable. We use these results to establish conditions for the fair co-existence of traffic in networks employing heterogeneous AIMD algorithms and to design a new protocol for operation over high-speed and long-distance links.

On the throughput analysis of rate-based and window-based congestion control schemes

The existing TCP protocols contribute to the stability of the Internet by deploying window-based additive-increase multiplicative-decrease (AIMD) congestion control. However, the window-based congestion control is not favorable in the existence of long propagation delay and for real-time multimedia traffic. Thus, the rate-based congestion control has become an attractive alternative for the links with high delay and for multimedia flows. In this paper, an analysis of the rate-based generic AIMD congestion control scheme is presented. The analytical model is validated via simulation experiments for a wide range of link conditions and the effects of rate-increase and decrease parameters on the performance are investigated. One important result of this analysis is that throughput performance of the rate-based schemes is inversely proportional to square-root of the propagation delay whereas that of the window-based schemes is known to be inversely proportional to the propagation delay itself. This result also justifies that the rate-based congestion control schemes have higher resilience to the high link delay than the window-based schemes.