Congested Gateways Research Articles

Reliable routing for low-power smart space communications

Smart space (SS) communication has rapidly emerged as an exciting new paradigm that includes ubiquitous, grid and pervasive computing to provide intelligence, insight and vision for the emerging world of intelligent environments, products, services and human interaction. Dependable networking of a SS environment can be ensured through reliable routing, efficient selection of error-free links, rapid recovery from broken links and the avoidance of congested gateways. Since link failure and packet loss are inevitable in SS wireless sensor networks (WSNs), the authors have developed an efficient scheme to achieve a reliable data collection for SSs composed of low capacity wireless sensor nodes. WSNs must tolerate a certain lack of reliability without a significant effect on packet delivery performance, data aggregation accuracy or energy consumption. An effective hybrid scheme is presented that adaptively reduces control traffic with a metric that measures the reception success ratio of representative data packets. Based on this approach, the proposed routing scheme can achieve reduced energy consumption while ensuring minimal packet loss in environments featuring high link failure rates. The performance of the proposed routing scheme is experimentally investigated using both simulations and a test bed of TelosB motes. It is shown to be more robust and energy efficient than the network layer provided by TinyOS2.x. The results show that the scheme is able to maintain better than 95% connectivity in an interference-prone medium while achieving a 35% energy saving.

An Analysis to Improve Congestion Algorithm of TCP

Congestion is an important issue in the research of end-to-end congestion control. The congestion issue in transmission with TCP is studied. Under the situation of different round trip time and multiple congested gateways, ECC (Explicit Congestion Control) algorithm is proposed to solve the congestion problem of TCP. The basic idea is to explicitly improve Congestion by adding mechanism at both end systems and gateways. Then study the tile congestion of Internet data transmission. Internet data transmission relies on end system mechanisms to keep Congestion. As the number of the users has been very large, this scheme has become vulnerable. It is required to deploy some congestion mechanism at gateways.

Weighted fair bandwidth sharing using SCALE technique

Currently there is not enough work on the Internet weighted fair bandwidth sharing without per-flow management, especially when both UDP and TCP flows of different RTTs and different bandwidth targets coexist. This paper contains two contributions: 1. A mechanism called SCALE–WFS, Scalable Core with Aggregation Level labEling — Weighted Fair bandwidth-Sharing, is presented to achieve near-optimal Max–Min weighted fairness without per-flow management at core routers, in the context of differentiated service (Diffserv) networks. Through extensive simulation and simple analysis, we show the performance problems with current solutions and propose SCALE–WFS to solve these problems. This scheme works effectively for different flow weights, RTTs, protocols (TCP and UDP), under the scenarios of different bandwidth provisioning and multiple congested gateways, all of which we consider the basic requirements for a practical solution. 2. Apart from “per-flow” and completely “core-stateless”, SCALE represents a third management level — the label-based flow “aggregation” level. It reduces the information redundancy in the “per-flow” and surpasses the performance of the “core-stateless”. This is important to Diffserv networks where we try to avoid the non-scalability of per-flow management while keeping its good Quality of Services. In this paper, we show that SCALE–WFS is effective and scalable, robust and extensible.

The macroscopic behavior of the TCP congestion avoidance algorithm

In this paper, we analyze a performance model for the TCP Congestion Avoidance algorithm. The model predicts the bandwidth of a sustained TCP connection subjected to light to moderate packet losses, such as loss caused by network congestion. It assumes that TCP avoids retransmission timeouts and always has sufficient receiver window and sender data. The model predicts the Congestion Avoidance performance of nearly all TCP implementations under restricted conditions and of TCP with Selective Acknowledgements over a much wider range of Internet conditions.We verify the model through both simulation and live Internet measurements. The simulations test several TCP implementations under a range of loss conditions and in environments with both drop-tail and RED queuing. The model is also compared to live Internet measurements using the TReno diagnostic and real TCP implementations.We also present several applications of the model to problems of bandwidth allocation in the Internet. We use the model to analyze networks with multiple congested gateways; this analysis shows strong agreement with prior work in this area. Finally, we present several important implications about the behavior of the Internet in the presence of high load from diverse user communities.

Connections with multiple congested gateways in packet-switched networks part 1

In this paper we explore the bias in TCP/IP networks against connections with multiple congested gateways. We consider the interaction between the bias against connections with multiple congested gateways, the bias of the TCP window modification algorithm against connections with longer roundtrip times, and the bias of Drop Tail and Random Drop gateways against bursty traffic. Using simulations and a heuristic analysis, we show that in a network with the window modification algorithm in 4.3 tahoe BSD TCP and with Random Drop or Drop Tail gateways, a longer connection with multiple congested gateways can receive unacceptably low throughput. We show that in a network with no bias against connections with longer roundtrip times and with no bias against bursty traffic, a connection with multiple congested gateways can receive an acceptable level of throughput.We discuss the application of several current measures of fairness to networks with multiple congested gateways, and show that different measures of fairness have quite different implications. One view is that each connection should receive the same throughput in bytes/second, regardless of roundtrip times or numbers of congested gateways. Another view is that each connection should receive the same share of the network's scarce congested resources. In general, we believe that the fairness criteria for connections with multiple congested gateways requires further consideration.