Retransmission Timeout Estimation Research Articles

Geometric Series based effective RTO estimation Technique for CoCoA

Constrained Application Protocol (CoAP) is a standard data transfer protocol for Internet of Things. It has an in-built support for the basic congestion control mechanism that uses fixed Retransmission Time Out (RTO) for every transmission regardless of Round Trip Time (RTT), and performs Binary Exponential Backoff (BEB) when the packets get dropped. CoAP Simple Congestion Control/Advanced (CoCoA) is an enhanced congestion control mechanism over CoAP that adapts RTO based on RTT. It maintains Strong and Weak RTO estimators and uses a Variable Backoff Factor (VBF) instead of BEB when the packets get dropped. CoCoA uses an Exponential Weighted Moving Average (EWMA) to estimate the RTO for the next transmission. The weight used in EWMA is determined on the basis of whether the RTT estimated for the recent transmission was a Strong RTT or Weak RTT. However, the weights used to estimate the RTO are fixed (0.5 for Strong and 0.25 for Weak). These fixed weights lead to slow adaptation of RTO and affect the performance of the IoT applications. In this paper, we highlight the impact of having fixed weights while estimating the RTO in CoCoA. In particular, we show that the RTO in CoCoA fails to adapt quickly when the network conditions are lossless because it uses a fixed value for Strong RTO estimation (0.5). We propose a new algorithm called Geometric Series based effective RTO estimation Technique for CoCoA (GSRTC) to adapt the weight used in EWMA for estimating Strong RTO. GSRTC is integrated into CoCoA and validated against existing mechanisms using the Cooja simulator in Contiki OS and in a real testbed FIT/IoT-LAB. Our results show that GSRTC has lower Flow Completion Times (FCT), lesser retransmissions and better network throughput.

An Adaptive Media-Aware Retransmission Timeout Estimation Method for Low-Delay Packet Video

Time-constrained error recovery is an integral component of reliable low-delay video applications. Regardless of the error-control method adopted by the application, unacknowledged or missing packets must be quickly identified as lost or delayed, so that necessary actions can be taken by the server/client on time. Historically, this problem has been referred to as retransmission timeout (RTO) estimation. Earlier studies show that existing RTO estimators suffer from either long loss detection times or a large number of spurious timeouts. The goal of this study is to address these problems by developing an RTO estimation method specifically tailored for low-delay video applications. In the media-unaware mode, this method exploits the temporal dependence in packet delay to optimally manage the tradeoff between the amount of overwaiting and redundant retransmission rate. As opposed to existing methods, our approach is completely adaptive to the source video characteristics and time-varying network conditions, and does not use any preset parameters. In the media-aware mode, on the other hand, the timeout estimates are jointly optimized based on the importance and urgency of the video packets such that the rendering quality is maximized under the given rate constraints. With a comprehensive set of simulation and experimental results, we show that both the media-unaware and media-aware RTO estimators detect lost packets faster and more accurately than their rivals. Furthermore, our results also substantiate the fact that the media-aware RTO estimator outperforms all other RTO estimators in terms of video quality

Performance evaluation of TCP session considering long‐range dependence of RTT

AbstractRecent research has shown that long‐range dependence is found not only in network traffic volume, but also in the propagation delay time of packets. The round‐trip propagation time of packets, which is known as the round‐trip time (RTT), is one of the most important parameters for determining TCP performance. The ability to understand its characteristics can contribute to an improvement in TCP performance. Therefore, in this paper, to determine the impact of the long‐range dependence of the RTT on TCP performance, the authors looked at the two congestion control phases known as congestion avoidance and slow start in TCP window control and used computer simulations to evaluate performance. First, the evaluation related to the impact on the congestion avoidance phase showed that higher long‐range dependence and larger transfer files caused greater variability in the file transfer completion time. Next, the evaluation related to the impact on the slow start phase, which evaluated the impact of the long‐range dependence of the RTT on the TCP retransmission timeout (RTO), showed that higher long‐range dependence causes unnecessary timeouts, which end up causing the resending of packets that have not actually been lost, to occur more frequently. The authors also performed investigations for mitigating the impact of the long‐range dependence of the RTT and made a number of modifications to the existing RTO estimation algorithm to show that TCP performance can be improved. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(6): 52–60, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10073

Explicit loss indication and accurate RTO estimation for TCP error recovery using satellite links

The TCP protocol has been optimised to provide reliable operation over an internet of packet networks. A satellite link, particularly one using a terminal with a small aperture antenna, has features which differ from those of a terrestrial communication network, such as high propagation delay and a varying (often high) level of errors. Although TCP provides a reliable service, it does not always perform efficiently over a satellite link. The main weaknesses of TCP over a satellite link are the interaction between the TCP error recovery procedure and congestion control procedures and the inaccuracy of retransmission time-out estimation. These weaknesses are analysed, and a number of methods for improving the performance of TCP are presented. The improvements may be implemented by modifying the TCP transport protocol in the end-systems.