Initial Congestion Window Research Articles

Adaptive Online Decision Method for Initial Congestion Window in 5G Mobile Edge Computing Using Deep Reinforcement Learning

Mobile edge computing provides users with low response time and avoids unnecessary data transmission. Due to the deployment of 5G, the emerging edge systems can provide gigabit bandwidth. However, network protocols have not evolved together. In TCP, the initial congestion window (IW) is such a low value that most short flows still stay in slow start phase when finishing, and do not fully utilize available bandwidth. Naively increasing IW may result in congestion, which causes long latency. Moreover, since the network environment is dynamic, we have a challenging problem—how to adaptively adjust IW such that flow completion time is optimized, while congestion is minimized. In this paper, we propose an adaptive online decision method to solve the problem, which learns the best policy using deep reinforcement learning stably and fast. In addition, we propose an approach to further improve the performance by supervised learning, using data collected during online learning. We also propose to adopt SDN to address the challenges in implementing our method in MEC systems. To evaluate our method, we build an MEC simulator based on ns3. Our simulations demonstrate that our method performs better than existing methods. It can effectively reduce FCT with little congestion caused.

Access Latency Reduction in the QUIC Protocol Based on Communication History

Internet traffic is experiencing rapid growth, with the majority of traffic generated from video steaming, web data services and Internet of Things. As these services include the transmission of small data, such as web pages, video chunks and sensing data, data latency affects the quality of experience rather than the throughput. Therefore, this study aims to decrease latency to improve the quality of the user experience. To this end, we measure the web service delay and throughput in mobile networks. The results indicate a low quality experience for mobile users, even though mobile networks support a large throughput. We therefore propose a light-weight latency reduction scheme for the Quick UDP Internet Connections (QUIC) protocol. The proposed scheme calculates the average congestion window, which is utilized as the initial congestion window when a new connection is established. The proposed scheme is evaluated through experiments on a testbed. The results show that our scheme reduces latency significantly. The results of this study can help improve user experiences of video streaming and web data services.

TCP’s Initial Window—Deployment in the Wild and Its Impact on Performance

TCP congestion control and particularly its initial congestion window (IW) size is one long-debated topic that can influence Web performance. Its size is, however, assumed to be static by IETF recommendations—despite being network- and application-dependent—and only infrequently changed in its history. To understand if the standardization and research perspective still meets Internet reality, we study the IW configurations in IPv4 and of major content delivery networks (CDNs). We have been regularly inspecting IPv4 for HTTP and TLS servers to investigate their IW configuration and found a steady increase in IETF-recommended configurations. We additionally study how CDNs configure their IWs given their relevance for content distribution. To shed light on network-dependent CDN configurations, we use a globally distributed infrastructure of VPNs giving access to residential access links. We observe that most CDNs are well aware of the IW’s impact and find a high amount of customization that is beyond current Internet standards. We find various initial window configurations, most below 50 segments, yet, with exceptions of up to 100 segments—the tenfold of current standards. This paper highlights that Internet reality has drifted away from recommended and standardized practices. Driven by these findings, we investigate the effects of this new reality on the slow start of Cubic and BBR congestion controlled TCP flows. We find that TCP pacing is a key to enable increased IWs when competing against other traffic.

Comparison of end-to-end and network-supported fast startup congestion control schemes

A fundamental challenge for congestion control is the flow startup phase after the connection setup or after long idle periods. The Transmission Control Protocol (TCP) uses the time-consuming Slow-Start mechanism in that case. The objective of fast startup congestion control is to fully utilize a path much more rapidly. Faster startups can either be realized by new end-to-end congestion control mechanisms that change the Slow-Start algorithm, or by additional on-path signaling providing information about the path. This paper comprehensively compares end-to-end and network-supported fast startup schemes. We evaluate both the potential performance benefit and risk, using analytical models, simulation results, and experiments with real applications. Concerning end-to-end schemes, we study both a simple increase of the initial congestion window and the recently proposed Jump-Start mechanism. The considered network-supported schemes are the Quick-Start TCP extension and the Rate Control Protocol (RCP). They can all significantly reduce the transport delay of mid-sized data transfers, in particular over broadband networks with a non-negligible latency. As a result, fast startup schemes can significantly speed up Internet application with such traffic patterns. Our results also reveal that end-to-end approaches are not necessarily overly aggressive. Network-supported mechanisms can reduce the risk of congestion, but there are several unsolved open issues. In summary, we argue that end-to-end fast startup schemes such as an increased initial congestion window would be a promising solution for the Internet.

An argument for increasing TCP's initial congestion window

TCP flows start with an initial congestion window of at most four segments or approximately 4KB of data. Because most Web transactions are short-lived, the initial congestion window is a critical TCP parameter in determining how quickly flows can finish. While the global network access speeds increased dramatically on average in the past decade, the standard value of TCP's initial congestion window has remained unchanged. In this paper, we propose to increase TCP's initial congestion window to at least ten segments (about 15KB). Through large-scale Internet experiments, we quantify the latency benefits and costs of using a larger window, as functions of network bandwidth, round-trip time (RTT), bandwidth-delay product (BDP), and nature of applications. We show that the average latency of HTTP responses improved by approximately 10% with the largest benefits being demonstrated in high RTT and BDP networks. The latency of low bandwidth networks also improved by a significant amount in our experiments. The average retransmission rate increased by a modest 0.5%, with most of the increase coming from applications that effectively circumvent TCP's slow start algorithm by using multiple concurrent connections. Based on the results from our experiments, we believe the initial congestion window should be at least ten segments and the same be investigated for standardization by the IETF.

Adaptive Congestion Control of mSCTP for Vertical Handover Based on Bandwidth Estimation in Heterogeneous Wireless Networks

This paper proposes a new congestion control scheme of mobile Stream Control Transmission Protocol (mSCTP) for vertical handover across heterogeneous wireless/mobile networks. The proposed scheme is based on the estimation of available bandwidths in the underlying network as a cross-layer optimization approach. For congestion control of mSCTP, the initial congestion window size of the new primary path is adaptively configured, depending on the available bandwidth of the new link that a mobile node moves into. By ns-2 simulation, the proposed scheme is compared with the existing congestion control schemes in the throughput perspective. From the numerical results, we can see that the proposed mSCTP congestion control scheme could give better performance than the existing schemes in the wireless networks with an amount of background traffic.

TCP performance in wireless networks with delay spike and different initial congestion window sizes

Previous research indicates that increasing the initial congestion window size in transmission control protocol (TCP) from one segment to roughly 4 KB can significantly improve its performance for file transfers that are small compared to the link bandwidth-delay product in wireless cellular networks. However, these networks are also likely to experience delay spikes exceeding the typical round-trip-time (RTT) figures, which can cause spurious timeouts that lead to unnecessary retransmissions and reduction of the TCP sender's transmission rate. Consequently, additional unnecessary retransmissions are needed for a large initial congestion window and thus the throughput of the TCP is degraded. This paper presents the research results on using large initial windows over wireless cellular networks. It has been shown that the throughput of TCP connection over a single bottleneck link with first-in-first-out (FIFO) transmission is degraded with enlarging initial window in the presence of delay spikes. Furthermore, TCP throughput performance is kept unchanged in the simple network topology when there is no burst delay. All these findings should be considered while setting up initial congestion window.

Performance analysis of the TCP behavior in a geo satellite environment

The paper shows the main problems that the Transmission Control Protocol (TCP) meets in a Geo Stationary Orbit (GEO) satellite environment characterized by high ‘delay per bandwidth product’. In a GEO environment, the delay in the delivery of a message is very high, the Round Trip Time (RTT) is above 500 ms. These characteristics heavily affect the acknowledgement mechanism on which the TCP is based and the performance of the protocol is much lower than in cable networks. The paper proposes and analyses possible solutions aimed at mitigating the negative effect and at improving the performance. A real test-bed is used to carry out the study: two remote hosts are connected together through a satellite link in the Ka-band (20–30 GHz) by using IP routers. The system has been tested by using a ftp-like application, that allows transferring data of variable size between the two hosts. This is due to the observation that most of the Internet multimedia applications, as browsing and distance learning, use massive file transfer. The protocol behavior is investigated both by tuning the parameters buffer size and initial congestion window and by modifying the dynamic characteristics of the slow start algorithm. The analysis itself allows suggesting solutions and taking decisions.

TCP modifications over satellite channels: study and performance evaluation

AbstractThe paper presents a study and an analysis of the performance offered by TCP over a GEO (geostationary orbit) satellite link. The characteristics of satellite channels (notably the large round trip delay) heavily influence the TCP flow control, which is essentially based on acknowledgements. The effect is a delay in the acknowledgement reception and, consequently, in the delivery of messages, with respect to cabled networks. The drawbacks of using TCP in a satellite environment may be mitigated by a proper tuning of some TCP parameters. The behaviour of the protocol, as a consequence of variations in the buffer length of both transmitter and receiver and in the initial congestion window, is investigated in the paper and a proper configuration that drastically improves performance (measured by the throughput in bytes/s and by the overall transmission time) is proposed. Two test environments have been used to evaluate the proposed modifications: a real testbed, composed of two remote hosts connected through a satellite channel, and a satellite network emulator, composed of three PCs (two of them representing two hosts, the third one reproducing the behaviour of the satellite link). In both environments, a ftp‐like application designed for the aim has represented the reference application; three different file sizes have been used and the different effect of the tuning, depending on the transfer length, has been evidenced; the analysis includes both the single application case and the multiple application case, where several connections a time share the satellite link. Copyright © 2001 John Wiley & Sons, Ltd.

A web server's view of the transport layer

This paper presents observations of traffic to and from a particular World-Wide Web server over the course a year and a half. This paper presents a longitudinal look at various network path properties, as well as the implementation status of various protocol options and mechanisms. In particular, this paper considers how World-Wide Web clients utilize TCP connections to transfer web data; the deployment of various TCP and HTTP options; the range of round-trip times observed in the network; packet sizes used for WWW transfers; the implications of the measured advertised window sizes; and the impact of using larger initial congestion window sizes. These properties/mechanisms and their implications are explored. An additional goal of this paper is to provide information to help researchers better simulate and emulate realistic networks.