A Compound TCP Approach for High-Speed and Long Distance Networks

Abstract

Many applications require fast data transfer over high speed and long distance networks. However, standard TCP fails to fully utilize the network capacity due to the limitation in its conservative congestion control (CC) algorithm. Some works have been proposed to improve the connection's throughput by adopting more aggressive loss-based CC algorithms. These algorithms, although can effectively improve the link utilization, have the weakness of poor RTT fairness. Further, they may severely decrease the performance of regular TCP flows that traverse the same network path. On the other hand, pure delay-based approaches that improve the throughput in high-speed networks may not work well when the traffic is mixed with both delaybased and greedy loss-based flows. In this paper, we propose a novel Compound TCP (CTCP) approach, which is a synergy of delay-based and loss-based approach. Specifically, we add a scalable delay-based component into the standard TCP Reno congestion avoidance algorithm (a.k.a., the loss-based component). The sending rate of CTCP is controlled by both components. This new delay-based component can rapidly increase sending rate when network path is under utilized, but gracefully retreat in a busy network when bottleneck queue is built. Augmented with this delay-based component, CTCP provides very good bandwidth scalability with improved RTT fairness, and at the same time achieves good TCP-fairness, irrelevant to the windows size. We developed an analytical model of CTCP and implemented it on the Windows operating system. Our analysis and experiment results verify the properties of CTCP.Index Terms-TCP performance, delay-based congestion control, high speed network I. INTRODUCTION Moving bulk data quickly over high-speed data network is a requirement for many applications. For example, the physicists at CERN LHC conduct physics experiments that generate gigabytes of data per second, which are required to be shared among other scientists around the world [2]. Currently, most applications use the Transmission Control Protocol (TCP) to transmit data over the Internet. TCP provides reliable data transmission with embedded congestion control algorithm [1] which effectively removes congestion collapses in the Internet by adjusting the sending rate according to the available bandwidth of the network. However, although TCP achieves remarkable success (maximizing the utilization of the link and fairly sharing bandwidth between competing flows) in today's Internet environment, it has been reported that TCP substantially underutilizes network bandwidth over high-speed and long distance networks [4].In high-speed and long distance networks, TCP requires a

Oscillations of the Sending Window in Compound TCP

“…Figure 4 in [5], and some of the comments in that paper, give the impression that the window is then kept constant for a certain time.…”

“…While this might be a useful approximation in explaining and thinking about this new TCP version, it is easy to see, from equation (5) in [5], that the window will indeed oscillate during this phase. Figure 1 shows the evolution of the sending window from an ns-2 simulation.…”

“…Tan et al have introduced Compound TCP [5] to improve the performance of TCP on networks with large bandwidth delay products. One of the main ideas of this new high speed TCP variant is to quickly increase the sending window as long as the network is underutilized and then stabilizing it when a certain number of packets is bu ered in the network.…”

NF-TCP: A Network Friendly TCP Variant for Background Delay-Insensitive Applications

“…Efficiently utilizing available bandwidth is another consideration driving existing solutions for high BDP environments, such as High-speed TCP [8], FAST [9], Compound TCP [10], CUBIC [11], Quick-Start [12] and XCP [13]. However, part of their ability to opportunistically utilize the large bandwidths in these types of environments is due to their aggressive increase policies.…”

Making a Case for Proactive Flow Control in Optical Circuit-Switched Networks

“…In order to improve TCP performance, significant research has been done to improve TCP congestion control [16,13,10,9]. Other complementary research has been done to improve flow control [11,14,5].…”