Explicit Control Protocol Research Articles

Stability Analysis of XCP (eXplicit Control Protocol) with Heterogeneous Flows

In this paper, we analyze the stability of XCP (eXplicit Control Protocol) in a network with heterogeneous XCP flows (i.e., XCP flows with different propagation delays). Specifically, we model a network with heterogeneous XCP flows using fluid-flow approximation. We then derive the conditions that XCP control parameters should satisfy for stable XCP operation. Furthermore, through several numerical examples and simulation results, we quantitatively investigate effect of system parameters and XCP control parameters on stability of the XCP protocol. Our findings include: (1) when XCP flows are heterogeneous, XCP operates more stably than the case when XCP flows are homogeneous, (2) conversely, when variation in propagation delays of XCP flows is large, operation of XCP becomes unstable, and (3) the output link bandwidth of an XCP router is independent of stability of the XCP protocol.

Towards experimental evaluation of explicit congestion control

Innovative efforts to provide a clean-slate design of congestion control for future high-speed heterogeneous networks have recently led to the development of explicit congestion control. These methods rely on multi-byte router feedback and aim to contribute to the design of a more scalable Internet of tomorrow. However, experimental evaluation and deployment experience with these approaches is still limited to either low bandwidth networks or simple topologies. In addition, all existing implementations are exclusively applicable to either rate- or window-based protocols and are unable to study performance of different protocols on a common platform. This paper aims to fill this void by designing a unified Linux implementation framework for both rate- and window-based methods that does not incur any interference with the system's network stack or applications. Using this implementation, we implement and reveal several key properties of four recent explicit congestion control protocols XCP, JetMax, RCP, and PIQI-RCP using Emulab's gigabit testbed with a ariety of simple yet representative network topologies. Our experiments not only confirm the known behavior of these methods, but also demonstrate their previously undocumented properties (e.g., RCP's transient overshoot under abrupt traffic load changes and JetMax's low utilization in the presence mice flows).

An efficient and fair explicit congestion control protocol for high bandwidth-delay product networks

XCP and VCP can achieve excellent performance under high bandwidth-delay product networks, but they all have some defects. In XCP, router needs to calculate a feedback for each departing packet, the cost will be un-negligible in high-speed networks. In VCP, router classifies the degree of congestion into three regions and encodes it in ECN bits to guide sender to update its congestion window ( cwnd). Obviously, the feedback in VCP is still not precise enough so that VCP has slow fairness convergence speed. Moreover VCP does not consider the TCP unfairness problem induced by heterogeneous packet sizes. Furthermore, both XCP and VCP cannot solve unfairness problem led by multiple bottleneck routers. To overcome drawbacks in XCP and VCP, we propose a new efficient and fair explicit congestion control protocol in this paper, for convenience, we call it EFXCP. In a sample interval, EFXCP router calculates an expected fair throughput and feedbacks it to senders. EFXCP sender updates its cwnd to make its’ throughput converge to expected fair throughput so that the system can rapidly converge to the optimal state. On the one hand, EFXCP calculates feedback only once in a sample interval, the calculation cost is much less than that in XCP. On the other hand, EFXCP adopts the precise feedback, the fairness convergence speed is much faster than that in VCP. Furthermore, one outstanding advantage of EFXCP is that it can achieve excellent fairness in all cases, all competing flows have almost the same throughput when system is stable. Using control theory, we demonstrate that EFXCP is global asymptotic stable regardless of bottleneck capacity, round trip delay time (RTT) and number of sources. Moreover, we quantificationally analyze the rise time and the fairness convergence time of EFXCP. Further, we evaluate the performance of EFXCP using extensive NS2 simulations over a wide range of network scenarios, the results show that EFXCP retains the advantages of XCP and VCP, and discards their disadvantages, and achieves excellent performance. Moreover, like VCP and XCP, the router does not maintain per-flow state.

Dynamic characteristics of explicit control protocol

The dynamic characteristics of eplicit control protocol (XCP) were investigated with single bottleneck on the microscopic time-scale. Analysis and simulation results show that the bandwidth utilization of an XCP bottleneck link converges to 1 at exponential rate, persistent congestion cannot occur at the bottleneck link, and throughput of an arbitrary subset of XCP flows at the bottleneck link converges to its fair share in exponential rate. The XCP has high bandwidth utilization and good fairness properties.

Stability Analysis of Explicit Congestion Control Protocols

In the context of explicit congestion control protocols like XCP and RCP where the equilibrium queue lengths are zero, we show that the stability region derived from traditional Nyquist analysis is not an accurate representation of the actual stability region, and that the use of switched linear system models with time delay and new Lyapunov tools can provide sound sufficient stability conditions.

Rate-based pacing for small buffered optical packet-switched networks

Feature Issue on Transmission in Optically Transparent Core NetworksOne of the difficulties of optical packet-switched (OPS) networks is buffering optical packets in the network. O(1) reading operation is not possible in the optical domain, because there is no equivalent optical RAM available for storing packets. Currently, the only available solution that can be used for buffering in the optical domain is using long fiber lines called fiber delay lines (FDL). However, FDLs have important limitations and may cause high packet drop rates due to the burstiness of Internet traffic. We propose an architecture using an explicit congestion control protocol (XCP) based utilization control algorithm designed for OPS wavelength-division-multiplexing (WDM) networks with pacing at the edge nodes for decreasing the buffer requirements at core nodes. We evaluate the FDL requirements on a meshed network with multiple-hop paths and show how FDL requirements change with slot size, utilization, FDL granularity, scheduling, and packet size distribution.

A Max-Min Fairness Congestion Control for Layered Streaming of Scalable Video

In a best-effort networking environment, efficient and fair congestion control is highly desired for every traffic flow to share the bandwidth appropriately. This paper proposes a congestion control algorithm for user datagram protocol rate-based layered streaming of scalable video, e.g., 3-D wavelet based scalable video streaming, which provides a variety of video bit rates. This proposed congestion control mechanism, as an extension of explicit control protocol that is a newly proposed congestion control protocol believed to be superior to transport control protocol, accommodates both window-based and rate-based flows to the heterogeneous network environment which can include wired and wireless channels. This paper further introduces the notion of reserved packet length so that the traffic of layered video can better share the bandwidth of a network by taking account of the max-min fairness with other traffic

XCP for shared-access multi-rate media

The eXplicit Control Protocol (XCP) was developed to overcome some of the limitations of TCP, such as low utilization in high bandwidth delay product networks, unstable throughput, large queue build-up, and limited fairness. XCP, however, requires that each queue controller in a path knows the exact capacity of its link. In shared access media, e.g. IEEE 802.11, knowing the actual capacity of the channel is a difficult task.In this paper we propose modifications to the XCP algorithm that enable the utilization of XCP even when the capacity of a link is unknown. These modifications are validated through simulation.We also present the results of a comparison between the performance of the modified XCP and TCP, where XCP controlled flows result more stable, fairness increases, and the network delay becomes lower. In addition, as the bandwidth delay product increases, XCP is able to maintain near-maximum utilization while TCP decreases utilization.

Transport protocols for high performance

The Explicit Control Protocol and other new congestion-control systems greatly improve application performance over a range of network infrastructure, including extremely high-speed and high-delay links. What then is next for TCP and other established but less-capable Internet protocols?

Congestion control for high bandwidth-delay product networks

Theory and experiments show that as the per-flow product of bandwidth and latency increases, TCP becomes inefficient and prone to instability, regardless of the queuing scheme. This failing becomes increasingly important as the Internet evolves to incorporate very high-bandwidth optical links and more large-delay satellite links.To address this problem, we develop a novel approach to Internet congestion control that outperforms TCP in conventional environments, and remains efficient, fair, scalable, and stable as the bandwidth-delay product increases. This new eXplicit Control Protocol, XCP, generalizes the Explicit Congestion Notification proposal (ECN). In addition, XCP introduces the new concept of decoupling utilization control from fairness control. This allows a more flexible and analytically tractable protocol design and opens new avenues for service differentiation.Using a control theory framework, we model XCP and demonstrate it is stable and efficient regardless of the link capacity, the round trip delay, and the number of sources. Extensive packet-level simulations show that XCP outperforms TCP in both conventional and high bandwidth-delay environments. Further, XCP achieves fair bandwidth allocation, high utilization, small standing queue size, and near-zero packet drops, with both steady and highly varying traffic. Additionally, the new protocol does not maintain any per-flow state in routers and requires few CPU cycles per packet, which makes it implementable in high-speed routers.