LIAD: Adaptive bandwidth prediction based Logarithmic Increase Adaptive Decrease for TCP congestion control in heterogeneous wireless networks

For accessing plentiful resources in the Internet through wireless mobile hosts, diverse wireless network standards and technologies have been developed and progressed significantly. The most successful examples include IEEE 802.11 WiFi for wireless networks and 3G/HSDPA/HSUPA for cellular communications. All IP-based applications are the primary motivations to make these networks successful. In TCP/IP transmissions, the TCP congestion control operates well in the wired network, but it is difficult to determine an accurate congestion window in a heterogeneous wireless network that consists of the wired Internet and various types of wireless networks. The primary reason is that TCP connections are impacted by not only networks congestion but also error wireless links. This paper thus proposes a novel adaptive window congestion control (namely Logarithmic Increase Adaptive Decrease, LIAD) for TCP connections in heterogeneous wireless networks. The proposed RTT-based LIAD has the capability to increase throughput while achieving competitive fairness among connections with the same TCP congestion mechanism and supporting friendliness among connections with different TCP congestion control mechanisms. In the Congestion Avoidance (CA) phase, an optimal shrink factor is first proposed for Adaptive Decreasing cwnd rather than a static decreasing mechanism used by most approaches. Second, we adopt a Logarithmic Increase algorithm to increase cwnd while receiving each ACK after causing three duplicate ACKs. The analyses of congestion window and throughput under different packet loss rate are analyzed. Furthermore, the state transition diagram of LIAD is detailed. Numerical results demonstrate that the proposed LIAD outperforms other approaches in goodput, fairness, and friendliness under diverse heterogeneous wireless topologies. Especially, in the case of 10% packet loss rate in wireless links, the proposed approach increases goodput up to 156% and 1136% as compared with LogWestwood+ and NewReno, respectively.     

TCP in a wireless world

Mobile wireless is one of the more challenging environments for the Internet protocols, and for TCP in particular. One approach to supporting the wireless environment is the so-called “walled garden”. Here the transport protocol used within the mobile wireless environment is not TCP, but is instead a transport protocol that has been specifically adapted to mobile wireless. In this model, Internet applications interact with an application gateway to reach the wireless world, and the application gateway uses a wireless transport protocol and potentially a modified version of the application data to interact with the wireless device. The most common implementation of this approach is to extend a Web client into the mobile wireless device, using some form of proxy server at the boundary of the wireless network and the Internet. This is the approach adopted by the Wireless Access Protocol (WAP) Forum. An alternative is to allow mobile wireless devices to function as any other Internet-connected device. This approach requires some form of end-to-end direct IP continuity and an associated end-to-end TCP functionality, where the TCP path straddles both wired and wireless segments. Ensuring the efficient operation of TCP in this environment becomes integral to the development of the environment itself; the problem is no longer one of adjusting TCP to match the requirements of the wireless environment, but one of providing seamless interworking between the wired and wireless worlds     

Using traffic asymmetry to enhance TCP performance

A wealth of recent work has gone into optimizing the performance of Transmission Control Protocol (TCP) on the downlink channel of wireless networks such as for example, honing its congestion awareness mechanism so that it is minimally affected by random wireless losses, and optimizing achieved fairness of the end-to-end TCP rates. Other work has gone into balancing the allocation of a shared resource between the downlink and uplink in order to optimize TCP performance. We build on such previous research by proposing a cross-layer algorithm for resource allocation in OFDMA systems aiming not only to achieve optimal throughput for competing TCP flows but also to allocate resources appropriately between the downlink and uplink. This is important due to the increasing number of Internet applications where the mobile terminal is the TCP sender (social networking, peer-to-peer, etc.). Therefore, our scheme makes use of the asymmetry in the traffic and by defining the boundary between downlink and uplink capacity dynamically, enhance the TCP performance. Through numerical investigations we show the performance of the proposed scheme in terms of achieved fairness to the receivers and efficient allocation of downlink to uplink ratios based on the TCP traffic.     

Evaluating transport protocol performance over a wireless mesh backbone

IEEE 802.11n wireless physical layer technology increases the deployment of high throughput wireless indoor mesh backbones for ubiquitous Internet connectivity at the urban and metropolitan areas. Most of the network traffic flows in today’s Internet use ‘Transmission Control Protocol’ (TCP) as the transport layer protocol. There has been extensive works that deal with TCP issues over wireless mesh networks as well as noisy wireless channels. Further, IEEE 802.11n is well known for its susceptibility to increased channel losses during high data rate communication. This paper investigates the dynamics of an end-to-end transport layer protocol like TCP in the presence of burst and correlated losses during IEEE 802.11n high data rate communication, while maintaining fairness among all the end-to-end flows. For this purpose, we evaluate four TCP variants-Loss Tolerant TCP (LT-TCP), Network Coded TCP (TCP/NC), TCP-Horizon and Wireless Control Protocol (WCP), where the first two protocols are known to perform very well in extreme lossy networks, and the last two are specifically designed for mesh networks. Our evaluation shows that WCP performs better in a IEEE 802.11n supported mesh networks compared to other three variants. However, WCP also results in negative impact at high data rates, where end-to-end goodput drops with the increase in physical data rate. The analysis of the results reveals that explicit loss notifications and flow balancing are not sufficient to improve transport protocol performance in an IEEE 802.11n supported mesh backbone, rather a specific mechanism is required to synchronize the transport queue management with lower layer scheduling that depends on IEEE 802.11n features, like channel bonding and frame aggregation. The findings of this paper give the direction to design a new transport protocol that can utilize the full capacity of IEEE 802.11n mesh backbone.     

Can the current generation of wireless mesh networks compete with cellular voice?

Wireless mesh networks are being deployed to provide broadband wireless connectivity to city-wide hotspots. The typical architecture in these deployments thus far is a single-radio architecture: mesh nodes carry only one radio, which is used both to receive the traffic from the clients and to relay this traffic through the mesh to the wired Internet gateway.In this paper, we study the performance of a representative single-radio mesh network both in a live setup and in a laboratory environment. We characterize the performance of different applications (e.g. VoIP), and study some key challenges of mesh networks such as the fairness in bandwidth allocation and hidden node terminal. Finally, we compare the results of the study with traditional cellular networks, and discuss various options to enhance the performance of wireless mesh networks in the future.     

A Lightweight Fairness-Driven AQM for Regulating Bandwidth Utilization in Best-Effort Routers

The end-to-end congestion control mechanism of transmission control protocol (TCP) is critical to the robustness and fairness of the best-effort Internet. Since it is no longer practical to rely on end-systems to cooperatively deploy congestion control mechanisms, the network itself must now participate in regulating its own resource utilization. To that end, fairness-driven active queue management (AQM) is promising in sharing the scarce bandwidth among competing flows in a fair manner. However, most of the existing fairness-driven AQM schemes cannot provide efficient and fair bandwidth allocation while being scalable. This paper presents a novel fairness-driven AQM scheme, called CHORD (CHOKe with recent drop history) that seeks to maximize fair bandwidth sharing among aggregate flows while retaining the scalability in terms of the minimum possible state space and per-packet processing costs. Fairness is enforced by identifying and restricting high-bandwidth unresponsive flows at the time of congestion with a lightweight control function. The identification mechanism consists of a fixed-size cache to capture the history of recent drops with a state space equal to the size of the cache. The restriction mechanism is stateless with two matching trial phases and an adaptive drawing factor to take a strong punitive measure against the identified high-bandwidth unresponsive flows in proportion to the average buffer occupancy. Comprehensive performance evaluation indicates that among other well-known AQM schemes of comparable complexities, CHORD provides enhanced TCP goodput and intra-protocol fairness and is well-suited for fair bandwidth allocation to aggregate traffic across a wide range of packet and buffer sizes at a bottleneck router.     

Investigating the performance of TCP in mobile ad hoc networks

Mobile ad hoc networks have several inherent characteristics (e.g. dynamic topology, time-varying and bandwidth constrained wireless channels, multi-hop routing, and distributed control and management). The goal of this work is to investigate the impact of these characteristics on the performance of TCP. First, we investigate throughput performance of TCP as a function of path length (i.e. multiple wireless hops), node mobility, and traffic intensity. Next, we examine the ‘fairness’ of the ad hoc network with regard to equal sharing of network bandwidth among multiple TCP flows. Third, we evaluate the impact of two on-demand routing protocols (i.e. AODV and DSR) on the throughput of TCP. Finally, a factorial design experiment is conducted to quantify the effects and interactions of three factors, which influence the throughput of TCP. These factors include routing, node speed, and node pause time. Two key results were observed. Results show that traffic intensity (e.g. number of concurrent flows) is significantly affects TCP throughput, suggesting the need for congestion control, scheduling and traffic management schemes. Second, source routing achieves higher throughputs while also generating significantly less routing overhead than AODV. Results also show that in some instances, the fairness of the network is very uneven among concurrent TCP flows, resulting in several sending stations achieving very little or no throughput.     

Efficiency/Fairness Tradeoffs in Networks with Wireless Components and Transient Congestion

Our work explores the impact of aggressive/conservative congestion control strategies on the fairness and efficiency of reliable transport protocols, in a wired/wireless environment. Based on experiments, we study the behavior of congestion control mechanisms in response to wireless errors, and transient congestion caused by a small number of competing flows. We show that: (i) the traditional TCP algorithm proves to be inadequate in terms of efficiency and fairness when random wireless errors occur in the network and, (ii) an aggressive strategy does not necessarily yield better performance. On the contrary, in the combined presence of transmission errors and transient congestion a conservative strategy appears superior.     

Mechanisms for centralized flow rate control in 802.11-based wireless mesh networks

Cross-layer interaction between TCP and CSMA/CA-based MAC in multihop wireless networks produces suboptimal network performance, including flow rate unfairness and starvation. Rate control mechanisms can mitigate this behavior. Of particular interest are centralized mechanisms that enforce rate limits at traffic aggregation points, without modifying individual mesh routers or client devices. In this paper, we propose, design, and evaluate a framework of zero-overhead, feedback-driven centralized rate controllers. These controllers are implemented at gateway mesh routers. We use existing data traffic as capacity probes with a feedback-driven response to adapt to changes in network and traffic conditions. Using simulations and experiments on a testbed, we show an improvement in fairness by a factor of 2–3 over networks without any rate control. Further, our fairness metrics are within 2% of those achieved by a centralized controller with an omniscient knowledge of network conditions.     

TCP Yuelu:一种基于有线/无线混合网络端到端的拥塞控制机制

无线链路传输数据的比特率出错导致TCP协议在有线／无线混合网络环境下性能低下,在改进算法TCPReno的基础上,文章提出了一种适用于有线／无线混合网络的拥塞控制机制,该机制包括一种分阶段平滑慢启动机制,改善了突发流量对网络性能的损害,引入网络测量技术获得了往返时间（RTT）、网络带宽、瓶颈链路队列长度等网络状态参数,区分网络拥塞和无线链路比特差错,避免了终端节点对网络状态不了解产生的盲目行为,有效改进了TCP的加性增加乘性减少（AIMD）窗口调节机制,提高了网络性能．同时,在仿真软件NS2中实现了该算法,进行了大量的仿真实验,实验结果表明TCP Yuelu有效降低了网络抖动,提高了网络传输性能,并保持了良好的公平性和对其它TCP流的友好性．     

一种改进的TCP拥塞控制算法

目前,TCP拥塞控制算法作为一种可靠的数据传输被广泛应用在因特网中．在保证网络数据传输可靠性的基础上,数据流之间的公平性是算法设计的重要的性能指标之一．在单瓶颈网络环境下对TCP数据流之间的研究算法已经被提出,但对多瓶颈网络环境下TCP数据流之间的公平性研究至今不多见．因此,根据网络层的显示拥塞指示Marking Relay ECN（explicit congestion notification,ECN）技术,研究了在多瓶颈网络环境下TCP数据流的公平性,提出了一种改进的TCP拥塞控制算法,并使该算法在IP网络中得以实现．仿真结果证明,此算法在多瓶颈网络环境下能使TCP流达到较好的数据流之间的公平性;而且所提出的算法与传统的TCP算法相比,有更高的吞吐量和更快的响应．总之,所提算法性能表现良好．     

Behavior analysis of TCP Linux variants

The Transmission Control Protocol (TCP) is used by the vast majority of Internet applications. Since its introduction in the 1970s, a lot of variants have been proposed to cope with the different network conditions we can have (e.g., wired networks, wireless networks, satellite links) and nowadays Linux OS includes 13 different TCP variants.The aim of this paper is to offer a comparative analysis of the behavior of the different TCP Linux variants, in terms of throughput, fairness, and friendliness.     

Achieving high throughput and TCP Reno fairness in delay-based TCP over large networks

The transport control protocol (TCP) has been widely used in wired and wireless Internet applications such as FTP, email and http. Numerous congestion avoidance algorithms have been proposed to improve the performance of TCP in various scenarios, especially for high speed and wireless networks. Although different algorithms may achieve different performance improvements under different network conditions, designing a congestion algorithm that can perform well across a wide spectrum of network conditions remains a great challenge. Delay-based TCP has a potential to overcome above challenges. However, the unfairness problem of delay-based TCP with TCP Reno blocks widely the deployment of delay-based TCP over wide area networks. In this paper, we proposed a novel delay-based congestion control algorithm, named FAST-FIT, which could perform gracefully in both ultra high speed networks and wide area networks, as well as keep graceful fairness with widely deployed TCP Reno hosts. FAST-FIT uses queuing delay as a primary input for controlling TCP congestion window. Packet loss is used as a secondary signal to adaptively adjust parameters of primary control process. Theoretical analysis and experimental results show that the performance of the algorithm is significantly improved as compared to other state-of-the-art algorithms, while maintaining good fairness.     

无线Internet的业务质量及其改进

在移动网络中,移动用户对Internet的访问,具有与通常的外部Internet网络不同的特点。移动用户发出的对信息内容的请求(例如询问前方交通情况和路线),以及无线Internet信息提供商主动向移动用户发出的信息(例如移动用户附近的商品信息广告),与移动用户的位置、移动状态(方向、速度)和个人情况(userprofile)等有关。因此,要建立恰当的无线Internet流量模型和实现QoS(业务质量)控制,需要考虑用户的移动特性和在不同移动状态下访问Internet的概率分布。该文将建立一个新的定量分析模型,用半马尔可夫过程和一般的状态空间来描述移动用户的行为;并基于该移动模型,建立相应的移动用户对信息内容的访问模型、描述移动用户请求的到达过程;进而得到无线Internet业务质量参数的估计,即无线Internet对移动用户请求的平均响应时间、对无线侧和有线侧传输带宽的需求等;利用这些结果,可以实现无线资源的动态分配和允入控制。该文还将分析无线代理网关的性能、缓存容量需求,并给出改善平均响应时间的可行方案。最后用计算机模拟对提出的理论分析进行验证。     

Logarithmic window increase for TCP Westwood+ for improvement in high speed,long distance networks

The majority of current Internet applications uses Transmission Control Protocol (TCP) for ensuring reliable end-to-end delivery of data over IP networks. The resulting path is, generally speaking, characterized by fairly large propagation delays (of the order of tens to hundreds of milliseconds) and increasing available bandwidth. Current TCP¹performance is far from representing an optimal solution in such operating conditions. The main reason lies in the conservative congestion control strategy employed, which does not let TCP to exploit the always increasing available path capacity. As a consequence, TCP optimization has been an active research topic in the research community over the last 25 years, boosted in the last few years by the widespread adoption of high-speed optical fiber links in the backbone and the emergence of supercomputing networked applications from one side and tremendous growth of wireless bandwidth in network access from another. This has led to the introduction of several alternative proposals for performing congestion control. Most of them focus on the effectiveness of bandwidth utilization, introducing more “aggressive” congestion control strategies. However, such approaches result often in unfairness among flows with substantially different RTTs, or do not present the inter-protocol fairness features required for incremental network deployment.In this paper, we propose TCP LogWestwood+, a TCP Westwood+ enhancement based on a logarithmic increase function, targeting adaptation to the high-speed wireless environment. The algorithm shows low sensitivity with respect to RTT value, while maintaining high network utilization in a wide range of network settings. The performance, fairness and stability properties of the proposed TCP LogWestwood+ are studied analytically, and then validated by means of an extensive set of experiments including computer simulations and wide area Internet measurements.     

Routing Internet traffic in heterogeneous mesh networks: Analysis and algorithms

In practical wireless mesh networks (WMNs), gateways are subject to hard capacity limits on the aggregate number of flows (in terms of bit rate) that they can support. Thus, if traffic is routed in the mesh network without considering those constraints, as well as the traffic distribution, some gateways or intermediate mesh routers may rapidly get overloaded, and the network resources can be unevenly utilized. To address this problem, in this paper we firstly develop a multi-class queuing network model to analyze feasible throughput allocations, as well as average end-to-end delay, in heterogeneous WMNs. Guided by our analysis, we design a Capacity-Aware Route Selection algorithm (CARS), which allocates network paths to downstream and upstream Internet flows so as to ensure a more balanced utilization of wireless network resources and gateways’ fixed connections. Through simulations in a number of different network scenarios we show that the CARS scheme significantly outperforms conventional shortest path routing, as well as an alternative routing method that distributes the traffic load on the gateway nodes to minimize its variance.     

Receiver-driven bandwidth sharing for TCP and its application to video streaming

Applications using Transmission Control Protocol (TCP), such as web-browsers, ftp, and various peer-to-peer (P2P) programs, dominate most of the Internet traffic today. In many cases, users have bandwidth-limited last mile connections to the Internet which act as network bottlenecks. Users generally run multiple concurrent networking applications that compete for the scarce bandwidth resource. Standard TCP shares bottleneck link capacity according to connection round-trip time (RTT), and consequently may result in a bandwidth partition which does not necessarily coincide with the user's desires. In this work, we present a receiver-based bandwidth sharing system (BWSS) for allocating the capacity of last-hop access links according to user preferences. Our system does not require modifications to the TCP protocol, network infrastructure or sending hosts, making it easy to deploy. By breaking fairness between flows on the access link, the BWSS can limit the throughput fluctuations of high-priority applications. We utilize the BWSS to perform efficient video streaming over TCP to receivers with bandwidth-limited last mile connections. We demonstrate the effectiveness of our proposed system through Internet experiments.     

TCP Performance and Behaviors with Local Retransmissions

TCP has been the dominant transport protocol over the global Internet, and its performance over a hybrid wireless/wireline network has attracted much attention in recent years. This paper investigates the end-to-end TCP performance, in terms of normalized throughput, effective goodput, and packet delay, over wireless lossy links with local retransmissions. The results reveal that local retransmissions can increase the normalized TCP throughput in different wireless bandwidth, delay, and error settings, at the cost of a decrease in effective goodput and an increased packet delay. The performance observation is explained by the explored TCP endpoint behaviors, including the spurious timeout and duplicated acknowledgment. Analysis shows that spurious timeouts with local retransmissions are rare due to the conservative TCP timeout algorithm. However, spurious duplicated acknowledgments have negative impact and a further improvement with the D-SACK proposal is evaluated.     

煤矿物联网统一通信平台的研究

提出了以TCP/IP协议为核心,高速工业以太网络为主干,无线局域网、无线传感网、现场总线和RS485总线为延伸,建设煤矿物联网统一通信平台的技术方案,重点阐述了煤矿物联网统一通信平台架构、关键设备、协议体系、虚拟存取及面向服务的通信平台架构的实现方法。     

Improving TCP performance over wired–wireless networks

Today there is a growing demand for Internet services over WLAN hotspots. Majority of the Internet services today are based on TCP. However, TCP is not well-suited for heterogeneous networks consisting of wired and wireless networks. Losses in wireless network, which are quite frequent, are often misinterpreted by the TCP sender as loss due to congestion, which leads to poor performance of TCP. Hence, it is important to shield the TCP sender from wireless error. In this paper, we propose an improved method for identifying cases of wireless losses and tackling the loss at the local link level through MAC layer retransmissions. We then evaluate the effect of MAC layer retransmissions on the performance of TCP both analytically and empirically. Our empirical results show that significant improvement in TCP performance is possible through MAC layer retransmission.