混合网络下的TCP拥塞控制跨层优化算法

针对混合网络中并行链路间TCP流的不公平性,提出一种新的算法.此算法利用跨层设计的思想,以传输层的数据重传率为参数来调整TCP流不公平性,也就是说MAC层上的竞争窗口将根据重传率的动态变化而改变,其目的在于抑制并行链路TCP流接入信道能力的不公平性.并且用仿真工具NS2进行仿真的结果表明,采用改进算法后的网络公平性指数比未改进前提高了17.9％.该算法能明显改善并行链路间TCP流的不公平性.     

VANET/LTE-Advanced异构网络中基于协议序列-IEEE 802.11p的信道接入机制

摘要：提出了VANET/LTE-Advanced异构网络架构,并重新规划信道使用及接入模式,提高车载设备之间通信的有效性,增强公平性并兼顾自由度。以车辆间通信为研究对象,深入剖析并比较IEEE 802.11p MAC协议,基于协议序列信道接入机制,提出基于协议序列-IEEE 802.11p的信道接入算法,将“基于调度”与“基于竞争”的信道接入结合,完善IEEE 802.11p MAC层协议。仿真结果表明,基于协议序列-IEEE 802.11p的信道接入机制与UI模式及IEEE 802.11p模式相比,实现了用户平均吞吐量和平均数据分组发送时延性能的权衡,具有理论价值和实用价值。     

基于载波监听的Ad Hoc网络双信道接入协议研究

双信道接入协议在解决隐终端和暴露终端问题上具有独特的优势.基于报文监听的Ad Hoc网络双信道接入协议无法消除数据报文的冲突.本文对基于载波监听的Ad Hoc网络双信道接入协议进行了研究,提出了DCMA载波监听信道接入协议.其中DCMA_CSBI通过载波监听和BI控制报文完全解决了隐终端和暴露终端问题.文章通过仿真对DCMA协议的性能进行了分析和比较.分析结果表明DCMA_CSBI是一种非常高效实用的Ad Hoc网络双信道接入协议,载波监听对Ad Hoc网络信道接入协议而言是至关重要的.     

卫星网络中的TCP跨层技术研究

CCSDS链路层协议TC的重传功能可以减少误码丢包而导致TCP窗口缩减、吞吐量降低的情况,但是链路层对丢失的数据反复重传易引起数据包端到端传输时延的剧烈变化,可能导致TCP数据包失序和重传定时器发生超时,引起传输层和链路层重复重传的情况.该文通过链路层与传输层的差错控制信息交互,传输层将TCP数据的序列号通告链路层,链...     

认知无线电网络中一种改进的传输层协议

在认知无线电网络中,传统的TCP协议无法适应认知用户周期性感知频谱、切换信道等特点,使得网络的传输性能大大降低。在TCP-Reno基础上提出了一种基于传输预判与慢启动门限值(Slow Start Threshold,SSThresh)的自适应调整的传输层协议———TCP-Cog,该协议通过预测下一个数据包的传输时延,调整发送端的发送,并通过预测切换信道的带宽调整SSThresh。通过在NS2工具中进行仿真,验证了TCP-Cog能够提高TCP的传输速率,降低重传率,提升传输性能。     

Ad Hoc网络信道接入协议

文章首先介绍了AdHoc网络特有的隐终端和暴露终端问题 ,并对可能的解决方法进行了分析。在总结了前人工作的基础上 ,将AdHoc网络信道接入协议划分成基于单信道、双信道和多信道三类。文章还介绍了几种具有代表性的单信道接入协议 ,并给出了AdHoc网络信道接入协议的发展动向     

Ad hoc网络技术讲座第1讲 Ad hoc网络的体系结构和信道接入协议

本文首先介绍Adhoc网络的概貌,然后分析Adhoc网络的体系结构。在介绍了信道接入协议的地位和作用后,对Adhoc网络特有的信道共享方式、隐终端和暴露终端问题进行了介绍和分析。文章把Adhoc网络的信道接入协议划分成基于单信道、双信道和多信道三类,最后给出了Adhoc网络信道接入协议的发展动向。     

基于可靠UDP的卫星IP网关设计

TCP是面向连接的可靠点到点协议,但是由于卫星网络中典型的长延时、高误码率以及非对称带宽的特点,导致TCP通过宽带卫星网络时,信道利用率非常低。可靠UDP协议基于标准UDP协议并在应用中增加窗口、应答和重传算法来实现。网关采用该协议将TCP连接分段,在应用中明显地改善了TCP在宽带卫星信道上传输的性能,增加TCP的信道利用率。     

基于强化学习的802.11ax上行链路调度算法

随着物联网(IoT)时代的到来,无线网络饱和的问题已经越来越严重。为了克服终端密集接入问题,IEEE标准协会(IEEE-SA)制定了无线局域网的最新标准—IEEE 802.11ax。该标准使用正交频分多址(OFDMA)技术对无线信道资源进行了更细致的划分,划分出的子信道被称为资源单元(RU)。为解决密集用户环境下802.11ax 上行链路的信道资源调度问题,该文提出一种基于强化学习的RU调度算法。该算法使用演员-评论家(Actor-Critic)算法训练指针网络,解决了自适应RU调度问题,最终合理分配RU资源给各用户,兼具优先级和公平性的保障。仿真结果表明,该调度算法在IEEE 802.11ax上行链路中比传统的调度方式更有效,具有较强的泛化能力,适合应用在密集用户环境下的物联网场景中。     

基于DAMA卫星系统的IP接入设计

TCP协议是面向连接的网络传输协议,当其应用在信道资源按需分配(DAMA)的卫星系统中时,TCP连接开始时所需的卫星链路并不存在,从而会导致TCP连接建立的失败。IP接入控制器配置在IP网络、卫星信道及网络管理设备之间,通过IP过滤、IP欺骗等方法将TCP数据转化为申请信令。解决了TCP业务的传输与卫星信道按需分配的匹配问题。     

BIPR: a new TCP variant over satellite networks

Standard TCP perform poorly in satellite networks since the long delay, high bit error ratio and other characters. A new TCP variant, called BIPR for satellite networks is presented in this paper. Using the binary increase of window growth function, long bandwidth-delay product can be overcome, while probe method is also adopted in BIPR for conquer the high bit error rates in satellite links. Simulation results show that good performances in terms of throughput, link utilization and RTT fairness can be achieved in satellite networks using our method.     

Analysis of TCP performance on multi-hop wireless networks: A cross layer approach

In Multi-Hop Wireless Networks (MHWNs), wireless nodes cooperate to forward traffic between end points that are not in direct communication range. Specifically, traffic is forwarded from a source towards its destination through intermediate nodes that form a wireless multi-hop chain. Researchers have studied the performance of TCP over chains discovering properties such as how the number of hops reduces chain throughput as neighboring links contend for the shared medium. Moreover, the presence of hidden terminals has also been shown to negatively affect performance of example chains. In this paper, we leverage recent characterization of how competing wireless links interact to develop an in-depth analysis of TCP performance over wireless chains. In particular, there are a number of possible modes of interference between competing links with distinct implications on performance and fairness; to our knowledge, this is the first work that studies the impact of these different modes on TCP chain performance. We classify chains according to interference modes considering both the forward (data) and reverse (acknowledgment) traffic. Chain geometry limits the types of chains that arise most frequently in practice. We evaluate TCP performance over the most frequently occurring chain types and observe significant performance differences between chains that have the same hop count. Different four-hop chains, for example, show a throughput difference of up to 25% and a retransmission overhead difference of over 90%. We discuss the implications of these differences on network performance: specifically, route instability and bandwidth usage generated. We extend this analysis to two single-hop TCP flows and quantify the effect of interference interactions between two flows. This study is a first step towards completely understanding the performance of multiple TCP flows over multiple hops in a MHWN.     

TCP Throughput Enhancement over Wireless Mesh Networks

TCP is the predominant technology used on the Internet to support upper layer applications with reliable data transfer and congestion control services. Furthermore, it is expected that traditional TCP applications (e.g., Internet access) will continue to constitute the major traffic component during the initial deployment of wireless mesh networks. However, TCP is known for its poor throughput performance in wireless multihop transmission environments. For this article, we conducted simulations to examine the impact of two channel interference problems, the hidden terminal and exposed terminal, on TCP transmissions over wireless mesh networks. We also propose a multichannel assignment algorithm for constructing a wireless mesh network that satisfies the spatial channel reuse property and eliminates the hidden terminal problem. The simulation results demonstrate the effectiveness of the proposed approach in improving the performance of TCP in wireless multihop networks.     

Enhancing Fairness and Throughput of TCP in Heterogeneous Wireless Access Networks

Most of the recent research on TCP over heterogeneous wireless networks has concentrated on differentiating between packet drops caused by congestion and link errors, to avoid significant throughput degradations due to the TCP sending window being frequently shut down, in response to packet losses caused not by congestion but by transmission errors over wireless links. However, TCP also exhibits inherent unfairness toward connections with long round-trip times or traversing multiple congested routers. This problem is aggravated by the difference of bit-error rates between wired and wireless links in heterogeneous wireless networks. In this paper, we apply the TCP Bandwidth Allocation (TBA) algorithm, which we have proposed previously, to improve TCP fairness over heterogeneous wireless networks with combined wireless and wireline links. To inform the sender when congestion occurs, we propose to apply Wireless Explicit Congestion Notification (WECN). By controlling the TCP window behavior with TBA and WECN, congestion control and error-loss recovery are effectively separated. Further enhancement is also incorporated to smooth traffic bursts. Simulation results show that not only can the combined TBA and WECN mechanism improve TCP fairness, but it can maintain good throughput performance in the presence of wireless losses as well. A salient feature of TBA is that its main functions are implemented in the access node, thus simplifying the sender-side implementation.     

Performance evaluation of TCP extensions on ATM over high bandwidthdelay product networks

Practical experiments in a satellite network environment assist in the design and understanding of future global networks. This article describes the practical experiences gained from TCP/IP on ATM networks over a high-speed satellite link and presents performance comparison studies of such networks with the same host/traffic configurations over local area and wide area networks. These comparison studies on the LAN, WAN, and satellite environments increase our understanding of the behavior of high-bandwidth networks. NASA's Advanced Communications Technology Satellite (ACTS), with its special characteristics and high data rate satellite channels, and the ACTS ATM Internetwork (AAI) were used in these experiments to deliver broadband traffic. Network performance tests were carried out using application-level software (Netspec) on SONET OC-3 (155.52 Mb/s) satellite links. Finally, we experimentally study the performance, efficiency, fairness, and aggressiveness of TCP Reno, TCP New Reno, and TCP SACK end hosts on ATM networks over high BDP networks     

一种异构网络TCP拥塞控制算法

针对互联网中端对端带宽、时延和丢包率等的差异性日益加剧,导致TCP传输性能严重退化,该文提出一种链路自适应TCP拥塞控制算法(INVS)。INVS在拥塞避免阶段初期采用基于指数函数的凸窗口增长函数,以提高链路利用率;在窗口增长函数中引入了自适应增长因子实现窗口增长速率与链路状态相匹配;采用了自适应队列门限的丢包区分策略以提高无线环境下TCP的性能。性能分析和评估表明,INVS提高了TCP拥塞控制算法的吞吐量、公平性、链路利用率和RTT公平性。     

基于网络利用率最大化来提高无线Mesh网络中TCP协议的传输性能

In Wireless Mesh Networks (WMNs), the performance of conventional TCP significantly deteriorates due to the unreliable wireless channel. To enhance TCP performance in WMNs, TCP/LT is proposed in this paper. It introduces fountain codes into packet reorganization in the protocol stack of mesh gateways and mesh clients. Furthermore, it is compatible with conventional TCP. Regarded as a Performance Enhancement Proxies (PEP), a mesh gateway buffers TCP packets into several blocks. It simultaneously processes them by using fountain encoders and then sends them to mesh clients. Apart from the improvement of the throughput of a unitary TCP flow, the entire network utility maximization can also be ensured by adjusting the scale of coding blocks for each TCP flow adaptively. Simulations show that TCP/LT presents high throughput gains over single TCP in lossy links of WMNs while preserving the fairness for multiple TCPs. As losses increase, the transmission delay of TCP/LT experiences a slow linear growth in contrast to the exponential growth of TCP.     

Active Queue Management for Fair Resource Allocation in Wireless Networks

This paper investigates the interaction between end-to-end flow control and medium access control (MAC)-layer scheduling on wireless links. We consider a wireless network with multiple users receiving information from a common access point; each user suffers fading and a scheduler allocates the channel based on channel quality but is subject to fairness and latency considerations. We show that the fairness property of the scheduler is compromised by the transport-layer flow control of transmission control protocol (TCP) New Reno. We provide a receiver-side control algorithm, CLAMP, that remedies this situation. CLAMP works at a receiver to control a TCP sender by setting the TCP receiver's advertised window limit, and this allows the scheduler to allocate bandwidth fairly between the users.     

JTCP: jitter-based TCP for heterogeneous wireless networks

Transmission control protocol (TCP), a widely used transport protocol performs well over the traditional network which is constructed by purely wired links. As wireless access networks are growing rapidly, the wired/wireless mixed internetwork, a heterogeneous environment will get wide deployment in the next-generation ALL-IP wireless networks. TCP which detects the losses as congestion events could not suit the heterogeneous network in which the losses will be introduced by higher bit-error rates or handoffs. There exist some unsolved challenges for applying TCP over wireless links. End-to-end congestion control and fairness issues are two significant factors. To satisfy these two criteria, we propose a jitter-based scheme to adapt sending rates to the packet losses and jitter ratios. The experiment results show that our jitter-based TCP (JTCP) conducts good performance over the heterogeneous network.     

Basestation flow control for wired to wireless networks

With the exponential growth of the internet, wireless networks such as satellite networks are becoming increasingly popular. The characteristics of satellite networks such as long latency, large delay-bandwidth product, high bit error rate over satellite links and variable round trip time, severely degrade TCP/IP performance. At the conjunction of the satellite link and the fixed link, the basestation, the difference in capacity between the satellite link and the fixed link causes the basestation to experience congestion losses that adversely impact TCP performance. We propose a technique that substantially reduces the congestion at the base station and enforces fairness among the TCP connections that are sharing the satellite link. The technique does not require any change in the TCP sender or the receiver. The stability of our algorithm is analytically proven and its performance is evaluated using ns-2 simulations. Preliminary results yield almost a null congestion loss rate, a 60% decrease in average queue length, and more than 30% increase in the throughput. Fairness is well enforced.