使用EHN-HP机制提高移动切换中TCP性能

移动通讯技术的发展促使传统有线互联网向无线移动网络延伸.TCP协议是现在互联网上使用最为广泛的端到端可靠传输协议,但TCP协议是在有线链路基础上设计的,直接在无线移动网络上使用TCP协议会造成TCP性能的下降.本文详细分析了移动切换对TCP协议造成的影响,比较并分析现有的几种解决方案,针对切换对TCP造成的影响提出了EHN-HP机制.EHN-HP机制在现有的TCP协议上进行改进,增加了切换处理机制(Handoff Process),通过网络模拟器的模拟结果表明,EHN-HP机制有效的改善了TCP协议在切换过程中的性能.     

WiFi中多AP间快速切换的研究与实现

目前,WiFi已经成为了高速无线局域网的主要标准并且得到了广泛的应用。鉴于WiFi网络接入点（AP）覆盖范围小、移动用户需要频繁切换的特点,文中提出了多AP连接和嗅探扫描两种技术来实现多AP间的快速切换。多AP连接通过同时和多个AP保持通信切实保障了通信连续性,而嗅探扫描为更有效地获取周围AP信息提供了指导性方法。实验表明这些技术有效地加快了切换的速度,有效保障了用户的QoS。     

Linux环境下基于TCP的Socket编程浅析

Socket适用于同一台计算机上的进程间通信，同时也适用于网络环境中的进程间通信。他已成为当前许多操作系统的网络API，也是网络操作系统中必不可少的基础功能。因特网为网络中的应用提供了2种类型的服务：由TCP协议提供的面向连接服务和由UDP协议提供的无连接服务。随着Linux操作系统的不断推广，Linux环境下的Socket开发和研究一直是人们关注的热点。文章介绍了Linux平台下的Socket及其在TCP协议下的编程原理，并通过一个用Java编写的基于TCP的客户／服务器程序，描述了网络中不同主机上的两个进程之间的Socket通信机制。     

基于TCP协议的网络管理系统设计与实现

目前,网络管理技术主要有两种:基于TCP/IP网络的简单网络管理协议SNMP和由ISO开发的公共管理信息协议CMIP.SNMP使用了提供无连接服务的传输层协议(UDP).其特点是不保证数据接收的顺序性、完整性和可靠性,不适于较复杂的电信网络的管理.CMIP协议使用的是面向连接的方式,但是需要OSI七层协议栈的支持,实现起来较复杂,因此尚未得到广泛使用. 　　虽然Intemet的有关组织提出了公共管理信息服务与协议(CMOT),以在TCP/IP协议上实现CMIS服务,但这是一种过渡解决方案,许多网络管理系统开发商并不想花费时间实现一个过渡性的方案,因此,CMOT也没有得到发展.……     

吉比特网络中TCP数据流重组和交付的ASIC实现

随着光纤网络的发展，高速网络中限制终端用户到终端用户之间的瓶颈已不再是网络带宽，而是对网络中TCP流的中止。为了使终端用户能够享受广阔带宽的资源，就必须把TCP协议的处理从主CPU中卸载出，用ASIC来实现。本文给出了如何实现TCP数据流重组和交付的方法：首先对该协议处理器进行功能模块划分，然后进行仿真、综合和时序分析等。分析结果表明，协议处理器处理TCP数据包的能力达到了3．2Gbit网络的线速度。     

基于网络处理器的队列管理和队列调度分析

对利用网络处理器实现队列操作进行了研究.通过队列管理和队列调度在IntelIXP2805网络处理器上的实现,验证了服务质量机制在网络处理器平台上的可行性.实践证明,队列操作基本满足对数据包线速处理的要求,网络处理器硬件资源利用率较高.     

垂直切换中避免TCP连接吞吐量下降方法的比较

移动性管理被用来解决异构网络的无缝切换和服务的连续性。因而,切换时正在进行的TCP连接可以在移动终端从一个接入网络切换到另一接入网络时保持存活。如果一个新的TCP连接被建立,它将从慢启动阶段开始,如果是原来的连接被转移则TCP连接将由于丢包进入拥塞避免阶段,两者都会造成吞吐量的下降。为了解决吞吐量下降的问题,文献中提出了各种解决方案,文章讨论了一些基于端到端的解决方案,同时根据一些准则对其进行比较。     

网络切换对TCP吞吐量和公平性的影响分析

无线移动网络的发展日新月异.TCP协议是目前互联网上使用的最为广泛的端到端可靠传输协议,但其应用在无线网络上的时候,TCP性能下降明显.文中详细分析了TCP移动网络的切换对TCP造成影响的几个重要方面.最后通过在NS2上进行实验揭示了对多个TCP流公平性的影响,即切换后RTT越小的TCP流的吞吐量增长的越快,同时静态链路会夺取无线链路的链路资源.     

多频带无线通信系统的多连接实现方案

本文提出了多频带无线通信系统中包括虚拟多连接和异频多连接等两种多连接模式的实现方案,并将后者进一步划分为多业务多连接和单业务多连接等两种场景。并且,从数据包处理流程、调度结构、HARQ过程以及频带间切换等方面对上述多连接模式的实现进行分析和比较,最后得出相应的结论。     

高速网络TCP/IP减荷的研究

近十年来,随着网络技术的发展,网络带宽迅速增长,而同期CPU的性能未得到相应的提高.在吉比特网络下,网络终端CPU处理TCP/IP协议的能力已经成为限制网络应用的瓶颈.为了使终端用户能充分利用广阔的带宽资源,需要提高网络终端的协议处理能力.文中基于FPGA的硬件设计,将原来由软件完成的IP层协议功能完全卸载出来,向CPU提供硬件支持.并且通过功能仿真、综合后仿真、布局布线后仿真验证了设计的可行性,由静态时序分析可知,协议处理器的时钟频率可达50 MHz,处理IP数据流的能力可以达到1.6 Gb/s的网络线速度.     

Design and Implementation of Embedded Transmission Control Protocol/Internet Protocol Network Based on System-on-programmable Chip

A scheme of transmission control protocol/Internet protocol（TCP/IP） network system based on system-on-programmable chip（SOPC） is proposed for the embedded network communication. In this system, Nios processor, Ethernet controller and other peripheral logic circuits are all integrated on a Stratix Ⅱ field programmable gate array （FPGA） chip by using SOPC builder design software. And the network communication is realized by transplanting MicroC/OS Ⅱ （uC/OS Ⅱ ） operation system and light weight Internet protocol（LwIP）. The design idea, key points and the structures of both software and hardware of the system are presented and ran with a telecommunication example. The experiment shows that the embedded TCP/IP network system has high reliability and real-time performance.     

Efficient user-space protocol implementations with QoS guaranteesusing real-time upcalls

Two important requirements for protocol implementations to be able to provide quality of service (QoS) guarantees within the endsystem are: (1) efficient processor scheduling for application and protocol processing and (2) efficient mechanisms for data movement. Scheduling is needed to guarantee that the application and protocol tasks involved in processing each stream execute in a timely manner and obtain their required share of the CPU. We have designed and implemented an operating system (OS) mechanism called the real-time upcall (RTU) to provide such guarantees to applications. The RTU mechanism provides a simple real-time concurrency model and has minimal overheads for concurrency control and context switching compared to thread-based approaches. To demonstrate its efficacy, we have built RTU-based transmission control protocol (TCP) and user datagram protocol (UDP) protocol implementations that combine high efficiency with guaranteed performance. For efficient data movement, we have implemented a number of techniques such as: (1) direct movement of data between the application and the network adapter; (2) batching of input-output (I/O) operations to reduce context switches; and (3) header-data splitting at the receiver to keep bulk data page aligned. Our RTU-based user-space TCP/Internet protocol (TCP/IP) implementation provides bandwidth guarantees for bulk data connections even with real-time and “best-effort” load competing for CPU on the endsystem. Maximum achievable throughput is higher than the NetBSD kernel implementation due to efficient data movement. Sporadic and small messages with low delay requirements are also supported using reactive RTUs that are scheduled with very low delay. We believe that ours is the first solution that combines good data path performance with application-level bandwidth and delay guarantees for standard protocols and OSs     

Connection establishment in high-speed networks

Protocols for establishing, maintaining, and terminating connections in packet-switched networks have been studied, and numerous standards have been developed to address this problem. The authors reexamine connection establishment in the context of a high-speed packet network, introduce a protocol for connection establishment/takedown that is appropriate for such a network, and explain its advantages over previously proposed protocols. The main features of the proposed protocol are: fast bandwidth reservation in order to avoid as much as possible reservation conflicts, guaranteed release of the reserved bandwidth even under modal and link failures, and soft recovery from processor failures, which allows the maintenance of existing connections under processor failure provided the switch and links do not fail. The underlying model that is used is the PARIS/plaNET network, but the protocol can be adapted to other fast packet networking architectures as well     

Steady-State analysis of a split-connection scheme for Internet access through a wireless terminal

TCP does not perform well in a connection that includes a lossy wireless link. Techniques intended to improve the performance of TCP for such connections can be grouped into three categories: end-to-end, link layer and split-connection approaches. Some simulations and experimental results indicate that split-connection protocols yield better performance than the other two approaches. Although analytical modeling of the end-to-end and link-layer approaches has been presented, no comparable performance analysis for split-connection protocols has been reported previously. In this paper, a stochastic model is developed and used to analyze the performance of a class of split-connection protocols which deploy TCP on the wire-line network and a light-weight transport protocol on the wireless final hop. The final hop is provided by a digital TDMA cellular system. The condition of heavy source traffic to the wireless terminal is considered. The model relates the throughput and some useful auxiliary performance measures to key system parameters such as propagation delays, the base-station buffer size, the ARQ protocol and channel-error process of the wireless link. The usefulness of the analysis is illustrated by its application to the problem of sizing the TCP receiving buffer in a base station.     

TCP/IP协议的ASIC设计与实现

文章介绍了一种TCP/IP协议族传输、处理TCP数据和IP数据报过程的ASIC设计-TCP/IP协议处理器的硬件实现。简单介绍了TCP/IP协议，着重介绍了TCP/IP协议处理器系统结构以及各模块设计。硬件实现的TCP/IP协议处理器提高了IP数据报的处理速度，更重要的是，将Internet网络数据传输从传统的依赖电子计算机系统的模式中解放出来，实现了脱离计算机系统环境建立Internet网络连接。     

An Internet friendly transport protocol for continuous media over best effort networks

In this paper, we design and evaluate an Internet friendly transport‐level protocol (IFTP) for solving the TCP‐friendly problem. IFTP has two modes of operation. In the standard mode, the IFTP connection faithfully emulates the behaviour of TCP in order to roughly obtain a bandwidth equal to that of a TCP connection. In the extended mode, a simple modification is used to grant QoS‐differentiated services to selected connections. Connections running in the extended mode can get enhanced bandwidth while still emulating the general behaviour of TCP. We develop an analytical model for the congestion control mechanism of IFTP. We also derive analytically the amount of bandwidth that IFTP may be able to claim from TCP in ideal and non‐ideal environments. We evaluate IFTP through simulation and prove its TCP friendliness as well as provide performance results on some of the important metrics such as packet delay, delay jitter, packet loss and link utilization. Copyright © 2002 John Wiley & Sons, Ltd.     

Analysis and stochastic characterization of TCP flows

Since the most Internet services use TCP as a transport protocol there is a growing interest in the characterization of TCP flows. However, the flow characteristics depend on a large number of factors, due to the complexity of the TCP. As a result, the TCP characteristics are normally studied by means of simulations or controlled network setups. In this paper we propose a TCP characterization based on a generic model based of stochastic flow with burstiness and throughput ((σ,ρ)-constrains), which is useful in order to characterize flows in atm and other flow-switched networks. The model is obtained through extensive analysis of a real traffic trace, comprising an approximate number of 1,500 hosts and 1,700,000 TCP connections. The results suggest that TCP connections in the wide area Internet have low throughput while the packet bursts do not suffer an exponential increase, as indicated by the slow-start behavior. On the other hand, the impact of the connection establishment phase is striking. We note that the throughput of the TCP flow is approximately half the throughput which is obtained in the data transfer phase, namely after the connection has been established.     

ATCP: TCP for mobile ad hoc networks

Transport connections set up in wireless ad hoc networks are plagued by problems such as high bit error rates, frequent route changes, and partitions. If we run the transmission control protocol (TCP) over such connections, the throughput of the connection is observed to be extremely poor because TCP treats lost or delayed acknowledgments as congestion. We present an approach where we implement a thin layer between Internet protocol and standard TCP that corrects these problems and maintains high end-to-end TCP throughput. We have implemented our protocol in FreeBSD, and we present results from extensive experimentation done in an ad hoc network. We show that our solution improves the TCP's throughput by a factor of 2-3     

Transport protocols for Internet-compatible satellite networks

We address the question of how well end-to-end transport connections perform in a satellite environment composed of one or more satellites in geostationary orbit (GEO) or low-altitude Earth orbit (LEO), in which the connection may traverse a portion of the wired Internet. We first summarize the various ways in which latency and asymmetry can impair the performance of the Internet's transmission control protocol (TCP), and discuss extensions to standard TCP that alleviate some of these performance problems. Through analysis, simulation, and experiments, we quantify the performance of state-of-the-art TCP implementations in a satellite environment. A key part of the experimental method is the use of traffic models empirically derived from Internet traffic traces. We identify those TCP implementations that can be expected to perform reasonably well, and those that can suffer serious performance degradation. An important result is that, even with the best satellite-optimized TCP implementations, moderate levels of congestion in the wide-area Internet can seriously degrade performance for satellite connections. For scenarios in which TCP performance is poor, we investigate the potential improvement of using a satellite gateway, proxy, or Web cache to “split” transport connections in a manner transparent to end users. Finally, we describe a new transport protocol for use internally within a satellite network or as part of a split connection. This protocol, which we call the satellite transport protocol (STP), is optimized for challenging network impairments such as high latency, asymmetry, and high error rates. Among its chief benefits are up to an order of magnitude reduction in the bandwidth used in the reverse path, as compared to standard TCP, when conducting large file transfers. This is a particularly important attribute for the kind of asymmetric connectivity likely to dominate satellite-based Internet access     

NS2中TCP连接建立模拟的改进

传输控制协议(TCP, transmission control protocol)连接建立的“三次握手”过程中涉及对半连接表和连接表的管理。但是,已得到广泛应用的网络模拟器NS2对TCP连接建立过程只有一个形式的表示, 没有完整的具体实现。对此进行了改进, 为NS2增加了半连接表结构, 并将Linux内核管理半连接表的方式移植到了NS2中。仿真结果可清晰地看到TCP连接建立过程中半连接表变化, 从而满足TCP SYN洪泛攻击防控等研究中对TCP连接建立过程模拟的需要。