Average-value analysis of 802.11 WLANs with persistent TCP flows

In this letter we develop an average-value analysis of the TCP performance in 802.11 WLANs. Our model characterizes the equilibrium conditions of the network, and this method yields a simple, yet precise, estimate of the throughput obtained by persistent TCP flows. Via simulations we study the accuracy of the model predictions.     

光网络中的TCP混沌特性仿真分析

为了研究OBS网络的TCP非线性行为特性,本文利用Markov链模型,通过计算TCP窗口序列的Lyapunov指数,分析了影响TCP混沌特性的因素,以及这些因素对混沌特性的作用方式。仿真结果表明,OBS网络的TCP窗口非线性变化行为具有混沌特性,网络丢突发包率、突发包封装周期、TCP流速率以及最大拥塞窗口长度都会对TCP混沌特性产生影响。     

A high-performance and fair scheduler for the wireless network with a multi-state channel

This work presents a novel scheduler, exponential-rule fair queueing (EFQ), for fair scheduling in wireless networks with a multi-state channel. EFQ prefers flows destined to high-capacity channels to maintain a high throughput, and prefers flows with serious lagging to ensure excellent fairness. Simulation results demonstrate that EFQ not only provides higher throughput, but also maintains superior fairness, than existing schemes.     

TCP/IP协议处理器的多连接管理设计与实现

介绍了一种基于TCP/IP协议的可支持数千条连接的网络处理器,主要对TCP协议处理模块的多连接管理和切换做了重点的阐述.TCP协议是面向连接的协议,以往多连接的实现是将每一个连接作为操作系统的一个进程,由操作系统的进程管理程序统一进行调度.当需要将多连接用硬件来实现时,连接的切换就需要仿照操作系统的进程调度机制来进行.提出的多连接管理和切换的机制已经用Verilog HDL描述,并在Xilinx的Vertex4开发版上得到验证,结果证明此多连接管理和切换机制可以很好地支持数千条连接的同时运行,并在新型网络处理器中得到应用.     

基于FPGA的TCP/IP网络通信系统的设计与实现

针对纯软件实现网络通信时必须依赖于操作系统,且易受攻击的缺点,基于FPGA技术,通过控制W5500协议栈芯片的方式设计并实现一个TCP/IP网络通信系统。该系统加入网络断线自动重连功能,并在系统中使用CRC冗余差错检验对数据进行甄别,实现对非法数据的滤除。介绍系统的设计方案,并对系统进行了测试,系统的评价指标为丢帧率、误码率和传输速度。测试结果表明,该系统能对数据进行准确无误的传输,且数据传输速率较高。     

A method for calculating stationary queue distribution in a queuing system with flows of ordinary and negative claims and a bunker for superseded claims

A queuing system with one service unit and Poisson flows of positive and negative claims is considered. There is an infinite buffer for positive claims. A negative claim arriving at the system knocks out a positive claim waiting in the buffer and moves it to another infinite buffer (bunker). The claims from bunker are served with relative priority. If upon arrival of negative claim the buffer is empty, it leaves the system without affecting it. The service times for claims from buffer and bunker have exponential distributions with different parameters. A new method that provides efficient calculation of stationary distribution of the number of customers in buffer and bunker is proposed.     

Comprehensive performance analysis of a TCP session over a wireless fading link with queueing

A link model-driven approach toward transmission control protocol (TCP) performance over a wireless link is presented. TCP packet loss behavior is derived from an underlying two-state continuous time Markov model. The approach presented here is (to our knowledge) the first that simultaneously considers (1) variability of the round-trip delay due to buffer queueing; (2) independent and nonindependent (bursty) link errors; (3) TCP packet loss due to both buffer overflow and channel errors; and (4) the two modes of TCP packet loss detection (duplicate acknowledgments and timeouts). The analytical results are validated against simulations using the ns-2 simulator for a wide range of parameters; slow and fast fading links; small and large link bandwidth-delay products. For channels with memory, an empirical rule is presented for categorizing the impact of channel dynamics (fading rate) on TCP performance.     

Bayesian inference of network loss and delay characteristics with applications to TCP performance prediction

In large-scale dynamic communication networks, end systems cannot rely on the network itself to cooperate in characterizing its own behavior. This has prompted research activities on methods for inferring internal network behavior based on the external end-to-end network measurements. In particular, knowledge of the link losses and link delays inside the network is important for network management. However, it is impractical to directly measure packet losses or delays at every router. On the other hand, measuring end-to-end (from sources to destinations) losses or delays is relatively easy. We formulate the problems of link and delay estimation in a network based on end-to-end measurements as Bayesian inference problems and develop several Markov chain Monte Carlo (MCMC) algorithms to solve them. We show how these link loss and delay estimates can be used to predict point-to-point transfer control protocol (TCP) throughput in the network. We apply the proposed link loss and delay estimation algorithms, as well as the TCP throughput estimation algorithms, to data generated by the network simulator (ns-2) software and obtain good agreements between the theoretical results and the actual measurements.     

Performance evaluation of a queuing system with correlated packet-trains and server interruption

In this paper, we consider a practical queuing system with a finite number of input links and whose arrival process is correlated and consists of a train of a fixed number of fixed-length packets and a single server which is subjected to random interruptions. We model the server interruptions by a correlated Markovian on/off process with geometrically distributed on and off periods. We first derive an expression for the functional equation describing the transient evolution of this queuing system. This functional equation is then manipulated and transformed into a mathematical tractable form. This allows us to derive the probability generating function (pgf) of the system occupancy. From this pgf, closed-form expressions for various performance measures, such as mean and variance of system contents and customer delay can be derived. Finally, we illustrate our solution technique with some numerical examples, whereby we demonstrate the negative effect of correlation in the interruption process on the performance of the system. The paper presents new insights into the performance analysis of queuing systems with correlated arrivals and service interruption and it also covers some previously published results as a special case.     

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。     

A cross-layer analysis of TCP/link adaptation technologies over free-space optical links with Markov error model

This paper presents a comprehensive cross-layer framework on the performance of transmission control protocol (TCP) over a free-space optical (FSO) link, which employs automatic repeat request (ARQ) and adaptive modulation and coding (AMC) schemes. Not similar to conventional works in the literature of FSO, we conduct a Markov error model to accurately capture effects of burst errors caused by atmospheric turbulence on cross-layer operations. From the framework, we quantify the impacts of different parameters/settings of ARQ, AMC, and the FSO link on TCP throughput performance. We also discuss several optimization aspects for TCP performance.     

Traffic analysis of a local area network with a star topology

Two forms of fast circuit switching are modeled and studied through mathematical analysis and Monte Carlo simulation. The two examples described use the switching technique in an optical-fiber-based local area network with a star topology. The technique is compatible with time-division multiplexing techniques that are used for a range of traffic classes. Further, the technique trades transmission capacity for processing power, which is the critical limitation of the system. By means of a certain independence assumption, the first form of fast circuit switching is modeled as an M/G/1 queue. The results of the analysis show excellent agreement with simulation. The general result is that there is good system throughput, despite simplicity of processing. The second form, in which rather than first-come first-served the discipline is to search for a message whose destination queue is free, is studied by means of simulation alone. The results indicate an improved performance with a modest increase in processing power     

Design and analysis of a new self-routing network

A new self-routing network constructed from the sorting and the routing cells is proposed. The complexity of the new network is roughly twice as much as that of a pure banyan network. The new network can be viewed as an implementation of the load-sharing network which requires a very simple management. Its performance under uniform and nonuniform traffic models is analyzed for the unbuffered case. It is found that a higher degree of nonuniformity results in a better performance for certain forms of nonuniform traffic matrices. Simulations are performed to obtain the normalized throughputs and mean packet delays for the single-buffered case. Different from single-buffered pure banyan networks, the mean delay of high-traffic packets is smaller than that of low-traffic packets for a particular form of nonuniform traffic matrices. In addition to performance improvement, the new network is easy to diagnose. Some variations of the proposed network are also studied     

Performance analysis of a cellular network with multiple classes of calls

In this paper, we study a cellular mobile communications network with multiple cells and multiple classes of calls. The different classes of calls have different call holding times and residence time distributions. We consider a protocol mechanism under which a blocked call in a cell is either disconnected from the network or is deemed as a handoff call in a neighboring cell. Under this protocol, we prove that the stationary distribution of this cellular mobile network has a product form. This allows us to derive explicit expressions for handoff rates of each class of calls from one cell to another and the disconnecting probabilities for each class of new and handoff calls. Our numerical results show how these measures depend on the mobility of the mobile terminals in each cell and on the numbers of reserved channels.     

Performance analysis of a wireless ad hoc network with QoS support

A wireless ad hoc multihop network is introduced and protocols for the air interface are described and evaluated. Ad hoc networks can be realized due to the ability of stations to route connections according to the current meshing of the network. The decentrally organized network is able to guarantee the bandwidth contracted to a connection in a hidden station environment by means of contention-free data transmission, for both, channel and packet switched services, based on real channel connections. Channels are established and used for the duration of a so called train of data packets, released when the train ends and re-established when the next train arrives. To guarantee available capacity of the network for the re-establishment of a connection and to guarantee the quality of service needed for a wireless extension of a fixed ATM network, connection admission control is applied considering the overall interference situation and the current meshing of the stations in the network.For the purpose of realistic and reliable performance analysis a simulation tool appropriate for the investigation of the proposed network is introduced, and performance results for the proposed protocols are given by means of event-driven simulation studies in example scenarios. The simulated protocols have been formally specified in SDL, translated to C++, and embedded into a simulation environment.     

The performance of TCP/IP for networks with high bandwidth-delayproducts and random loss

This paper examines the performance of TCP/IP, the Internet data transport protocol, over wide-area networks (WANs) in which data traffic could coexist with real-time traffic such as voice and video. Specifically, we attempt to develop a basic understanding, using analysis and simulation, of the properties of TCP/IP in a regime where: (1) the bandwidth-delay product of the network is high compared to the buffering in the network and (2) packets may incur random loss (e.g., due to transient congestion caused by fluctuations in real-time traffic, or wireless links in the path of the connection). The following key results are obtained. First, random loss leads to significant throughput deterioration when the product of the loss probability and the square of the bandwidth-delay product is larger than one. Second, for multiple connections sharing a bottleneck link, TCP is grossly unfair toward connections with higher round-trip delays. This means that a simple first in first out (FIFO) queueing discipline might not suffice for data traffic in WANs. Finally, while the Reno version of TCP produces less bursty traffic than the original Tahoe version, it is less robust than the latter when successive losses are closely spaced. We conclude by indicating modifications that may be required both at the transport and network layers to provide good end-to-end performance over high-speed WANs     

Reliability and performance analysis of a modular multistage interconnection network

This paper introduces a class of cost-effective fault-tolerant multistage interconnection networks known as modular networks (MNs). With the help of reliability and cost analysis, we showed that MNs perform more reliably and are more cost-effective than most other previously proposed fault-tolerant networks. Performance analysis of the MNs has also been carried out under both fault-free and fault-present conditions; we showed that MNs provide a higher probability of acceptance than those of their counterpart unique-path networks and that the performance does not degrade too much in the presence of faults.     

Simulation-based analysis of a multi-hop integrated UMTS and WLAN network

The next generation communication networks will comprise of third-generation (3G) and fourth-generation (4G) cellular and multi-hop ad hoc networks. In particular, the Universal Mobile Telecommunications System (UMTS) and the IEEE 802.11 ad hoc networks will play a significant role. The UMTS can provide Internet service in wide areas with excellent mobility support while IEEE 802.11 can provide high speed last hop connectivity in indoor environment. The performance of the offered end-to-end TCP connection when these two different technologies come together to serve the users is an important aspect to be studied. In this paper, we build an analytical model to model the complete process of TCP packet transfer over this integrated network. The delay and end-to-end throughput are modeled. We also verify the simulation results considering the usual error rate in UMTS channels. Our analytical results match well with the simulation models that are widely used. Apart from modeling the Internet connectivity, our model can be used for multitude of tasks, such as gateway selection, resource reservation, etc., in the next generation cellular multi-hop networks.