In traditional operating systems, modifying the network protocol code is a tedious and error-prone task, largely because the networking stack resides in the kernel. For this reason, among others, many have proposed moving the networking stack to user-level. Unfortunately, implementations of this design have never entered widespread use due to the impractical requirements they place on the user: either the kernel or applications must be modified; or code cannot be moved seamlessly between the user-level and kernel stacks. In this paper, we present Alpine, a user-level networking infrastructure free from these drawbacks. Alpine supports a FreeBSD networking stack on top of a Unix operating system. It is freely available as source code. In this paper, we discuss the challenges we faced in virtualizing the FreeBSD networking stack without compromising on kernel, networking stack, and application compatibility. We then show how Alpine is effective at easing the burden of debugging and testing protocol modifications or new network protocols. In our experience, Alpine can reduce the overhead of modifying a protocol from hours to minutes. 1

Transparent Layer-4 proxies are being widely deployed in the current Internet to enable a vast variety of applications. These include Web proxy caching, transcoding, service differentiation, and load balancing. To ensure that all IP packets of an intercepted TCP connection are seen by the intercepting transparent proxy, they must sit at focal points in the network. Translucent Proxying of TCP (TPOT) overcomes this limitation by using TCP options and IP tunneling to ensure that all IP packets belonging to a TCP connection will traverse the proxy that intercepted the first packet. This guarantee allows the ad-hoc deployment of TPOT proxies anywhere within the network. No extra signaling support is required for its correct functioning. In addition to the advantages TPOT proxies offer at the application level, they also usually improve the throughput of intercepted TCP connections. In this paper we discuss the TPOT protocol, explain how it enables various applications, describe a prototype...

Abstract—In wide-area Grid computing, geographically distributed computational resources are connected for enabling efficient and large-scale scientific/engineering computations. In the wide-area Grid computing, a data transfer protocol called GridFTP has been commonly used for large file transfers. GridFTP has the following features for solving problems of the existing TCP. First, for accelerating the start-up in TCP’s slow start phase and achieving high throughput in TCP’s congestion avoidance phase, multiple TCP connections can be established in parallel. Second, according to the bandwidth-delay product of a network, the TCP socket buffer size can be negotiated between GridFTP server and client. However, in the literature, sufficient investigation has not been performed either on the optimal number of TCP connections or the optimal TCP socket buffer size. In this paper, we therefore quantitatively investigate the optimal parameter configuration of GridFTP in terms of the number of TCP connections and the TCP socket buffer size. We first derive performance metrics of GridFTP in steady state (i.e., goodput and packet loss probability). We then derive the optimal parameter configuration for GridFTP and quantitatively show performance limitations of GridFTP through several numerical examples. We also demonstrate validity of our approximate analysis by comparing simulation results with analytic ones.

On September 26, 1999, a musical performance, taking place at McGill University, was transmitted to an audience at New York University, over the Internet. While Internet streaming audio technologies have been in use for several years, what made this event unique was the audience's experience of uninterrupted, intermediate quality, multichannel audio (AC-3). In order to achieve this result, a custom system was developed employing both TCP and UDP protocols, and providing its own buffering and retransmission algorithms. The motivation for this approach is explored, and experiments justifying the decisions made are explained. = Appeared in Journal of the Audio Engineering Society,July-August, 2000. 2 1 Introduction The growth of the Internet has not only reshaped our work lives, but, in recent years, has also begun to affect and redefine various areas of entertainment, in particular, that of music. Until the last decade, the idea of downloading music to one's home, at great convenienc...

Abstract-- The number of households and businesses using HFC cable networks for Internet access is rapidly approaching 20million in the United States. The cable industry has standardized on a single MAC and physical layer standard, the Data Over Cable System Interface Specification (DOCSIS). We have implemented a simulation model of the DOCSIS 1.1/2.0 MAC and physical layer using the ‘ns ’ simulation package. In this paper we provide analytic and live network evidence that the simulation model is correct. To demonstrate the model, we provide the results of a brief simulation-based performance evaluation designed to provide insight as to how a best effort VoIP service (e.g., Vonage) performs under varying traffic loads compared to a VoIP service that utilizes DOCSIS QoS mechanisms.

TCP was designed and tuned to work well on networks where losses are mainly congestion losses. The performance of TCP decreases dramatically when a TCP connection traverses a wireless link on which packets may be lost due to wireless transmission errors. Explicit Congestion Notification (ECN) is known as an effective mechanism that can be used with Active Queue Management (e.g. RED) to control congestion on wired networks. ECN is used by routers to signal incipient congestion to end points. We evaluate the ability of ECN signals as a tool to distinguish between congestion losses and wireless losses. The occurrence of an ECN signal is a bad predictor of imminent congestion losses. We conclude that when TCP senders are responsive to ECN signals, congestion losses appear to be as random as wireless losses. Based on this observation, we propose a simple technique, TCP-Eaglet, to improve TCP over wireless for ECN responsive flows. Simulations results show an improvement in throughput of up to 60%.

Abstract- The deployment of data-over-cable broadband Internet access continues to unfold throughout the world. While there are competing technologies, the Data over Cable (DOCSIS) 1.1/2.0 effort is emerging as the single standard. There has been little research exploring the impact that the DOCSIS 1.1/2.0 MAC and physical layers has on the performance of Internet applications. We have developed a model of DOCSIS using the ‘ns ’ simulation package. In this paper we present the results of a performance analysis that we have conducted using the model. The contribution of our work is twofold. First, we provide insight into the interaction between the DOCSIS MAC protocol and web traffic. Our analysis suggests that DOCSIS does not efficiently support downstream web browsing. Second, we show how a DOCSIS system is vulnerable to a denial of service attack by a hacker who exploits the interaction between the DOCSIS MAC layer and TCP. We show that downstream rate control is not sufficient to avoid the vulnerability.

Abstract- Since the first community antenna television (CATV) system was deployed in 1948, cable technology has advanced at an astounding rate. Today, multiple service providers (MSOs) are competing with telephone companies to deliver the long sought ‘triple play ’ of voice, video and data to residential and business premises. Upstream data rates have progressed from dial-up speeds to 10Mbps and to 100s of Mbps in the near future. While there are competing standards, the Data over Cable Service Interface Specification (DOCSIS) has emerged as the single MAC and physical layer standard. We have developed a model of DOCSIS using the ‘ns ’ simulation package. In this tutorial paper we provide a detailed presentation of the DOCSIS protocol. To provide a deeper understanding of DOCSIS, we present the results of a simulation analysis focusing on the impact that DOCSIS has on TCP applications. The objectives of this tutorial are: 1)to provide an overview of the DOCSIS protocol; 2)to present the ‘ns ’ simulation model; 3)to present preliminary upstream contention and downstream transmission queuing network models (QNMs).

This thesis presents practical studies of the TCP performance problems caused by the asymmetric nature of ADSL connections. Previously, it has been shown on other types of asymmetric links that TCP throughput may be reduced due to a variable and imperfect ACK feedback. The upstream capacity of ADSL products in general does not disturb the ACK feedback mechanism, but we analyze and document that TCP traffic across ADSL in fact is affected by the asymmetric nature of ADSL, when utilizing the upstream capacity. For a single user ADSL installation it is manageable to avoid upstream congestion, but for larger networks, connected to the Internet by ADSL, the rise of peer-to-peer file sharing applications may result in a permanently congested upstream link. The thesis provides evidence that the achievable downstream throughput is reduced significantly in case of a saturated upstream link. Saturation of the upstream link introduces a high queueing delay that effectively renders the connection useless for interactive and other delay-sensitive applications (like VoIP).

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