网络代理服务器的设计与实现

随着计算机网络技术的广泛应用,企业内部网络发展得非常迅速。防火墙作为一种网络安全技术的重要方法,有效地保护了企业内部网络的安全。该文主要对网络代理服务器进行了设计与研究,首先阐述了防火墙的功能,接着分析了代理服务器的工作原理,详细描述了执行流程,最后介绍了基于VB环境下,代理服务器的设计与实现方法。     

分布式防火墙与代理服务器技术相结合的安全性文件存取研究

本文研究以企业组织内部网络的文件安全性为范围,结合分布式防火墙技术在封包层次的过滤与控制功能,以及代理服务器在应用层次的存取分析与控制功能,辅以传统的SSL安全联机及VPN虚拟私有网络技术,并以使用者的应用为导向,来控制网络行为,以形成一个多层次的安全性文件存取机制。     

基于MINA框架的RTSP移动流媒体代理服务器设计与实现

该文设计了一个基于RTSP(Real Time Streaming Protocol)协议的移动流媒体代理服务器。基于该设计,作者在Apache MI-NA 2.0网络程序框架下实现了该代理服务器。该代理服务器可用于校园、酒店等公共热点环境,为具有WiFi功能的智能手机提供音视频接入服务。     

树上时延约束的代理服务器放置问题

该文考虑网络数据更新,需要控制代理服务器与目标服务器的距离时,树状网络上代理服务器的放置问题。利用二叉树结构和动态规划方法,得到了一个时间复杂度O(nhk)为多项式时间算法,其中n为网络结点数,k为代理服务器要放置的个数,h为树高。     

代理服务器的设计与实现

该文深入分析计算机网络领域的代理服务器的基本工作原理和功能,从代理数据转发功能着手对比分析了各种实现技术,根据选择性分析结果提出了IP层及以上的代理服务器的实现模型,实现了基于Winsock控件的代理服务器。     

思科岗前实训基地NAC网络准入控制的部署及实现

该文从广东科学技术职业学院思科岗前实训基地实际建设入手,介绍思科岗前实训基地NAC网络准入控制的部署及实现,并从实际应用提出一个完整思科岗前实训基地NAC网络准入控制建设方案。为构建可信的网络环境,应对身份认证及权限控制等安全问题,基于CISCO NAC技术在实际建设中实现了完备、高性能及高安全的网络准入控制系统。     

应用代理服务器实现网络管理

该文介绍了通过架设代理服务器,应用代理服务器,实现网络管理。在Linux系统中,应用Squid软件,实现代理服务,并设置相应的访问策略、查看访问日志,实现网络管理。同时介绍了利用虚拟机技术,架设代理服务器,可以灵活地应用于临时性、小规模的场所。     

基于代理的Web页访问语义过滤与内容重现

对Web页进行必要的、有效的内容过滤对于营造健康、安全的网络环境具有重要的意义。重现用户成功访问过的Web页内容,可以对网络访问进行事后监督,为过滤机制的完善提供相应数据。文中分析了Web页的访问流程,基于HTTP代理服务器,在应用层实现了对Web页的关键字过滤和基于语义的内容过滤,并通过将客户机成功访问过的Web页存储在代理服务器硬盘上,实现了内容重现。试验表明,语义过滤能较好地甄别文本的不同观点,准确度较单纯关键字过滤有明显提高。     

网络中时延受限的代理服务器放置问题

该文考虑网络数据更新,需要控制代理服务器与客户的距离时,网络中的代理服务器的放置问题。找到代理服务器的最优数量和放置位置,使网络中数据访问的总花费（包括数据读取和更新）最小。利用二叉树结构和动态规划方法,得到了一个时间复杂度O（n²）的多项式时间算法,其中n为网络结点数。     

基于代理的Web页访问语义过滤与内容重现

对Web页进行必要的、有效的内容过滤对于营造健康、安全的网络环境具有重要的意义。重现用户成功访问过的Web页内容，可以对网络访问进行事后监督，为过滤机制的完善提供相应数据。文中分析了Web页的访问流程，基于HTTP代理服务器，在应用层实现了对Web页的关键字过滤和基于语义的内容过滤，并通过将客户机成功访问过的Web页存储在代理服务器硬盘上，实现了内容重现。试验表明，语义过滤能较好地甄别文本的不同观点，准确度较单纯关键字过滤有明显提高。     

Loopback: exploiting collaborative caches for large-scale streaming

In this paper, we propose a Loopback approach in a two-level streaming architecture to exploit collaborative client/proxy buffers for improving the quality and efficiency of large-scale streaming applications. At the upper level we use a content delivery network (CDN) to deliver video from a central server to proxy servers. At the lower level a proxy server delivers video with the help of collaborative client caches. In particular, a proxy server and its clients in a local domain cache different portions of a video and form delivery loops. In each loop, a single video stream originates at the proxy, passes through a number of clients, and finally is passed back to the proxy. As a result, with limited bandwidth and storage space contributed by collaborative clients, we are able to significantly reduce the required network bandwidth, I/O bandwidth, and cache space of a proxy. Furthermore, we develop a local repair scheme to address the client failure issue for enhancing service quality and eliminating most required repairing load at the central server. For popular videos, our local repair scheme is able to handle most of single-client failures without service disruption and retransmissions from the central server. Our analysis and simulations have shown the effectiveness of the proposed scheme.     

Optimized streaming media proxy and its applications

Multimedia streaming is one of the most popular services on the current Internet. However, the major problem hinders streaming media applications is the network bandwidth. In this paper, we put forward a optimized streaming proxy system and think of utilizing it in peer-to-peer (P2P) applications. The main contribution of our proxy system is RTP segments splicing, prefix caching size determination and prefetching techniques, which are detailed discussed in this paper. By validating our implementation, the experimental results show that the streaming proxy can effectively contribute to reduce the server and backbone network load, thus achieve improved media quality and scalability. In addition, P2P network is a fascinate way for Internet resource sharing, many of researchers are devoting to research on P2P-based client communications. In our project, we make use of our proxy prototype into the streaming sharing over P2P network, each peer node just like a lightweight proxy between the server and the target peers. The real-time video sharing (RVS) system efficiently utilizes network bandwidth between peer clients through combining with our proxy as expected.     

Internet网络层代理服务器的设计

文章讨论了解决Internet地址不够用的网络层代理服务器的设计问题,给出了IP伪装源端口代理的原理,提出了采用环形列表法实现正、反代理变换.在设计代理服务器时,讨论了100M PCI总线以太网卡的开发,提出了采用环形缓冲区的非阻塞式网络数据处理方法,这种方法极大地提高代理服务器的可靠性与效率.文章最后指出代理服务器具有高的安全性.     

中石油企业网中代理服务器的安全性检测

在企业网中为了限制非授权用户访问企业网之外的资源,一般在代理服务器上进行IP地址或计算机MAC绑定.但是如果代理服务器的参数设置不合适,可能起不到限制非授权用户访问外网的作用.为了检测哪些代理服务器没有进行非授权用户IP或MAC限制,使用C++Builder 6.0的NMHTTP控件开发了一个局域网代理服务器检测程序....     

Proxy-assisted scalable periodic broadcasting of videos for heterogeneous clients

Periodic broadcasting (PB) is a scalable technique for providing video-on-demand services. It significantly reduces server input and output (I/O) and backbone network bandwidth requirements, but increases the clients’ need for storage space and network bandwidth. Traditional protocols assume homogeneous clients with identical resources. In practice, however, clients have very different bandwidths, which are usually not sufficient for video-on-demand service from a PB server. Existing work on heterogeneous clients has focused on devising broadcast schedules that cater to low-bandwidth clients; these schedules inevitably require additional backbone network bandwidth between the server and the clients. In this paper, we propose a scheme to significantly reduce the waiting time of all heterogeneous clients, without the need for any additional backbone bandwidth. This scheme uses a proxy buffer within video-on-demand systems using PB. In the proposed system, the server broadcasts a video using one of the traditional PB protocols. Simultaneously, the proxy receives the stream from the server and stores it in its local buffer, then broadcasts the stored data to the clients in its local network. Because the proxy provides extra, transparent channels to the server, clients are likely to reduce their reception bandwidth requirements through the use of efficient reception schedules using the extra channels.     

SMTVS:一种基于H.264的手机电视系统

手机电视系统必须能够适应网络和客户端的异构性、无线信道的多变性等特点.提出一种手机电视系统SMTVS,流媒体服务器在不同码率的H.264视频流之间进行切换以适应网络状况的变化;代理服务器之间构成一个内容分送网络,视频数据通过应用层组播的方式传输到各个代理服务器,降低了服务器的负载,提高了网络资源利用率;代理服务器接收到视频数据之后,针对无线链路的状况对数据进行处理后再发送到客户端,以适应最终用户的不同需求;客户端根据网络状况来动态调整播放速率,避免显示缓冲区下溢和上溢.通过流媒体服务器、代理服务器以及客户端的协作,实现了视频数据在无线信道上的自适应传输.     

Proxy-based hybrid cache management in Mobile IP systems

In this paper, we propose and analyze a proxy-based hybrid cache management scheme for client-server applications in Mobile IP (MIP) networks. We leverage a per-user proxy as a gateway between the server and the mobile host (MH) such that any communication between the MH and server must pass through the proxy. The proxy has dual responsibilities in our design. It keeps track of the current location of the MH by acting as a regional Gateway Foreign Agent (GFA) as in the MIP Regional Registration protocol for mobility management. The proxy is also responsible for cache consistency management and query processing on behalf of the MH. To reduce the network traffic, a threshold-based hybrid cache consistency management policy is applied. That is, when a data object is updated at the server, the server sends an invalidation report to the MH through the proxy to invalidate the cached data object, provided that the size of the data object exceeds the given threshold. Otherwise, the server sends a fresh copy of the data object through the proxy to the MH. We identify the best “threshold” value that would minimize the overall network traffic incurred due to mobility management, cache consistency management, and query processing, when given a set of parameter values characterizing the operational and workload conditions of the MIP network.     

Dynamic proxy-assisted scalable broadcasting of videos for heterogeneous environments

Periodic broadcasting (PB) is a scalable technique for providing video-on-demand services. It significantly reduces server I/O and backbone network bandwidth requirements at the expense of high storage space and high network bandwidth requirements for clients. Traditional protocols assume homogeneous clients with identical resources. Unfortunately, in practice clients have very different bandwidths, and these are usually insufficient to provide video-on-demand (VoD) service from a PB server. Existing work on heterogeneous clients has focused on devising broadcast schedules to cater to low-bandwidth clients, which inevitably requires an extra backbone network bandwidth between the server and the clients. In our previous work, we proposed to use proxies residing at the edge of backbone network to accommodate low bandwidth clients for PB-based VoD services. The server broadcasts a video using a PB protocol while the proxy receives and stores the data in its local buffer and broadcasts the stored data to the clients in its local network. It significantly reduces the waiting time of low-bandwidth clients without requiring any extra backbone bandwidth by using a proxy buffer and channels. However, although lots of PB protocols have been proposed, the scheme can be applied only to some old PB protocols based on a pyramid protocol. In this paper, we propose a proxy-assisted PB system that can be generally applied to almost all the existing PB protocols, by dynamically managing buffer space and channels in proxy servers. Thus, with our proposed system, PB VoD system can be optimized in terms of the resource usages in backbone networks, proxy servers, and clients, by adopting more suitable PB protocols.     

Reducing bandwidth requirement for delivering video over wide area networks with proxy server

Due to the high bandwidth requirement and rate variability of compressed video, delivering video across wide area networks (WANs) is a challenging issue. Proxy servers have been used to reduce network congestion and improve client access time on the Internet by caching passing data. We investigate ways to store or stage partial video in proxy servers to reduce the network bandwidth requirement over WAN. A client needs to access a portion of the video from a proxy server over a local area network (LAN) and the rest from a central server across a WAN. Therefore, client buffer requirement and video synchronization are to be considered. We study the tradeoffs between client buffer, storage requirement on the proxy server, and bandwidth requirement over WAN. Given a video delivery rate for the WAN, we propose several frame staging selection algorithms to determine the video frames to be stored in the proxy server. A scheme called chunk algorithm, which partitions a video into different segments (chunks of frames) with alternating chunks stored in the proxy server, is shown to offer the best tradeoff. We also investigate an efficient way to utilize client buffer when the combination of video streams from WAN and LAN is considered.     

Frame Selection for Dynamic Caching Adjustment in Video Proxy Servers

By caching video data, a video proxy server close to the clients can be used to assist video delivery and alleviate the load of video servers. We assume a video can be partially cached and a certain number of video frames are stored in the proxy server. In our setting, the proxy server is allowed to cache the passing data from the video server. A video provides several options (levels) in terms of bandwidth requirement over the server-proxy path. For each video, the proxy server decides to cache a smaller amount of data at a lower level or to accumulate more data to reach a higher level. The proxy server can dynamically adjust the cached video data by choosing an appropriate level based on the network condition or the popularity of the video. We propose a frame selection scheme, Dynamic Chunk Algorithm, to determine which frames are to be cached in the proxy server for the dynamic caching adjustment scenario. The algorithm guarantees the rate constraint over the server-proxy path to be satisfied for each level. This approach also maintains the set of cached frames at a higher level as a superset of the cached frames at a lower level. Hence, it enforces the proxy server to simply cache more data without dropping frames when it intends to reduce network bandwidth consumption for a video and vice versa.