计算机局域网的维护

介绍了计算机局域网的基本知识，具体分析了计算机局域网的硬件设备和网络协议的使用环境，详细介绍了交换机与集线器之间的不同之处、组建计算机局域网时如何正确选用网络协议。在总结个人工作经验的基础上，详细介绍了网络维护时常见的几个软件工具的使用方法。     

Medium access control protocol for the integration of voice/data on a local area network

The analysis and performance of an integrated medium access protocol based on R-VT-CSMA for packet voice and data transmission on a broadcast-bus LAN is examined. This protocol, called adaptive R-VT-CSMA uses variable length packets and the strong correlation between successive voice frames to increase the throughput.<>     

Packet communication protocol for image services on a high-speedmultimedia LAN

The authors describe the requirements for high-speed multimedia communication and propose a high-speed communication protocol to provide congestion-free access and efficient retransmission/flow control. Its usefulness is proved in a 400 Mb/s multiaccess loop local area network (LAN) with a 100 Mb/s user interface. The main characteristics of the protocol are separation of image communication handling, guarantee of no buffer overflow in a network, and end-to-end block-based transfer. Buffer reservation control in the user-network interface and a retransmission scheme based on a long-size block are used to realize high-speed congestion control and error recovery. A multimedia terminal architecture suitable for real-time image communication is also discussed. In the prototype system, a few frames of high-resolution image information can be transferred in a second. Around 26 Mb/s effective throughput between application entities has been obtained     

The CSMA/DM LAN protocol

We propose an extension of the classical CSMA/CD protocol that eliminates its three main drawbacks. The new protocol, called dual‐mode CSMA/CD (CSMA/DM), operates in two modes, light mode and heavy mode. The light mode of CSMA/DM is almost the same as the original CSMA/CD protocol and is primarily used when the LAN load is light. The heavy mode is a collision free mode and is applied when the LAN load is heavy. The proposed modification to CSMA/CD is minimal while performance gain is significant. CSMA/DM automatically switches between its two modes based on the observed LAN load. Under heavy mode, the monitor station in a CSMA/DM LAN allocates bandwidth to those busy stations without collisions. The newly added priority scheme in the heavy mode allows stations to reserve bandwidth for their high priority frames. Compared with the current collision‐free fast Ethernet and Gigabit Ethernet, CSMA/DM has the advantage of not needing any extra switches or hubs while maintaining comparable performance. Its priority scheme provides more flexibility on bandwidth distribution than in fast Ethernet and Gigabit Ethernet. It can also be easily adapted for high‐speed wireless LANs. More importantly, CSMA/DM should be a good alternative of the widely used CSMA/CA (collision avoidance) in mobile ad hoc networks (MANET) and sensor networks. Copyright © 2005 John Wiley & Sons, Ltd.     

Idle-signal casting multiple access with collision resolution(ICMA/CR) protocol for wireless LAN

The authors propose an idle-signal casting multiple access with collision resolution (ICMA/CR) protocol for wireless LAN. This protocol focuses on efficient collision resolution by adopting the binary-tree protocol. By using the collision resolution algorithm, the retransmission process can be controlled so that collisions are resolved more efficiently using nearly immediate feedback information, thereby increasing the throughput-delay performance of the ICMA/CD protocol     

Batch Throughput Efficiency of ADCCP/HDLC/SDLC Selective Reject Protocols

The batch throughput efficiency is studied for three variants on selective reject protocols that operate in a full duplex asynchronous response mode and that adhere to the common architectural features of ADCCP, HDLC, and SDLC. In these architectures, the receiver of information frames may use the REJ supervisory frame to request the sender of information frames to back up to an earlier point in the send sequence. Alternatively, the receiver of information frames may issue the SREJ supervisory frame, which requests resending of a single previous information frame followed by continuation of the ongoing send sequence. The first protocol discussed here uses SREJ as the principle method for recovering lost frames but reverts to REJ recovery if certain combinations of errors occur. The second protocol uses SREJ as the only means for recovery. The third protocol uses SREJ for "isolated" frame losses; if a second frame loss occurs within a specified time after the first, then recovery of the first loss is done by REJ. Results plotted for transmission via satellite at 1.544 Mbits/s show that the selective reject protocols permitted by the current versions of ADCCP, HDLC, and SDLC outperform the simpler REJ protocol only for bit error rates in a narrow range. Thus, it may be worthwhile to consider modifications to these architectures that will permit more flexible selective reject protocols.     

适配于ISDN的综合业务局域网设计

现有ＬＡＮ的传输能力在很大程度上可满足传输综合业务的要求，现有ＬＡＮ适配于ＩＳＤＮ的直接方法是在ＬＡＮ上实现ＩＳＤＮ功能，从而达到ＬＡＮ工作站与ＩＳＤＮ间业务的完全互通，在ＬＡＮ上实现ＩＳＤＮ功能的方案是：（１）在ＬＡＮ上增加综合业务传输接口，该接口不同于ＬＡＮ软件提供的接口，具有实时性，而且该接口的设计应使ＬＡＮ应用与综合业务应用间互相独立；（２）开发在工作站上与ＬＡＮ应用软件并发运行的综合业务     

Handover management for mobile nodes in IPv6 networks

We analyze IPv6 handover over wireless LAN. Mobile IPv6 is designed to manage mobile nodes' movements between wireless IPv6 networks. Nevertheless, the active communications of a mobile node are interrupted until the handover completes. Therefore, several extensions to Mobile IPv6 have been proposed to reduce the handover latency and the number of lost packets. We describe two of them, hierarchical Mobile IPv6, which manages local movements into a domain, and fast handover protocol, which allows the use of layer 2 triggers to anticipate the handover. We expose the specific handover algorithms proposed by all these methods. We also evaluate the handover latency over IEEE 802.11b wireless LAN. We compare the layer 2 and layer 3 handover latency in the Mobile IPv6 case in order to show the saving of time expected by using anticipation. We conclude by showing how to adapt the IEEE 802.11b control frames to set up such anticipation.     

综合业务城域网IEEE802.5预约级协议改进策略

预约是局域网(LAN)中常见的存取方式,尤其以环形LAN的IEEE802.5预约级协议著称。为了在综合业务的环形城域网(MAN)中利用预约级协议,必须考虑综合业务的特点,对IEEE802.5预约级协议进行改进。其出发点是既要尽可能保证高优先级信息能提前预约,又要防止出现低优先级信息(特别是最低优先级信息)长时间得不到发送的局面。该文提出的高预约级中断策略,比较合理地解决了这一问题。其实质是在合理范围内牺牲高优先级业务的服务质量,换来部分提高低优先级业务的服务质量。模拟实验表明,改进后的IEEE802.5预约级策略适合于综合业务MAN的利用。     

Performance Evaluation of Multireject, Selective Reject, and Other Protocol Enhancements

This study compared the effects on performance of four features of the LAPB and LAPD protocols. LAPB is the link level for the X.25 protocol, and LAPD is the link level for the ISDN "D" signaling channel. The features were: multireject in which additional reject or selective reject frames can be retransmitted under certain conditions, selective reject in which an entity can request selected frames to be retransmitted, the null information frame (NIF) with which additional control frames are sent to help detect missing frames, and multiple service access points (SAP's) in which several link-level protocol handlers are multiplexed on the same physical link (a feature unique to LAPD). Results indicate that the current standard LAPB/D protocol with multireject is the preferred protocol. Selective reject generally performed worse than the standard protocol, and offered improvement only with complex and expensive enhancements. The NIF feature yielded a virtually unnoticeable performance improvement. Multi-SAP introduced a virtually unnoticeable impairment when it was used to carry the same traffic load as a single SAP.     

Throughput behavior of link adaptive 802.11 DCF with MUD capable access node

Conventional IEEE 802.11 medium access control (MAC) protocol discourages simultaneous transmission to avoid collisions. With fast advances in physical layer technologies, multi-user detection (MUD) capable receivers which can detect multiple frames from different users simultaneously become available. If we are to utilize them in today's wireless LAN, however, it is not entirely clear how we should change the MAC and how much benefit is available and can be obtained by doing so. The primary objective of this paper is to investigate such questions. We approach this objective by developing a new throughput expression for 802.11 distributed coordination function (DCF). The derived expression has been verified in simulation. We show that significant throughput gain can be garnered with slight modification in 802.11 DCF.     

The OpenView Enterprise Management Framework

In OpenView, Hewlett-Packard has concentrated on creating a multivendor management platform for TCP/IP-based internets. This plays to the company's strengths in LAN management, where it has been a major player in the LAN protocol analyzer market since the early 1980s, and its expertise in TCP/IP, which the company had been using internally since the early 1980s.     

多媒体通信的吉比特HMR协议

本文介绍了一个ＨＭＲ（高速多媒体通信环网）协议。这个协议建立在吉比特的ＬＡＮ／ＭＡＮ（局域网／城域网）上，并以ＭＡＣ（媒体存取控制）协议和ＡＴＭ（异步转移模式）来传送信息。为了使最大的存取延迟和存储媒体带宽损失达到最小，ＨＭＲ协议采用多窗口标记算法，这种算法的每个优先级都有它自己的最好控制窗口标记。     

Hub‐polling‐based IEEE 802.11 PCF with integrated QoS differentiation

IEEE 802.11 is one of the most influential wireless LAN (WLAN) standards. Point coordination function (PCF) is its medium access control (MAC) protocol with real‐time traffic (rt‐traffic) quality‐of‐service (QoS) guarantees. In PCF, it is very likely that non‐real‐time traffic (nrt‐traffic) will use the contention free period (CFP) that should be dedicated to traffic having higher priority such as rt‐traffic. Therefore, a modified PCF protocol called MPCF, which is based on hub polling and an integrated QoS differentiation, is presented in this paper. With the integrated QoS differentiation, MPCF can prioritize bandwidth requests according to service classes and QoS requirements. With hub polling, MPCF can reduce the bandwidth for control frames and improve the network throughput. A simple and accurate analytical model is derived and presented in this paper to calculate the system throughput of MPCF. Simulation results show that MPCF protocol is much better than PCF in terms of system capacity and rt‐traffic QoS guarantees. Copyright © 2008 John Wiley & Sons, Ltd.     

基于Nios II的嵌入式Web服务器

21世纪计算机网络已经成为人们广泛使用的工具。通过计算机网络,人们可以进行网络控制、信息交换等。本文介绍一种基于NiosII处理器的嵌入式Web服务器的设计方法。系统在Cyclone系列1C20F400C7芯片上,采用软核处理器NiosII来配置核心处理器。NiosII核是用户可随时配置和构建的32位指令集和数据通道的嵌入式系统微处理器IP核,网络协议采用LWIP,这是一种专门针对嵌入式系统应用而设计的网络通信协议,接口芯片使用LAN9C111。本文基于NiosII的嵌入式Web服务器能够达到预期的效果,用户可以通过IE浏览器浏览存储在FLASH芯片中的网页,由于CPU本身是以软核的方式实现,其功能可根据需要进行定制,非常灵活。     

The Demand Priority MAC protocol

A new technology needs to offer more than just 100 Mb/s. To succeed in the LAN marketplace, a new LAN technology must be very cost competitive with the established LANs, such as Ethernet and Token Ring, while also providing backwards compatibility with existing network software. We describe a new 100-Mb/s LAN technology that has these characteristics This technology is being defined as an open standard within the IEEE Project 802.12 Demand Priority group. Two important objectives were established for this LAN technology: first, it should be able to use the unshielded twisted pair (UTP) wiring found in a large number of installations and, in particular, to use the same wiring as defined for use in 1OBase-T. This objective was later extended to encompass support for the shielded twisted pair (STP) used for IEEE 802.5. This will enable the majority of current LAN users to benefit from their enormous investment in cable plant. The second objective was that the network should support new applications, such as video conferencing and remote training, while also providing backwards compatibility with the massive installed software base. Both objectives have been met. The Demand Priority MAC protocol currently being standardized in IEEE 802.12, offers substantial benefits over the CSMA/CD protocol of IEEE 802.3. By preserving both the current wiring infrastructure and investment in software, and by using the very simple Demand Priority MAC protocol, 100 Mb/s LANs could soon be as low-cost as 10Base-T is today     

LXI设备多用户访问控制与数据共享方法

在分析现有局域网扩展仪器（LXI）设备的特点和实际使用情况的基础上,指出存在多用户访问控制冲突和数据共享的问题.通过采用重叠IO 加事件通知的方法来增加服务器端的承载能力,并利用VXI-11 协议实现互斥访问控制.利用Silverlight 支持用户数据包协议（UDP）的特点,将网络负载压力转移到程控端,实现数据共享.在不同测试环境中进行的测试结果显示,本文采用的方法能有效增加LXI 设备的网络负载,提高信息同步的能力以及设备安全性.     

Data communications using ATM: architectures, protocols, andresource management

The introduction of ATM is being propelled by the need for fast data communications in public and private networks. What is needed is a clear picture of protocol architectures and traffic characteristics of the various applications to be supported both now and in the future. The authors discuss ATM network architectures with special focus on the support of connectionless LAN interconnection and show which benefits can be obtained from the introduction of a connectionless server in an ATM network. They outline issues related to the use of existing protocols when ATM networks are introduced and show which protocol complexities have to be handled by gateways and servers, again using the example of connectionless LAN interconnection. Having presented network and protocol architectures the issue of data communication in ATM, resource allocation, is treated