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计算机网络

2017-4-29 00:38| 投稿: caiflyer |来自: 互联网

摘要: 计算机网络可用于多种服务,即为公司也为个人。对公司而言,由使用共享服务器的个人计算机组成的网络提供了灵活的方式和很好的价格/性价比。对个人而言,网络提供访问各种各样的信息和娱乐资源的接口。大致来说可以 ...

计算机网络可用于多种服务,即为公司也为个人。对公司而言,由使用共享服务器的个人计算机组成的网络提供了灵活的方式和很好的价格/性价比。对个人而言,网络提供访问各种各样的信息和娱乐资源的接口。

大致来说可以分为局域网、城域网、广域网、因特网,每一种网都有自己的特点、技术、速度、位置。局域网覆盖一栋建筑物,城域网覆盖一座城市,广域网覆盖一个国家或大陆。局域网和城域网是非交换网络(也就是没有路由器),广域网是交换网络。

网络软件由协议和通信过程的规则组成。协议既可以是无连接的也可以是面向连接的。大部分的网络支持分层协议,每一层为它的下层服务。典型的协议栈不是基于IOS就是TCP/IP模式。这两种模式都有网络层、传输层和应用层,但其它层有所不同。

1-局域网

LAN是英文Local Area Network的首字母缩写,是指分散在一个较大的有限区域内的,由通信线路连接起来的计算机和设备,在该网络上的任何设备能与网络上的其它设备相互作用。局域网一般包括微型机和共享资源(通常价格昂贵),如激光打印机和大硬盘。大多数局域网络能支持各种计算机和设备。对一定的局域网络,每一种设备必须使用物理和数据连接协议,而且所有要在该网络上相互通信的装置都必须使用相同的上层通信协议。虽然单一的局域网络受到地理限制,但是,单独的局域网络仍能被连接成大网络。类似的局域网由网桥加以连接,网桥是网络之间的传输点。不同类型的局域网由网关加以连接。网关既可以传输数据,又可以根据接收网络使用的协议进行转换。

局域网上的设备被视为节点,节点由传输信息的电缆连接。电缆类型包括双绞线、同轴电缆、光纤。局域网上节点可按三种基本拓扑结构的任何一种连接,即总线型、环形、星形。

为了避免潜在的冲突,当两个或者更多的节点试图同时传输的时候,局域网利用争用和冲突检测或者令牌传递来调节通道。

2-以太网络

以太网是在1976年由施乐公司发展起来的局域网络,最初用来连接在Palo Auto研究中心的小型机。以太网是一个被广泛采用的网络,争用网络的IEEE802.3标准即由此发展起来的。以太网使用总线拓扑结构配置,并且依靠所谓的CSMA/CD访问方式来调节主通信线路上的交通。网络节点由同轴电缆或者是双绞线以粗细两种方式任意连接。细以太网电缆直径为5mm,能在300m范围内连接网络站;粗以太网电缆直径为1cm,能在相距1000m

范围内连接网络站。以太网以不同长度的帧传递信息,每帧除了包含传输与控制信息外,还可携带长达1500B的资料信息。最初以太网的基带传输标准是10Mb/s。

3-总线网络

在科学计算中,总线网络属于局域网的拓扑结构配置,其中所有节点均被连接一主通信线路(总线)上。在总线网络上,每一个节点都监控线路上的活动,所有节点都能检测到信息,但只有地址节点才能接收信息。因为总线网络依赖于公共信息公路,因此一个故障节点就可使它通信中断。为了避免发生冲突,当线路上两个或者多个节点试图同时利用总线时,网络一般依赖于冲突检测或令牌传递来调节通道。

4-星形网络

星形网络是局域网,其中每一个设备都连着一台中央计算机,该中央计算机以星形结构配置拓扑。一般情况下,网络是由一台中央计算机及其周围终端组成。在星形网络中,信息从节点传到中央计算机,中央计算机再做必要的进一步传递处理。星形网络某节点故障不会影响网络上其它节点,但中央计算机故障会导致整个网络中断。

5-环形网络

环形网络是局域网,其中设备(节点)按闭合回路或圆环方式连接。环形网络中的信息沿一个方向传递,从一个节点传到另一个节点。因为信息绕环传递,故每一个节点可检查信息所属的终点位置。如果地址与节点所配信息一样,则节点接受该信息;否则,它会重新生成该信息,并且将信息沿着环传到下一节点。这样使得环形网络比星形网络覆盖面积大。也可进行设计让信息通过任何故障或者出错节点。然而,由于是闭合回路,增加新的节点会比较困难。

本文摘自《计算机英语》,图片均来自网络。

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