电子信息专业英语复习

1 .3 Star P4

The star topology developed during the era when mainframes centrally controlled most computer communications. The voice switching world also employs a star topology when multiple remote switching nodes, each serving hundreds to even thousands of telephone subscribers, home-in on a large central switch. This network radiates in a star-like fashion from the central switch through the remote switches to user devices. The central node performs the communication switching and multiplexing functions in the star topology. Nodes communicate with each other through point-to-point or multipoint links radiating from the central node. The difference between this topology and the multipoint topology is that the central node only provides point-to-point connections between any edge nodes, on either a physical or logically switched basis.

星型拓扑结构发育在大型机集中控制大多数计算机通信的时代。语音切换领域在多个远程开关节时点也采用星型拓扑结构，每个服务于数百甚至数千名电话订阅者，安放在大型的中央交换机上。这个网络像星型一辐射，这个网络从中央交换节点通过远程交换到达用户设备。中央节点在星型拓扑结构中执行通信交换和多路复用功能。节点之间的连接，从中央节点通过点对点或多点链接辐射。这种拓扑结构和多点拓扑之间的区别是，中心节点只提供任在物理或逻辑上交换的基上的何边缘节点的点对点连接。

Figure 1 .5 shows a star topology, where Node A serves as the center of the star and Node B through E communicate via connections switched to and through the central Node A. An example of a star topology is many remote terminal locations, or clients, accessing a centralized server through the central node as illustrated in the figure. The physical star topology is widely used to connect devices to a central hub in LANs, and thus is often called a “hub and spoke” topology. The central hub may logically organize the physical star as a logical bus or ring as is commonly done in LAN wiring hubs. A key benefit of the physical star topology is superior network management of the physical interfaces. For example, if a single interface fails in a physical star topology, then the management system can readily disable it without affecting any other stations. Conversely, in a broadcast topology, a single defective switch can take down the entire shared medium network. As we shall see, many wide area networks also have a star topology, driven basically by the client-server computing paradigm.

图 1.5 显示星型拓扑结构，在节点A 作为星的中心而节点B 至 E 沟通通过连接切换到达和通过中央节点a。星型拓扑结构的一个例子是很多远程终端的地址或客户端，通过中心节点访问集中的服务器，如图所述。物理星型拓扑结构被广泛用于将设备连接到局域网的中央枢纽，因而通常被称为"中心和分支"的拓扑结构。中央集线器逻辑上可能把物理星型看成是一个逻辑总线或逻辑环，就好像局域网布线集线器一样。物理星型拓扑结构的关键好处是高级网络管理的物理接口。例如，如果在物理星型拓扑结构一个单一的接口没有成功，管理系统可以随时禁用它而不会影响任何其他接口的状态。相反，在广播的拓扑中，一个单一的缺陷开关可以取下整个共享介质网络。我们将会看到，很多的广域网络也有星型拓扑结构，基本上由客户端-服务器计算范式。

2 .

3 .1 Asynchronous and Synchronous Data Transmission P11

异步和同步数据传输

Asynchronous character transmission has no clock either in or associated with the transmitted digital data stream. Instead of a clock signal, start and stop bits delimit characters transmitted as a series of bits numbered 1 through 8 as illustrated in the example of Figure 2 .4 . There may be a variable amount of time bet ween characters. Analog modem communication