Section A Networking 网络

The need to share information and resources among different computers has led to linked computer systems, called networks, in which computers are connected so that data can be transferred from machine to machine.

不同计算机之间共享信息和资源的需求导致了计算机系统的互联，称为网络，其中计算机被连接起来，以便数据可以从一台机器传输到另一台机器。

1.Network Classifications网络分类

词汇

network - 网络

LAN (Local Area Network) - 局域网

MAN (Metropolitan Area Network) - 城域网

WAN (Wide Area Network) - 广域网

PAN (Personal Area Network) - 个域网

cable radio - 无线电

infrared - 红外线

open network - 开放网络

proprietary - 专有的

topology - 拓扑学

bus - 总线

Ethernet - 以太网

mesh - 网状；网格

hybrid - 混合的

open network - 开放网络

closed network - 封闭网络

public network - 公共网络

private network - 私有网络

proprietary network - 专有网络

bus network - 总线网络

ring network - 环形网络

star network - 星型网络

mesh network - 网状网络

tree network - 树形网络

A LAN normally consists of a collection of computers in a single building or building complex. For example, the computers on a university campus or those in a manufacturing plant might be connected by a LAN.

局域网通常由一栋建筑或建筑群中的计算机组成。例如，大学校园或制造厂内的计算机可能通过局域网连接。

A MAN is a network of intermediate size, such as one spanning a local community. 城域网是一种中等规模的网络，比如覆盖一个本地社区。

A WAN links machines over a greater distance — perhaps in neighboring cities or on opposite sides of the world. 广域网连接更远距离的机器——也许在邻近城市或世界对面。

Another means of classifying networks is based on whether the network’s internal operation is based on designs that are in the public domain or on innovations owned and controlled by a particular entity such as an individual or a corporation. 另一种分类网络的方法是基于网络的内部操作是基于公共领域的设计，还是基于由个人或公司等特定实体拥有和控制的创新。

Still another way of classifying networks is based on the topology of the network (Figure 6A-1), which refers to the pattern in which the machines are connected. 另一种分类网络的方法是基于网络的拓扑结构（图6A-1），这指的是机器连接的模式。

Two of the more popular topologies are the bus, in which the machines are all connected to a common communication line called a bus, and the star, in which one machine serves as a central focal point to which all the others are connected.
两种较流行的拓扑结构是总线，其中所有机器都连接到称为总线的公共通信线上；以及星型，其中一台机器作为所有其他机器连接的中心焦点。

Star networks are one of the most common computer network topologies. In its simplest form, a star network consists of one central node, typically a switch or hub, which acts as a conduit to transmit messages. 星型网络是最常见的计算机网络拓扑之一。在其最简单的形式中，星型网络由一个中心节点组成，通常是一个交换机或集线器，它作为传输消息的通道。

2.Combining Networks 组合网络

词汇

repeater - 中继器

bridge - 网桥

switch - 交换机

subtle        a微妙的

informative         a信息量大的

amplification - 放大

message - 报文

forward - 转发

autonomous - 自主的

router - 路由器

gateway        n网关

Sometimes it is necessary to connect existing networks to form an extended communication system. 有时需要连接现有网络以形成一个扩展的通信系统。

In the case of bus networks based on the Ethernet protocols, it is often possible to connect the buses to form a single long bus. This is done by means of different devices known as repeaters, bridges, and switches. 在基于以太网协议的总线网络的情况下，通常可以将总线连接起来形成一个长总线。这是通过使用称为中继器、网桥和交换机的不同设备来完成的。

Repeater: The simplest of these is the repeater, which is little more than a device that simply passes signals back and forth between the two original buses (usually with some form of amplification) without considering the meaning of the signals. 中继器：这些设备中最简单的是中继器，它只不过是一个在两个原始总线之间简单地来回传递信号的设备（通常带有一定的放大），而不考虑信号的含义。

Bridge: It looks at the destination address that accompanies each message and forwards a message across the connection only when that message is destined for a computer on the other side. 网桥：它查看每个消息附带的目的地址，并且只有在该消息注定要发送到另一边的计算机时，才将消息转发到连接上。

Sometimes, however, the networks to be connected have incompatible characteristics. For instance, the characteristics of a Wi-Fi network are not readily compatible with an Ethernet network. 然而，有时待连接的网络具有不兼容的特性。例如，Wi-Fi网络的特性与以太网不完全兼容。

The connection between networks to form an internet is handled by devices known as routers, which are special purpose computers used for forwarding messages. 形成互联网的网络连接由称为路由器的设备处理，路由器是用于转发消息的专用计算机。

Two Wi-Fi star networks and an Ethernet bus network connected by routers. 两个Wi-Fi星型网络和一个以太网总线网络通过路由器连接。

It first sends the message to the AP in its network. The AP sends the message to its associated router, and this router forwards the message to the router at the Ethernet. There the message is given to a machine on the bus, and that machine then forwards the message to its final destination in the Ethernet. 它首先将消息发送到其网络中的接入点（AP）。AP将消息发送到其关联的路由器，然后这个路由器将消息转发到以太网上的路由器。在那里，消息被传递给总线上的一台机器，然后这台机器将消息转发到以太网上的最终目的地。

The point at which one network is linked to an internet is often called a gateway because it serves as a passageway between the network and the outside world. 将一个网络连接到互联网的点通常被称为网关，因为它作为网络和外部世界之间的通道。

Gateways can be found in a variety of forms, and thus the term is used rather loosely. 网关可以有多种形式，因此这个术语的使用相当宽松。

In many cases a network’s gateway is merely the router through which it communicates with the rest of the internet. In other cases the term gateway may be used to refer to more than just a router. 在许多情况下，网络的网关只是它与互联网其余部分通信的路由器。在其他情况下，术语网关可能用来指不仅仅是路由器。

For example, in most residential Wi-Fi networks that are connected to the Internet, the term gateway refers collectively to both the network’s AP and the router connected to the AP because these two devices are normally packaged in a single unit. 例如，在大多数连接到互联网的住宅Wi-Fi网络中，术语网关统称为网络的接入点（AP）和连接到AP的路由器，因为这两个设备通常被包装在一个单元中。

3.Methods of Process Communication 进程通信方法

词汇

interprocess - 进程间

client/server - 客户/服务器

peer-to-peer - 对等网；点对点

swarm - 聚合；群

Methods of Process Communication

进程通信方法

network protocols - 网络协议

carrier sense multiple access with collision detection (CSMA/CD) - 载波侦听多路访问/碰撞检测 client/server model - 客户/服务器模型

peer-to-peer model - 对等网模型

client/server (C/S) - 客户/服务器 (C/S)

browser/server (B/S) - 浏览器/服务器 (B/S)

peer-to-peer (P2P) - 对等网 (P2P)

The various activities (or processes) executing on the different computers within a network (or even executing on the same machine via time-sharing/multitasking) must often communicate with each other to coordinate their actions and to perform their designated tasks.

在网络中不同计算机上执行的各种活动（或进程）（甚至通过时间共享/多任务在同一台机器上执行）通常必须相互通信，以协调它们的行动并执行它们指定的任务。

（1）client/server model - 客户/服务器模型

A popular convention used for interprocess communication is the client/server model. 用于进程间通信的流行约定是客户/服务器模型。

This model defines the basic roles played by the processes as either a client, which makes requests of other processes, or a server, which satisfies the requests made by clients. 该模型定义了进程扮演的基本角色，要么是客户端，它向其他进程提出请求，要么是服务器，它满足客户端提出的请求。

Today the client/server model is used extensively in network applications. 今天，客户/服务器模型在网络应用中得到了广泛使用。

（2）peer-to-peer (P2P) - 对等网（P2P）

The peer-to-peer model involves processes that provide service to and receive service from each other. 对等网模型涉及相互提供服务和相互接受服务的进程。

Moreover, whereas a server must execute continuously so that it is prepared to serve its clients at any time, the peer-to-peer model usually involves processes that execute on a temporary basis. 此外，虽然服务器必须持续运行，以便随时准备为其客户端服务，但对等网模型通常涉及临时执行的进程。

For example, applications of the peer-to-peer model include instant messaging in which people carry on a written conversation over the Internet as well as situations in which people play competitive interactive games. 例如，对等网模型的应用包括即时消息传递，人们可以在互联网上进行书面交谈，以及人们进行竞争性互动游戏的情况。

The peer-to-peer model is also a popular means of distributing files such as music recordings and motion pictures via the Internet. In this case, one peer may receive a file from another and then provide that file to other peers. 对等网模型也是通过互联网分发文件（如音乐录音和电影）的流行方式。在这种情况下，一个对等方可能从另一个对等方接收文件，然后向其他对等方提供该文件。

The collection of peers participating in such a distribution is sometimes called a swarm. The swarm approach to file distribution is in contrast to earlier approaches that applied the client/server model by establishing a central distribution center (the server) from which clients downloaded files. 参与这种分发的对等方集合有时被称为群。与早期采用客户/服务器模型通过建立中央分发中心（服务器）供客户端下载文件的方法相比，群的文件分发方法与之不同。

练习A1（知识点填空）

1. The need to share information and resources among different computers has led to linked computer systems, called networks, in which computers are connected so that data can be transferred from machine to machine.
   不同计算机之间共享信息和资源的需求导致了计算机系统的互联，称之为网络，其中计算机被连接起来，以便数据可以从一台机器传输到另一台机器。

2. A computer network is often classified as being either a LAN, a MAN, a WAN, or a PAN.
   计算机网络通常被分类为局域网(LAN)、城域网(MAN)、广域网(WAN)或个域网(PAN)。

3. The Internet is an open system, which is governed by an open collection of protocol suite. It operates on numerous methods and standards known as the TCP/IP protocol suite.
   互联网是一个开放的系统，由一套开放的协议集合管理。它运行在许多方法和标准上，被称为TCP/IP协议套件。

4. Based on the topology of the network, two of the more popular topologies are the bus and the star.
   根据网络的拓扑结构，两种较流行的拓扑是总线和星型。

5. A switch is essentially a bridge with multiple connections, allowing it to connect several buses rather than just two.
   交换机本质上是一个具有多个连接的桥梁，允许它连接多个总线而不仅仅是两个。

6. The connection between networks to form an internet is handled by devices known as routers.
   形成互联网的网络连接由被称为路由器的设备处理。

7. The point at which one network is linked to an internet is often called a gateway because it serves as a passageway between the network and the outside world.
   将一个网络连接到互联网的点通常被称为网关，因为它作为网络和外部世界之间的通道。

8. In most residential Wi-Fi networks that are connected to the Internet, the term gateway refers collectively to both the network's AP(access point ) and the router connected to the AP because these two devices are normally packaged in a single unit.
   在大多数连接到互联网的住宅Wi-Fi网络中，术语网关通常指网络的接入点(AP)和连接到AP的路由器，因为这两个设备通常被包装在一个单元中。

9. The popular convention used for interprocess communication is the client/server（C/S） model and the peer-to-peer (P2P) model.
   用于进程间通信的流行约定是客户/服务器模型和对等网(P2P)模型。

练习A2（词汇翻译）

• LAN (Local Area Network) - 局域网
• MAN (Metropolitan Area Network) - 城域网
• WAN (Wide Area Network) - 广域网
• PAN (Personal Area Network) - 个人区域网
• cable radio - 无线电
• open network - 开放式网络
• proprietary network - 专有网络
• bus topology - 总线拓扑
• Ethernet network - 以太网
• ring topology - 环形拓扑
• tree topology - 树形拓扑
• mesh topology - 网状拓扑
• hybrid topology - 混合拓扑
• repeater - 中继器
• bridge - 网桥
• switch - 交换机
• router - 路由器
• WiFi - 无线网络；无线上网；无线局域网
• AP (Access Point) - 接入点
• gateway - 网关
• client/server (C/S) - 客户/服务器模型
• peer-to-peer (P2P) - 对等网络模型

Section B distributed system 分布式系统

词汇

multifaceted        a多方面的

disturbed        a分布式的

middleware        n中间件

concurrency        n并发性

tolerance        n容忍

transparency        n透明性

heterogeneity        n异构性

inherit        a固有的，内在的

cluster        n集群

throughout        n吞吐量

grid         n网络

volunteer        v自愿去做

voluntary        n自愿；a自愿的

dynamically        adv动态的

练习B1（知识点填空）

1. A distributed system consists of a collection of autonomous computers, connected through a network and distribution middleware.
   分布式系统由一组自治计算机组成，通过网络和分布式中间件相连接。

2. Middleware is a class of software technologies designed to help manage complexity and heterogeneity inherent in distributed systems.
   中间件是一类软件技术，旨在帮助管理分布式系统中固有的复杂性和异构性。

3. Cluster computing is a type of parallel or distributed processing system, which consists of a collection of interconnected stand-alone computers cooperatively working together as a single, integrated computing resource.
   集群计算是一种并行或分布式处理系统，它由一组相互连接的独立计算机组成，这些计算机作为单一的集成计算资源协同工作。

4. Grid computing aims to "enable resource and coordinated problem solving in dynamic, multi-institutional virtual organizations".
   网格计算旨在“在动态的、多机构的虚拟组织中“实现资源和协调问题的解决”。

5. Cloud computing is hinting at a future in which we won't compute on local computers, but on centralized facilities operated by third-party compute and storage utilities.
   云计算暗示着未来我们不会在本地计算机上进行计算，而是在由第三方计算和存储工具运行的集中设施上进行计算。

练习B2（词汇翻译）

• information retrieval - 信息检索
• distributed system - 分布式系统
• fault tolerance - 容错性
• cluster computing - 集群计算
• load-balancing - 负载均衡
• grid computing - 网格计算
• cloud computing - 云计算