局域網(wǎng)外文翻譯(一)

1、外 文 翻 譯論文題目：大型企業(yè)網(wǎng)絡(luò)的設(shè)計(jì)與規(guī)劃姓名：賈龍飛學(xué)號(hào)：201120210230班級(jí)：1122102班年級(jí)：2011級(jí)專業(yè)：網(wǎng)絡(luò)工程學(xué)院：軟件學(xué)院指導(dǎo)教師：王志波（講師）完成時(shí)間：二一五 年 四 月目錄1.COMPUTER NETWORKS2DATE COMMUNICATIONS22.ARCHITECTURE OF COMPUTER NETWORKS31.The OSI Reference Model32.The TCP/IP Reference Model33.WIDE AREA NETWORK41.CIRCUIT SWITCHED NETWORKS42LEASED LINE NE

2、TWORKS53.PACKET SWITCHING NETWORKS54.LOCAL AREA NETWORK61.Topology62.Transmission media63. Medium access control methods61.計(jì)算機(jī)網(wǎng)絡(luò)7數(shù)據(jù)通信72.計(jì)算機(jī)網(wǎng)絡(luò)的體系結(jié)構(gòu)81.OSI參考模型82.TCP/IP參考模型83.廣域網(wǎng)91.電路交換網(wǎng)92.專線網(wǎng)93.分組交換網(wǎng)94.局域網(wǎng)101.拓?fù)浣Y(jié)構(gòu)102.傳輸媒體113.媒體訪問控制方法111.COMPUTER NETWORKS DATE COMMUNICATIONSThe end equipment which eith

3、er generates the digital information for transmission or uses the received digital data can be computer ,printers ,keyboards, CRTs, and so on. This equipment generally manipulates digital information internally in word unitsall the bits that make up a word in a particular piece of equipment are tran

4、sferred in parallel. Digital data, when transmitted, are in serial form. Parallel transmission of an 8-bit word require eight pairs of transmission linesnot at all cost-effective. Data terminal (DTE) is a general phrase encompassing all of the circuitry necessary to perform parallel-to-serial and se

5、rial-to-parallel conversions for transmission and reception respectively and for data link management. The UART (Universal Asynchronous Receiver/Transmitter) and USART (Universal Asynchronous/Asynchronous Receiver/Transmitter) are the devices that perform the parallel-to-serial and serial-to-paralle

6、l conversions. The primary DTE includes a line control unit (LCU or LinCo) which controls the flow of information in a multipoint data link system. A station controller (STACO) is the corresponding that belonged to the subscriber in a data link system. Between the DTEs, starting with the modems, was

7、 communications equipment owned and maintained by Telco property.Data communications equipment (DCE) accepts the serial data stream from the DTE and converts it to some form of analog signal suitable for transmission on voice-grade lined. At the receive end, the DCE performs the reverse function of

8、converting the received analog signal to a serial digital data stream. The simplest form of DCE is a modem (modulator/demodulator) or data set. At the transmit end, the modem can be considered a form of digital-to-analog converter, while at the receive end, it can considered a form of analog-to-digi

9、tal converter. The most common of modulation by modems are frequency shift keying (FSK), phase shift keying (PSK), and quadrature amplitude modulation (QAM). This is a typically data transmission mode using the analog telephone lines. If you transmit data by digital channel (sometimes it is called “

10、Digital T-carrier”), a pulse Code Modulation (PCM) equipment must be used. A microwave transmission system can also be used for the data communication. Finally, you can use the satellite communication system for data transmission.If the cables and signal levels used to interconnect the DTE and DCE w

11、ere left unregulated, the variations generated would probably be proportional to the number of manufacturers. Electronics industries Association (EIA),an organization of manufactures with establishing the DTE and modem. This is a 25-pincable whose pins have designated functions and specified signal

12、levels. The RS-232C is anticipated to be replaced by an update standard.2.ARCHITECTURE OF COMPUTER NETWORKSComputer network is a complex consisting of two or more conned computing units, it is used for the purpose of data communication and resource resource sharing. Design of a network and its logic

13、al structure should comply with a set of design principles, including the organization of functions and the description of data formats and procedure. This is the network architecture and so called as a set of layers and protocols, because the architecture is a layer-based.In the next two sections w

14、e will discuss two important network architectures, the OSI reference model and the TCP/IP reference model.1.The OSI Reference ModelThe OSI model is shown in Fig.14-2(minus the physical medium). This model is based on a proposal developed by the International Standards Organizations (OSI) as the fir

15、st step toward international standardization of the protocols used in the various layers. The model is called the ISO OSI (Open System Interconnection) Reference Model because it deals with connecting open systems-that is, systems that are open for communication with other systems, We will usually j

16、ust call it the OSI model for short.The OSI model has seven has seven layers. Note that the OSI model itself is not a network architecture because it does not specify the exact services and protocols to be used in each layer. It just tells what each layer should do. However , However, ISO has also p

17、roduced standards for all the layers, although these are not part of the reference model itself. Each one has been published as a separate international standard.2.The TCP/IP Reference Model The TCP/IP reference model is an early transport protocol which was designed by the US Department of Defence

18、(DOD) around in 1978. It is often claimed that it gave rise the OSI “connectionless” mode of operation. TCP/IP is still used extensively and is called as a industrial standard of internet work in fact, TCP/IP has two parts: TCP and IP. TCP means it is on the transport layer and IP means it is on the

19、 network layer separately.1.There are two end-to-end protocols in the transport layer, one of which is TCP (Transmission Control Protocol) , another is UDP (User Datagram Protocol). TCP is a connection-oriented protocol that allows a byte stream originating on one machine to be delivered without err

20、or on any other machine in the internet. UDP is an unreliable, connectionless protocol for application that do not want TCPs sequencing of flows control flow control and wish to provide their own.2.The network layer defines an official packet format and protocol called IP (Internet protocol). The jo

21、b of the network layer is to deliver IP packets where they are supposed to go.The TCP/IP Reference Model is shown in Fig.14.3. On top of the transport layer is the application layer, It contains all the higher-level protocols. The early ones included virtual terminal (TELNET), file transfer (FTP), e

22、lectronic mail (SMTP) and domain name service(DNS). 3.WIDE AREA NETWORKA wide area network, or WAN, spans a large geographical area, often a country or continent . It contains a collection of machines intended for running user (i. e. , application) programs. We will follow traditional usage and call

23、 these machines hosts. By a communication subnet, or just subnet for short. The job of the subnet is to carry messages from host to host, just as the telephone system carries words from speaker to listener. By separating the pure communication aspects of the network (the subnet) from the application

24、 aspects (the hosts), the complete network design is greatly simplified. Relation between hosts and the subnet is shown in Fig.14-4.One of many methods that can be used to categorize wide area networks is with respect to the flow of information on a transmission facility. If we use this method to ca

25、tegorize wide area networks, we can group them into three basic types: circuit switched, leased line and packet switched.1.CIRCUIT SWITCHED NETWORKSThe most popular type of network and the one almost all readers use on a daily basis is a circuit switched network. The public switched telephone networ

26、k, however, is not limited to the telephone company, By purchasing appropriate switching equipment, any organization can construct their own internal circuit switched network and, if desired, provide one or more interfaces to the public switched network to allow voice and data transmission to flow b

27、etween the public network and their private internal network 2LEASED LINE NETWORKSThis is a dedicated network connected by leased lines. Leased line is a communications line reserved for the exclusive use of a leasing customer without inter-exchange switching arrangements. Leased or private lines ar

28、e dedicated to the user. This advantage is that the terminal or computer is a always physically connected to the line. Very short response times are met with service.3.PACKET SWITCHING NETWORKS A packet network is constructed through the use of equipment that assembles and disassembles packets, equi

29、pment that routes packet, and transmission facilities used to route packets from the originator to the destination device. Some types of data terminal equipment (DTE) can create their own packets, while other types of DTE require the conversion of their protocol into packets through the use of a pac

30、ket assembler / disassemble (PAD). Packets are routed through the network by packet switches. Packet switches examine the destination of packets as they flow through the network and transfer the packets onto trunks interconnecting switches based upon the packet destination destination and network ac

31、tivity. Many older pubic networks follow a standard called X.25. It was developed during 1970s by CCITT to provide an interface between public packet-switched network and their customers.CCITT Recommendation X.25 controls the access from a packet mode DTE, such as a terminal device or computer syste

32、m capable of forming packets, to the DCE at a packet mode. CCITT Recommendation X.28 controls the interface between non-packet mode devices that cannot interface between the PAD and the host computer. CCITT Recommendation X.3 specifies the parameter settings on the PAD and X.75 specifies the interfa

33、ce between packet network.4.LOCAL AREA NETWORK Local area data network , normally referred to simply as local area network or LANs, are used to interconnect distributed communities of computer-based DTEs located within a building or localized group of building. For example, a LAN may be used to inte

34、rconnect workstations distributed around offices within a single building or a group of buildings such as a university campus. Alternatively, it may be complex. Since all the equipment is located within a single establishment, however, LANs are normally installed and maintained by the organization.

35、Hence they are also referred to as private data networks. The main difference between a communication path established using a LAN and a connection made through a public data network is that a LAN normally offers much higher date transmission rates because of the relatively short physical separation

36、s involved. In the context of the ISO Reference Model for OSI, however, this difference manifests itself only at the lower network dependent layers. In many instances the higher protocol layers in the reference model are the same for both types of network. Before describing the structure and operati

37、on of the different types of LAN, it is perhaps helpful to first identify some of the selection issues that must be considered. It should be stressed that this is only a summary; there are also many possible links between the tips of the branches associated with the figure.1.Topology Most wide area

38、networks, such as the PSTN, use a mesh (sometimes referred to as a network) topology. With LANs, however, the limited physical separation of the subscriber DTEs allows simpler topologies to be used. The four topologies in common use are star, bus ,ring and hub.The most widespread topology for LANs d

39、esigned to function as data communication subnetworks for the interconnection of local computer-based equipment is the hub topology, which is a variation a variation of the bus and ring. Sometimes it is called hub/tree topology.2.Transmission mediaTwisted pair, coaxial cable and optical fiber are th

40、e three main type of transmission medium used for LANs.3. Medium access control methodsTwo techniques have been adopted for use of the medium access control in the LANs. They are carrier-sense-multiple-access with collision detection (CSMA/CD), for bus network topologies, and control token, for use

41、with either bus or ring networks.CSMA/CD is used to control multiple-access networks. Each on the network “l(fā)istens” before attempting to send a message, waiting for the “traffic” to clear. If two stations try to sent their messages at exactly the same time, a “collision” is detected, and both statio

42、ns are required to “step back” and try later.Control token is another way of controlling access to a shared transmission medium that is by the use of a control (permission) token. This token is passed form one DTE to another according to a defined set of rules understood and adhered to by all DTEs c

43、onnected to the medium. ADTE may only transmit a frame when it is in possession of the token and, after it has transmitted the frame, it passed the token on to allow another DTE to access the transmission medium.1計(jì)算機(jī)網(wǎng)絡(luò)數(shù)據(jù)通信端設(shè)備可以是計(jì)算機(jī)、打印機(jī)、鍵盤、CRT等，它們可以產(chǎn)生要發(fā)送的數(shù)字信息，也可使用所接收的數(shù)字?jǐn)?shù)據(jù)。這種設(shè)備通常在內(nèi)部以字為單位處理數(shù)字信息在一個(gè)實(shí)際設(shè)備中

44、構(gòu)成一個(gè)字的所有位是并行傳遞的。數(shù)字?jǐn)?shù)據(jù)在發(fā)送一個(gè)8對(duì)傳輸線，這是不經(jīng)濟(jì)的。那些在發(fā)送、接收數(shù)據(jù)分別完成并-串和串-并轉(zhuǎn)換并進(jìn)行數(shù)據(jù)鏈路管理的所有電路，一般稱為數(shù)據(jù)終端設(shè)備（DTE）。UART（通用異步接收/發(fā)送器）和USART（通用同步/異步接收/發(fā)送器）是實(shí)現(xiàn)并-串和串-并轉(zhuǎn)換的設(shè)備。主DTE包括控制多點(diǎn)數(shù)據(jù)鏈路系統(tǒng)中信息流的線路控制部件（LCU或LinCo）。從設(shè)備一方的相應(yīng)設(shè)備是工作站控制器（STACO）。如果DTE有與LCU相關(guān)的軟件，則稱為前端處理機(jī)（FEP）。同時(shí)，DTE也是數(shù)據(jù)鏈路系統(tǒng)中屬于用戶的最后一個(gè)設(shè)備。在兩個(gè)DTE之間，先是調(diào)制解調(diào)器，接著是屬于并有電話公司維護(hù)的通信設(shè)

45、備。最近的調(diào)整結(jié)果是調(diào)制解調(diào)器已不屬于電話公司獨(dú)家管理的設(shè)備了。數(shù)據(jù)通信設(shè)備（DCE）從DTE接收串行數(shù)據(jù)流，并將其轉(zhuǎn)化成適合在話音線路上發(fā)送的某種模擬信號(hào)形式。在接收端，DCE完成相反的功能，把接收到的模擬信號(hào)轉(zhuǎn)換成串行數(shù)字?jǐn)?shù)據(jù)流。最簡(jiǎn)單的DCE是調(diào)制解調(diào)器或數(shù)傳機(jī)。在發(fā)送端，調(diào)制解調(diào)器可以視為一種數(shù)/模轉(zhuǎn)換器，而在接收端則可視為一種模/數(shù)轉(zhuǎn)換器。調(diào)制解調(diào)器最常用的幾種調(diào)制方式是移頻鍵控（FSK）、移相鍵控（PSK）和正交調(diào)幅（QAM）。這是一種典型的使用模擬電話線路傳輸數(shù)據(jù)的方式。如果使用數(shù)字通信（有時(shí)稱為T-載波）傳輸數(shù)據(jù)，則必須使用脈碼調(diào)制（PCM）設(shè)備。也可以用微波傳輸系統(tǒng)進(jìn)行的數(shù)據(jù)

46、通信，當(dāng)然還可以用衛(wèi)星通信系統(tǒng)去傳輸數(shù)據(jù)。如果鏈接DTE和DCE的電纜和信號(hào)電平都是未調(diào)整的，則所產(chǎn)生的偏差就是可能與生產(chǎn)廠家的數(shù)量成正比。電子工業(yè)協(xié)會(huì)（EIA）（由關(guān)心建立行業(yè)標(biāo)準(zhǔn)的廠家組成的組織）同意將RS-232C作為DTE和調(diào)制解調(diào)器間的標(biāo)準(zhǔn)接口。它是一個(gè)25針電纜，每一針都規(guī)定了功能及信號(hào)電平，預(yù)計(jì)RS-232C將被修訂的標(biāo)準(zhǔn)所取代。2計(jì)算機(jī)網(wǎng)絡(luò)的體系結(jié)構(gòu)計(jì)算機(jī)網(wǎng)絡(luò)是由兩個(gè)或多個(gè)計(jì)算機(jī)設(shè)備互連而成的一種復(fù)合系統(tǒng)，用于數(shù)據(jù)通信和資源共享。網(wǎng)絡(luò)設(shè)計(jì)及邏輯結(jié)構(gòu)應(yīng)該遵循一套設(shè)計(jì)原則，包括功能的組織與數(shù)據(jù)格式和過程的描述，這就是網(wǎng)絡(luò)的體系結(jié)構(gòu)。由于這種體系結(jié)構(gòu)是分層次的，故又稱為一組層次和協(xié)議

47、。下面兩節(jié)將討論兩個(gè)重要的網(wǎng)絡(luò)體系結(jié)構(gòu)，即OSI參考模型和TCP/IP參考模型。1OSI參考模型OSI模型如圖14-2所示（物理介質(zhì)未畫出）。這一模型是基于國際標(biāo)準(zhǔn)化組織（ISO）提出的一個(gè)建議，作為用于各層次的國際標(biāo)準(zhǔn)協(xié)議的第一步。該模型也稱為ISO開放系統(tǒng)互連參考模型，因?yàn)樗婕伴_放系統(tǒng)的互連，即于其他系統(tǒng)的通信是開放的，通常簡(jiǎn)稱為OSI模型。OSI模型有7層。應(yīng)該注意的是，OSI模型本身并不是一種網(wǎng)絡(luò)體系結(jié)構(gòu)，因?yàn)樗痪唧w規(guī)定每一層所使用的確切的服務(wù)和協(xié)議。它只是說明每一層應(yīng)該做什么。然而，ISO還是對(duì)各層制定出了標(biāo)準(zhǔn)，盡管這些標(biāo)準(zhǔn)不是參考模型本身的一部分。每一層都作為一個(gè)單獨(dú)的國際標(biāo)準(zhǔn)

48、來頒布。2TCP/IP參考模型TCP/IP參考模型是美國國防部大約于1978年設(shè)計(jì)的一種早期的運(yùn)輸協(xié)議。該協(xié)議通常被視為OSI無連接工作方式的源頭。TCP/IP仍在廣泛的使用，并且被稱為互聯(lián)網(wǎng)事實(shí)上的行業(yè)標(biāo)準(zhǔn)。TCP/IP有兩部分：TCP和IP。TCP表明是處于運(yùn)輸層，IP意為是網(wǎng)絡(luò)層。（1）運(yùn)輸層有兩個(gè)端到端協(xié)議，其中之一是傳輸協(xié)議（TCP），另一個(gè)是用戶數(shù)據(jù)報(bào)協(xié)議（UDP）。TCP是一種面向連接的協(xié)議，它可以在互聯(lián)網(wǎng)上無差錯(cuò)地將字節(jié)流從一臺(tái)機(jī)器發(fā)送出去。UDP是一種不可靠的無連接協(xié)議，用于不希望那種TCP流控制序列，而希望只提供自身功能的場(chǎng)合。（2）網(wǎng)絡(luò)層定義了正式的分組格式及稱為互聯(lián)網(wǎng)協(xié)議的IP。該網(wǎng)絡(luò)層的任務(wù)是將IP分組發(fā)送到指定的地方。圖14-3所示為TCP/IP參考模型。在運(yùn)輸層上面是應(yīng)用層。應(yīng)用層包括所有高層協(xié)議。早期的協(xié)議包括虛擬終IELNET、文件傳送協(xié)議FTP、電子郵件（SMTP）和域名服務(wù)DNS。3廣域網(wǎng)廣域網(wǎng)跨越地域很大，通常是一個(gè)國家或一個(gè)大陸。這種網(wǎng)絡(luò)中匯集了運(yùn)行各種用戶程序（即應(yīng)用程序）的計(jì)算機(jī)。本文還是沿用傳統(tǒng)的稱呼把它們叫做主機(jī)，在一些文獻(xiàn)里有時(shí)也稱其為端系統(tǒng)。這些主機(jī)是通過通信子網(wǎng)（有時(shí)簡(jiǎn)稱子網(wǎng)）連接起來的。子網(wǎng)的任務(wù)是把報(bào)文從一個(gè)主機(jī)傳送到另一個(gè)主機(jī)，就像電話系統(tǒng)把話音從講話人傳到收聽者一樣。把網(wǎng)絡(luò)（子網(wǎng)）的純通信任務(wù)與主機(jī)