局域网外文翻译一.docx

1、局域网外文翻译一外 文 翻 译论文题目：大型企业网络的设计与规划：贾龙飞学号：201120210230班级：1122102班年级：2011级专业：网络工程学院：软件学院指导教师：王志波（讲师）完成时间：二一五 年 四 月1.COMPUTER NETWORKS DATE COMMUNICATIONSThe end equipment which either generates the digital information for transmission or uses the received digital data can be computer ,printers ,keyboard

2、s, 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 transferred in parallel. Digital data, when transmitted, are in serial form. Parallel transmission of an 8-bit word require eig

3、ht 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 serial-to-parallel conversions for transmission and reception respectively and for data link management. The UART (Universal

4、Asynchronous Receiver/Transmitter) and USART (Universal Asynchronous/Asynchronous Receiver/Transmitter) are the devices that perform the parallel-to-serial and serial-to-parallel conversions. The primary DTE includes a line control unit (LCU or LinCo) which controls the flow of information in a mult

5、ipoint 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 communications equipment owned and maintained by Telco property.Data communications equipment (DCE) accepts the serial dat

6、a 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 converting the received analog signal to a serial digital data stream. The simplest form of DCE is a modem (modulator/demod

7、ulator) 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-digital converter. The most common of modulation by modems are frequency shift keying (FSK), phase shift keying (PSK), and quad

8、rature 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 “Digital T-carrier”), a pulse Code Modulation (PCM) equipment must be used. A microwave transmission system can also be used

9、 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 were left unregulated, the variations generated would probably be proportional to the number of manufacturers. Electronics i

10、ndustries 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 levels. The RS-232C is anticipated to be replaced by an update standard.2.ARCHITECTURE OF COMPUTER NETWORKSComputer network

11、 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 logical structure should comply with a set of design principles, including the organization of functions and the description of

12、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 we will discuss two important network architectures, the OSI reference model and the TCP/IP reference model.1.The OSI Refere

13、nce 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 first step toward international standardization of the protocols used in the various layers. The model is called the ISO OSI (

14、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 just call it the OSI model for short.The OSI model has seven has seven layers. Note that the OSI model itself is not a netwo

15、rk architecture because it does not specify the exacts and protocols to be used in each layer. It just tells what each layer should do. However , However, ISO has also produced standards for all the layers, although these are not part of the reference model itself. Each one has been published as a s

16、eparate 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 (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 pa