局域網(wǎng)操作分析研究文獻翻譯

1、局域網(wǎng)操作分析研究網(wǎng)絡有兩類：局域網(wǎng)（lans）和廣域網(wǎng)（wan）。在這里主要談一下局域網(wǎng)。局域網(wǎng)就是在一個有限的地域范圍內(nèi)，典型的如在辦公大樓或校園中，將計算機及相關外設（如打印機）用電纜進行物理連結(jié)而組成的一個系統(tǒng)。網(wǎng)絡的拓撲結(jié)構(gòu)可以是環(huán)形的、星形的或總線形的。在局域網(wǎng)中，可用光纖或同軸電纜連結(jié)多臺計算機，且每臺計算機的硬盤上必須裝有專門的通信軟件。允許具有不同平臺的計算機共存于同一局域網(wǎng)中，且能進行數(shù)據(jù)交換的軟件早已開發(fā)出來了。局域數(shù)據(jù)網(wǎng)一般簡稱為局域網(wǎng)，用于在一幢樓內(nèi)或局限在樓群范圍內(nèi)把分散的基于計算機數(shù)據(jù)終端設備互連在一起。例如，一個局域網(wǎng)可以把一幢樓里或像大學校園內(nèi)各個樓里的各個辦

2、公室的工作站連在一起。另外，局域網(wǎng)也可以把分布在工廠或醫(yī)院建筑群中的計算機設備連在一起。由于所有這些設備都是一個單位的，因此局域網(wǎng)一般也由這個單位負責安裝和維護。于是這類局域網(wǎng)也叫做專用數(shù)據(jù)網(wǎng)。大多數(shù)廣域網(wǎng)，如公共電話交換網(wǎng)（pstn）就使用網(wǎng)狀（有時稱為網(wǎng)絡）拓撲結(jié)構(gòu)。而局域網(wǎng)，由于用戶數(shù)據(jù)終端設備相距很近，可采用簡單的拓撲結(jié)構(gòu)。常用的有星形、總線、環(huán)形和集線器等4種拓撲結(jié)構(gòu)。應用最廣的、用于本地計算機設備互連以進行數(shù)據(jù)通信的局域網(wǎng)拓撲結(jié)構(gòu)是集線器拓撲結(jié)構(gòu)。這種拓撲結(jié)構(gòu)是總線和環(huán)形拓撲結(jié)構(gòu)的變種。圖14-6展示了為這種拓撲結(jié)構(gòu)，有時也稱為集線器樹形拓撲結(jié)構(gòu)。局域網(wǎng)的傳輸媒體。雙絞線、同軸電纜

3、和光纖是局域網(wǎng)采用的3種主要傳輸媒體。局域網(wǎng)中采用了兩種媒體訪問控制技術。它們是用于總線網(wǎng)絡拓撲結(jié)構(gòu)的帶沖突檢測的載波偵聽多路存?。╟smacd）既可用于總線又可用于環(huán)形網(wǎng)絡的令牌控制技術。csma/ cd用來控制多路存取網(wǎng)絡上的每個站點在試圖發(fā)送信息前先“偵聽”，等待通路空閑。如果兩個站點在同一時刻要發(fā)送信息，將會檢測到?jīng)_突，這兩個站點必須各自“后退”一步，以后再重試。令牌控制是另一種用令牌去控制訪問共享傳輸媒體的方法。該令牌按所有連入媒體的dte都知道并遵守的一套確定的規(guī)則從一個dte傳向另一個dte。當某一dte掌握這一令牌時，它才能傳送一幀數(shù)據(jù)，而在傳送完該幀之后，要將令牌釋放，以便其

4、他dte訪問該傳輸媒體。文件服務器用于局域網(wǎng)。許多網(wǎng)絡稱為文件服務器的計算機來管理。文件服務器具有大容量的硬盤和一些用來管理對網(wǎng)上文件訪問的專門軟件。它控制著網(wǎng)上用戶如何共享數(shù)據(jù)和數(shù)據(jù)庫，以及用戶如何存取中央硬盤上的數(shù)據(jù)和應用軟件的主拷備。確保兩個用戶不能偶然地在同一時刻對同一文件進行更新或爭奪數(shù)據(jù)也是文件服務器的工作。文件服務器還可以管理對昂貴硬件（如激光打印機）的訪問。當文件服務器用于局域網(wǎng)時，大型數(shù)據(jù)庫就被存儲在服務器上，而且用戶也可以將其所有的工作文件存放在上面。這就像是一個人每天手工收集所有的數(shù)據(jù)，放到一個文件抽屜中，然后等需要時，再將這些數(shù)據(jù)發(fā)到工作人員手中。net ware局域網(wǎng)

5、操作系統(tǒng)。novell公司的net ware操作系統(tǒng)已經(jīng)成為ibm公司特有的網(wǎng)絡操作環(huán)境最強有力的競爭對手，它在對局域網(wǎng)絡的支持方面也早于ibm公司。事實上，除了自己的一部分軟件外，ibm公司也為所有的pc網(wǎng)和令牌環(huán)網(wǎng)購買了net ware操作系統(tǒng)。net ware操作系統(tǒng)的最主要部分是文件服務器軟件，服務器上的目錄被映射到網(wǎng)絡驅(qū)動器，這樣在用戶看來，它運行起來就如同是虛擬磁盤。它的服務器軟件是一個多任務的操作系統(tǒng)，文件結(jié)構(gòu)也與dos 2.x和dos 3.x的文件結(jié)構(gòu)一致。工作站上的 net ware外殼程序攔截了dos的21h中斷，并重新走向為對服務器的調(diào)用。net ware操作系統(tǒng)的主要優(yōu)

6、點是能夠運行在多種網(wǎng)絡硬件上。不論是選擇ibm網(wǎng)絡，corves公司的omninet網(wǎng)絡，還是att公司的星形局域網(wǎng)絡等，都可獲得net ware的操作環(huán)境。用局域網(wǎng)方式建立的通信線路和通過公用數(shù)據(jù)網(wǎng)連接的線路兩者的主要區(qū)別。因為局域網(wǎng)連接的設備之間相對來說距離較近，因而數(shù)據(jù)傳輸速率高得多。但是在iso的osi參考模型中，這種區(qū)別只在較低的與網(wǎng)絡相關的幾層比較明顯。而很多實例表明，在該參考模型高層協(xié)議中，這兩種網(wǎng)絡是沒有區(qū)別的。 附：英文原文：local area network csiec there are two categories of networks: local area ne

7、tworks (lans) and wide area networks (wans). here id like to mainly talk about lan.a lan is a system of computers and associated peripherals such as printers that are physically connected by cable within a limited geographical area-typically in an office building or on a college campus. the topology

8、 of the network may be ring, star or bus. lans use fiber optics or coaxial cable to connect computers, and each computer must have special communications software installed oil its hard disk. software has been developed that allows computers with different platforms to coexist and exchange data on t

9、he same lan.local area data networks，normally referred to simply as local area networks or lans，are used to interconnect distributed communities of computer-based dte located within a single building or localized group of buildingsfor example，a lan may be used to interconnect workstations distribute

10、d around offices within a single building or a group of buildings such as a university campusalternatively，it may be used to interconnect computer-based equipment distributed around a factory or hospital complex1since all the equipment is located within a single establishment，however，lans are normal

11、ly installed and maintained by the organizationhence they are also referred to as private data networksmost wide area networks，such as the pstn，use a mesh（sometimes referred to as a network）topologywith lans，however，the limited physical separation of the subscriber dte allows simpler topologies to b

12、e usedthe four topologies in common use are star，bus，ring and hubthe most widespread topology for lans designed to function as data communication subnet works for the interconnection of local computer-based equipment is the hub topology, which is a variation of the bus and ring4this is shown in fig.

13、 14-6，sometimes it is called hub/tree topologyits transmission media. twisted pair，coaxial cable and optical fiber are the three main types of transmission medium used for lanstwo techniques have been adopted for use of the medium access control in the lansthey are carrier-sense-multiple-access with

14、 collision detection（csmacd），for bus network topologies，and control token，for use with either bus or ring networks5csma / cd is used to control multiple-access networkseach on the network “l(fā)istens” before attempting to send a message，waiting for the “traffic” to clear6if two stations try to send the

15、ir messages at exactly the same time，a “collision” is detected，an both stations are required to “step back” and try latercontrol token is another way of controlling access to a shared transmission medium that is by the use of a control（pretension）tokenthis token is passed from one dte to another acc

16、ording to a defined set of rules understood and adhered to by all dte connected to the mediuma dte may only transmit a frame when it is in possession of the token and，after it has transmitted the frame，it passes the token on to allow another dte to access the transmission mediuma file server is used

17、 on a lan. many networks are managed by a computer called a file server. a file server has a largecapacity hard disk and special software that manages access to flies on the network. it controls how data and database are shared among users on the network and how users access master copies of data an

18、d application software on the centralized hard disk. it is the file servers job to make sure that users dont accidentally try to update a file at the same time and scramble the data. the file server may also manage the access to an expensive piece of hardware such as a laser printer. when a file ser

19、ver is used on a lan, large databases are stored on the server and users may store all of their work flies there as well. this operation is analogous to someones manually collecting all the data each day placing them in a file drawer, and then redistributing these data to the workers as needed.net w

20、are its the lan operating system. novells net ware has become the strongest competitor to ibms own network operating environment and predates ibm in its support for lans. in fact, ibm now markets net ware for both the pc network and for token ring in addition to its own software. the key to net ware

21、 is the file server software and directories on the server are mapped to network drives, thus operating like virtual diskettes from a users perspective. the server software is a multitasking operating system with a file structure consistent with dos 2.x and dos 3.x. the net ware shell in each workst

22、ation intercepts 21h dos calls and redirects appropriate calls to the server. perhaps the primary advantage of net ware is that it runs on a wide variety of networking hardware. regardless of whether you choose an ibm network, corves omninet, att star lan, etc., you can obtain net ware as the operat

23、ing environment. in fact, if you have one of each the user will not be able to tell the difference (unless there are some distinct performance differentials), and they can be interconnected through novells system of bridges and gateways. the main difference between a communication path established u

24、sing a lan and a connection made through a public data network is that a lan normally offers much higher data transmission rates because of the relatively short physical separations involved2in the context of the iso reference model for osi，however，this difference manifests itself only at the lower

25、network dependent layersin many instances the higher protocol layers in the reference model are the same for both types of networkfrom：戀愛運up一緒lets月亭方正！気持今flying get！dou都斗豆逗陡抖痘兜讀蚪竇篼蔸乧侸兠凟剅吺唗投斣枓梪橷毭氀浢瀆瀆瞗窬竇脰艔豆讀逾郖酘酡鈄鋀鈄閗闘阧餖饾斗鬦鬪鬬鬭du讀度毒渡堵獨肚鍍賭睹杜督都犢妒頓蠹篤嘟瀆櫝牘黷髑芏儥凟剢剫匵厾噣土涂妬嬻剬塅媏彖斷毈瑖碫篅籪緞專腶葮褍踹躖鍛鍴mr najib met search c

26、rews at pearce raaf base near perth on thursday morning, before their planes left for the day, and then later held talks with mr abbott.the disappearance of mh370 has tested our collective resolve, he told a news conference.faced with so little evidence, and such a herculean task, investigators from

27、 malaysia, the us, the uk, china, australia and france have worked without pause to reveal the aircrafts movements.he thanked both search teams and the australian government for their efforts in recent weeks, and said the search would go on.continue reading the main storymh370 - facts at a glance 8

28、march:malaysia airlines kuala lumpur-beijing flight carrying 239 people disappears planes transponder, which communicates with ground radar, was switched off as it left malaysian airspace satellite pings indicate plane was still flying seven hours after satellite contact was lost 24 march:based on n

29、ew calculations, malaysian pm says beyond reasonable doubt that plane crashed in southern indian ocean with no survivors what we know the search for flight mh370i know that until we find the plane, many families cannot start to grieve. i cannot imagine what they must be going through. but i can prom

30、ise them that we will not give up, he said.malaysian authorities have come in for heavy criticism over their management of the search, especially from relatives of the planes 153 chinese passengers.on thursday, eight military planes and nine ships were due to take part in the search.weather conditio

31、ns were fair, with visibility of approximately 10km (6 miles), the joint agency coordination centre (jacc) - which is overseeing the search - said.the british submarine hms tireless is also in the southern indian ocean and is due to be joined by royal navy ship hms echo.the australian navy ship ocea

32、n shield is heading to the region and has equipment for detecting the planes black-box flight recorder.experts say timing is critical as the flight recorder may only have enough battery power to send out a signal until 7 april.air chief marshall angus houston, head of the jacc, warned that the searc

33、h operation faced multiple difficulties.this is one of the most demanding and challenging search and rescue operations, or search and recovery operations, that i have ever seen and i think probably one of the most complex operations of this nature that the world has ever seen, he told mr najib and m

34、r abbott.on wednesday malaysian police chief khalid abu bakar said investigators had cleared all passengers of possible involvement in hijacking, sabotage or having personal or psychological problems that could have been connected to the disappearance.but he said that the criminal investigation coul

35、d go on and on and on. we have to clear every little thing.at the end of the investigations, we may not even know the real cause. we may not even know the reason for this incident, he added.the police chief said that more than 170 interviews had been conducted with family members of the pilots and c

36、rew members, and that even cargo and food served on the plane were being investigated in case ofdui對隊堆兌敦鐓碓懟憝兊兌垖埻塠奪奪対對嵟憞懟捶杸濧濻瀢瀩痽磓祋綐膭薱謉譈譵追鈗銳銳錞鎚鐓鐜銳陮隊頧鴭dul乧dun噸頓蹲墩敦鈍盾囤遁不躉沌盹鐓礅燉砘伅俊噸墪壿庉忳敦憞撉撴楯橔潡燉犜獤碷腞腯蜳豚踲蹾躉逇遯鈍鐓鐜頓驐duo多朵奪舵剁垛跺惰墮掇哆馱度躲踱沲咄鐸裰哚綞亸仛兊兌兌凙刴剟剫吋喥嚉嚲垜埵墮墯夛奪奲媠嫷尮崜嶞憜挅挆捶揣敓敚敠敪朶雜杕枤柁柂柮桗棰椯橢毲沰沱澤痥硾綞茤袳詑誃貀趓跢跥跿躱軃鄲鄲鈬錞鍺鐸鍺陀陊隋隋隓飿饳馱駄鬌鮵鵽點e餓哦額鵝蛾扼俄訛阿遏峨娥惡厄鄂鋨諤堊鍔閼萼苊軛婀莪鱷顎腭愕呃噩鶚屙亞亜亞偽佮侉偔偽偽僫匎匼卾吪呝咢咹啞唖啈啊啐啞惡囐囮埡埡堊堨堮妸妿姶娾娿媕屵岋峉峩崿庵廅悪惡戹搕搤搹擜曷枙椏櫮唉歞歹歺洝涐湂玀珴琧痷皒睋砈砐砨砵硆硪磀礘胺蒍蕚蘁蚅蝁覨訛咯誐諤譌讍豟軛軶輵迗遌遻邑鈋鋨鍔鑩閜閼阨阸隘頞頟額顎餓餩騀鬲魤魥鱷鰪鱷鴳鵈鵝