計算機畢設(shè)外文翻譯

1、外文翻譯原文及譯文學(xué) 院計算機學(xué)院專 業(yè)班 級學(xué) 號姓 名指導(dǎo)教師負責(zé)教師沈陽航空航天大學(xué)2011年6月Introduction to TCP/IPABSTRACTTCP and IP were developed by a Department of Defense (DOD) research project to connect a number different networks designed by different vendors into a network of networks (the Internet). It was initially successful be

2、cause it delivered a few basic services that everyone needs (file transfer, electronic mail, remote logon) across a very large number of client and server systems. Several computers in a small department can use TCP/IP (along with other protocols) on a single LAN. The IP component provides routing f

3、rom the department to the enterprise network, then to regional networks, and finally to the global Internet. On the battlefield a communications network will sustain damage, so the DOD designed TCP/IP to be robust and automatically recover from any node or phone line failure. This design allows the

4、construction of very large networks with less central management. However, because of the automatic recovery, network problems can go undiagnosed and uncorrected for long periods of time. As with all other communications protocol, TCP/IP is composed of layers: IP - is responsible for moving packet o

5、f data from node to node. IP forwards each packet based on a four byte destination address (the IP number). The Internet authorities assign ranges of numbers to different organizations. The organizations assign groups of their numbers to departments. IP operates on gateway machines that move data fr

6、om department to organization to region and then around the world. TCP - is responsible for verifying the correct delivery of data from client to server. Data can be lost in the intermediate network. TCP adds support to detect errors or lost data and to trigger retransmission until the data is corre

7、ctly and completely received. Sockets - is a name given to the package of subroutines that provide access to TCP/IP on most systems. 1 IntroductionThe Army puts out a bid on a computer and DEC wins the bid. The Air Force puts out a bid and IBM wins. The Navy bid is won by Unisys. Then the President

8、decides to invade Grenada and the armed forces discover that their computers cannot talk to each other. The DOD must build a network out of systems each of which, by law, was delivered by the lowest bidder on a single contract. The Internet Protocol was developed to create a Network of Networks (the

9、 Internet). Individual machines are first connected to a LAN (Ethernet or Token Ring). TCP/IP shares the LAN with other uses (a Novell file server, Windows for Workgroups peer systems). One device provides the TCP/IP connection between the LAN and the rest of the world. To insure that all types of s

10、ystems from all vendors can communicate, TCP/IP is absolutely standardized on the LAN. However, larger networks based on long distances and phone lines are more volatile. In the US, many large corporations would wish to reuse large internal networks based on IBMs SNA. In Europe, the national phone c

11、ompanies traditionally standardize on X.25. However, the sudden explosion of high speed microprocessors, fiber optics, and digital phone systems has created a burst of new options: ISDN, frame relay, FDDI, Asynchronous Transfer Mode (ATM). New technologies arise and become obsolete within a few year

12、s. With cable TV and phone companies competing to build the National Information Superhighway, no single standard can govern citywide, nationwide, or worldwide communications. The original design of TCP/IP as a Network of Networks fits nicely within the current technological uncertainty. TCP/IP data

13、 can be sent across a LAN, or it can be carried within an internal corporate SNA network, or it can piggyback on the cable TV service. Furthermore, machines connected to any of these networks can communicate to any other network through gateways supplied by the network vendor.2.1 AddressesEach techn

14、ology has its own convention for transmitting messages between two machines within the same network. On a LAN, messages are sent between machines by supplying the six byte unique identifier (the MAC address). In an SNA network, every machine has Logical Units with their own network address. DECNET,

15、Appletalk, and Novell IPX all have a scheme for assigning numbers to each local network and to each workstation attached to the network. On top of these local or vendor specific network addresses, TCP/IP assigns a unique number to every workstation in the world. This IP number is a four byte value t

16、hat, by convention, is expressed by converting each byte into a decimal number (0 to 255) and separating the bytes with a period. For example, the PC Lube and Tune server is 34. An organization begins by sending electronic mail to HostmasterINTERNIC.NET requesting assignment of a network

17、 number. It is still possible for almost anyone to get assignment of a number for a small Class C network in which the first three bytes identify the network and the last byte identifies the individual computer. The author followed this procedure and was assigned the numbers 192.35.91.* for a networ

18、k of computers at his house. Larger organizations can get a Class B network where the first two bytes identify the network and the last two bytes identify each of up to 64 thousand individual workstations. Yales Class B network is 130.132, so all computers with IP address 130.132.*.* are connected t

19、hrough Yale. The organization then connects to the Internet through one of a dozen regional or specialized network suppliers. The network vendor is given the subscriber network number and adds it to the routing configuration in its own machines and those of the other major network suppliers. There i

20、s no mathematical formula that translates the numbers 192.35.91 or 130.132 into Yale University or New Haven, CT. The machines that manage large regional networks or the central Internet routers managed by the National Science Foundation can only locate these networks by looking each network number

21、up in a table. There are potentially thousands of Class B networks, and millions of Class C networks, but computer memory costs are low, so the tables are reasonable. Customers that connect to the Internet, even customers as large as IBM, do not need to maintain any information on other networks. Th

22、ey send all external data to the regional carrier to which they subscribe, and the regional carrier maintains the tables and does the appropriate routing. New Haven is in a border state, split 50-50 between the Yankees and the Red Sox. In this spirit, Yale recently switched its connection from the M

23、iddle Atlantic regional network to the New England carrier. When the switch occurred, tables in the other regional areas and in the national spine had to be updated, so that traffic for 130.132 was routed through Boston instead of New Jersey. The large network carriers handle the paperwork and can p

24、erform such a switch given sufficient notice. During a conversion period, the university was connected to both networks so that messages could arrive through either path. 2.2 SubnetsAlthough the individual subscribers do not need to tabulate network numbers or provide explicit routing, it is conveni

25、ent for most Class B networks to be internally managed as a much smaller and simpler version of the larger network organizations. It is common to subdivide the two bytes available for internal assignment into a one byte department number and a one byte workstation ID. The enterprise network is built

26、 using commercially available TCP/IP router boxes. Each router has small tables with 255 entries to translate the one byte department number into selection of a destination Ethernet connected to one of the routers. Messages to the PC Lube and Tune server (34) are sent through the nationa

27、l and New England regional networks based on the 130.132 part of the number. Arriving at Yale, the 59 department ID selects an Ethernet connector in the C& IS building. The 234 selects a particular workstation on that LAN. The Yale network must be updated as new Ethernets and departments are added,

28、but it is not effected by changes outside the university or the movement of machines within the department. 2.3 A Uncertain PathEvery time a message arrives at an IP router, it makes an individual decision about where to send it next. There is concept of a session with a preselected path for all tra

29、ffic. Consider a company with facilities in New York, Los Angeles, Chicago and Atlanta. It could build a network from four phone lines forming a loop (NY to Chicago to LA to Atlanta to NY). A message arriving at the NY router could go to LA via either Chicago or Atlanta. The reply could come back th

30、e other way. How does the router make a decision between routes? There is no correct answer. Traffic could be routed by the clockwise algorithm (go NY to Atlanta, LA to Chicago). The routers could alternate, sending one message to Atlanta and the next to Chicago. More sophisticated routing measures

31、traffic patterns and sends data through the least busy link. If one phone line in this network breaks down, traffic can still reach its destination through a roundabout path. After losing the NY to Chicago line, data can be sent NY to Atlanta to LA to Chicago. This provides continued service though

32、with degraded performance. This kind of recovery is the primary design feature of IP. The loss of the line is immediately detected by the routers in NY and Chicago, but somehow this information must be sent to the other nodes. Otherwise, LA could continue to send NY messages through Chicago, where t

33、hey arrive at a dead end. Each network adopts some Router Protocol which periodically updates the routing tables throughout the network with information about changes in route status. If the size of the network grows, then the complexity of the routing updates will increase as will the cost of trans

34、mitting them. Building a single network that covers the entire US would be unreasonably complicated. Fortunately, the Internet is designed as a Network of Networks. This means that loops and redundancy are built into each regional carrier. The regional network handles its own problems and reroutes m

35、essages internally. Its Router Protocol updates the tables in its own routers, but no routing updates need to propagate from a regional carrier to the NSF spine or to the other regions (unless, of course, a subscriber switches permanently from one region to another).2.4 Undiagnosed ProblemsIBM desig

36、ns its SNA networks to be centrally managed. If any error occurs, it is reported to the network authorities. By design, any error is a problem that should be corrected or repaired. IP networks, however, were designed to be robust. In battlefield conditions, the loss of a node or line is a normal cir

37、cumstance. Casualties can be sorted out later on, but the network must stay up. So IP networks are robust. They automatically (and silently) reconfigure themselves when something goes wrong. If there is enough redundancy built into the system, then communication is maintained. In 1975 when SNA was d

38、esigned, such redundancy would be prohibitively expensive, or it might have been argued that only the Defense Department could afford it. Today, however, simple routers cost no more than a PC. However, the TCP/IP design that, Errors are normal and can be largely ignored, produces problems of its own

39、. Data traffic is frequently organized around hubs, much like airline traffic. One could imagine an IP router in Atlanta routing messages for smaller cities throughout the Southeast. The problem is that data arrives without a reservation. Airline companies experience the problem around major events,

40、 like the Super Bowl. Just before the game, everyone wants to fly into the city. After the game, everyone wants to fly out. Imbalance occurs on the network when something new gets advertised. Adam Curry announced the server at and his regional carrier was swamped with traffic the next day. The probl

41、em is that messages come in from the entire world over high speed lines, but they go out to over what was then a slow speed phone line. Occasionally a snow storm cancels flights and airports fill up with stranded passengers. Many go off to hotels in town. When data arrives at a congested router, the

42、re is no place to send the overflow. Excess packets are simply discarded. It becomes the responsibility of the sender to retry the data a few seconds later and to persist until it finally gets through. This recovery is provided by the TCP component of the Internet protocol. TCP was designed to recov

43、er from node or line failures where the network propagates routing table changes to all router nodes. Since the update takes some time, TCP is slow to initiate recovery. The TCP algorithms are not tuned to optimally handle packet loss due to traffic congestion. Instead, the traditional Internet resp

44、onse to traffic problems has been to increase the speed of lines and equipment in order to say ahead of growth in demand. TCP treats the data as a stream of bytes. It logically assigns a sequence number to each byte. The TCP packet has a header that says, in effect, This packet starts with byte 3796

45、42 and contains 200 bytes of data. The receiver can detect missing or incorrectly sequenced packets. TCP acknowledges data that has been received and retransmits data that has been lost. The TCP design means that error recovery is done end-to-end between the Client and Server machine. There is no fo

46、rmal standard for tracking problems in the middle of the network, though each network has adopted some ad hoc tools. 3 Need to KnowThere are three levels of TCP/IP knowledge. Those who administer a regional or national network must design a system of long distance phone lines, dedicated routing devi

47、ces, and very large configuration files. They must know the IP numbers and physical locations of thousands of subscriber networks. They must also have a formal network monitor strategy to detect problems and respond quickly. Each large company or university that subscribes to the Internet must have

48、an intermediate level of network organization and expertise. A half dozen routers might be configured to connect several dozen departmental LANs in several buildings. All traffic outside the organization would typically be routed to a single connection to a regional network provider. However, the en

49、d user can install TCP/IP on a personal computer without any knowledge of either the corporate or regional network. Three pieces of information are required: 1.The IP address assigned to this personal computer The part of the IP address (the subnet mask) that distinguishes other machines on the same

50、 LAN (messages can be sent to them directly) from machines in other departments or elsewhere in the world (which are sent to a router machine) 2.The IP address of the router machine that connects this LAN to the rest of the world. 3.In the case of the PCLT server, the IP address is 34. S

51、ince the first three bytes designate this department, a subnet mask is defined as (255 is the largest byte value and represents the number with all bits turned on). It is a Yale convention (which we recommend to everyone) that the router for each department have station number 1 within

52、 the department network. Thus the PCLT router is . Thus the PCLT server is configured with the values: My IP address: 34 Subnet mask: Default router: The subnet mask tells the server that any other machine with an IP address beginning 130.132.59.* i

53、s on the same department LAN, so messages are sent to it directly. Any IP address beginning with a different value is accessed indirectly by sending the message through the router at (which is on the departmental LAN). Additional information is available in self-study courses from SRA (

54、1-800-SRA-1277) TCP/IP 34610 Copyright 1995 PCLT - Introduction to TCP/IP - H. Gilbert TCP/IP的介紹說明摘 要TCP/IP是由美國國防部（DOD）開發(fā)的一個研究項目，用以將不同的網(wǎng)絡(luò)廠商設(shè)計的不同網(wǎng)絡(luò)連接到由許多網(wǎng)絡(luò)組成的一個網(wǎng)絡(luò)中（即“互聯(lián)網(wǎng)”）。它取得了初步的成功，因為它通過穿越大量的客戶機與服務(wù)器系統(tǒng)向人們提供了一些基本的需求服務(wù)（如文件傳輸?shù)幕痉?wù)，電子郵件，遠程登錄）。在一個單一局域網(wǎng)中一個小部門多臺計算機可以使用TCP/IP（同其他協(xié)議）。IP組件提供的路由可以從部門到企業(yè)網(wǎng)絡(luò)，然后再到區(qū)

55、域網(wǎng)絡(luò)，并最終接入全球互聯(lián)網(wǎng)。在戰(zhàn)場上，通信網(wǎng)絡(luò)將面臨被破壞的危險，因此，美國國防部設(shè)計的TCP/IP要很健全穩(wěn)定，并能從任何節(jié)點或電話線路故障中自動恢復(fù)。這樣的設(shè)計允許在較少的中央控制下組建龐大的網(wǎng)絡(luò)。此外，由于自動恢復(fù)機制，網(wǎng)絡(luò)問題可以在很長一段時間內(nèi)不被進行問題診斷和錯誤糾正。 正如其他所有通信協(xié)議，TCP/IP協(xié)議是由多個層組成的： IP - 負責(zé)將數(shù)據(jù)包從一個節(jié)點移動到另一個節(jié)點。每個數(shù)據(jù)包的IP轉(zhuǎn)發(fā)基于四字節(jié)的目的地址（IP地址）?；ヂ?lián)網(wǎng)管理機構(gòu)對不同地區(qū)組織分配了一定數(shù)量的IP地址。各地區(qū)組織將他們所擁有的地址劃分成數(shù)個組再分配到各個部門。IP運行在被稱為網(wǎng)關(guān)的機器上面，而網(wǎng)關(guān)的

56、作用是將數(shù)據(jù)包層層轉(zhuǎn)發(fā)，從部門到組織再到地區(qū)最后送達全世界。TCP - 負責(zé)核查從客戶傳送到服務(wù)器的數(shù)據(jù)正確性。數(shù)據(jù)在傳遞時可能會在中間的網(wǎng)絡(luò)發(fā)生丟失。TCP增加了對錯誤以及丟失數(shù)據(jù)的檢測并且能在發(fā)生問題時激活數(shù)據(jù)重傳機制直到數(shù)據(jù)被正確和完整的接收。Sockets - 是一個數(shù)據(jù)包子程序的名稱，該子程序能提供在大多數(shù)系統(tǒng)上接入TCP/IP的功能。1引言美國陸軍提出了一個計算機上系統(tǒng)上的競標由DEC公司贏得。美國空軍也提出一個競標并由IBM公司贏得。而美國海軍的競標則由Unisys公司贏得。當(dāng)美國總統(tǒng)決定入侵格林納達時，美國軍方發(fā)現(xiàn)他們的陸?？杖姼髯运鶕碛械挠嬎銠C不能與其他軍種的計算機相互通信

57、。因此，美國國防部必須建立一個網(wǎng)絡(luò)體系，它不依賴于陸?？杖姼髯愿鶕?jù)法律法規(guī)由最低競價者按照合同所交付的計算機系統(tǒng)。開發(fā)Internet協(xié)議是為了建立一個將許多不同網(wǎng)絡(luò)集合在一起的網(wǎng)絡(luò)（以下簡稱“互聯(lián)網(wǎng)”）。獨立的機器都首先連接到局域網(wǎng)（以太網(wǎng)或令牌環(huán)）。 TCP/IP協(xié)議與其他應(yīng)用共同使用局域網(wǎng)（如Novell文件服務(wù)器，Windows for Workgroups的對等系統(tǒng)）。一臺設(shè)備在局域網(wǎng)和世界的剩余地區(qū)提供TCP/IP連接。為了確保所有供應(yīng)商的所有類型的系統(tǒng)可以彼此相互溝通，TCP/IP協(xié)議是局域網(wǎng)上的絕對標準。不過，基于長途電話線介質(zhì)基礎(chǔ)上的較大網(wǎng)絡(luò)更加不穩(wěn)定。在美國，許多大公司希

58、望重新使用以IBM的SNA為基礎(chǔ)的龐大的內(nèi)部網(wǎng)絡(luò)。在歐洲，國家通信公司傳統(tǒng)上以X.25為標準。然而，隨著高速微處理器、光纖以及數(shù)字電話系統(tǒng)的迅猛發(fā)展產(chǎn)生了一些新的選擇：綜合業(yè)務(wù)數(shù)字網(wǎng)（ISDN），幀中繼，光纖分布式數(shù)據(jù)介面（FDDI），異步傳輸模式（ATM）。新技術(shù)誕生并在幾年內(nèi)就成為了過時產(chǎn)品。隨著有線電視和電話公司競相建立國家信息高速公路，沒有一個標準可以統(tǒng)治全市，全國或全球通信。TCP/IP將眾多網(wǎng)絡(luò)再次組合成為一個網(wǎng)絡(luò)，在當(dāng)今技術(shù)存在不確定性的條件下，TCP/IP的原始設(shè)計是非常適合的。TCP/IP數(shù)據(jù)可以通過局域網(wǎng)發(fā)送，也可以在企業(yè)SNA網(wǎng)絡(luò)內(nèi)部被傳輸，也可以搭載在有線電視服務(wù)網(wǎng)上。

59、此外，接入這些網(wǎng)絡(luò)的機器設(shè)備可以在網(wǎng)絡(luò)供應(yīng)商提供支持的情況下通過網(wǎng)關(guān)與其他任何網(wǎng)絡(luò)進行通信交流。2.1地址每一項技術(shù)都有其自己的公約使兩臺機器在同一個網(wǎng)絡(luò)內(nèi)的傳遞信息。在一個局域網(wǎng)內(nèi)，根據(jù)所提供的六字節(jié)唯一標示符（即網(wǎng)卡物理地址MAC）使得消息在機器設(shè)備之間傳遞。在一個SNA網(wǎng)絡(luò)，每一臺機器擁有自己的網(wǎng)絡(luò)地址邏輯單元。 DECNET，AppleTalk以及Novell IPX都一套體系用來給每個本地網(wǎng)絡(luò)以及接入網(wǎng)絡(luò)的每一個工作站分配地址。在這些地方或供應(yīng)商特定的網(wǎng)絡(luò)地址中，TCP/IP給全球每一個工作站分配一個獨一無二的地址。這種“IP地址”是一個4字節(jié)的值，按照約定，每一個字節(jié)通過將其轉(zhuǎn)變成一個范圍從0到255的十進制數(shù)來表示，并且每一個字節(jié)通過句點