電子通信專業(yè)畢業(yè)論文外文翻譯--電信現代運營

1、<p><b>　　畢業(yè)設計</b></p><p><b>　?。ㄍ馕姆g材料）</b></p><p>　　Telecommunication Modern Operation</p><p><b>　　Telephone</b></p><p>　　In an

2、 analogue telephone network, the caller is connected to the person he wants to talk to by switches at various telephone exchanges. The switches form an electrical connection between the two users and the setting of these

3、 switches is determined electronically when the caller dials the number. Once the connection is made, the caller's voice is transformed to an electrical signal using a small microphone in the caller's handset. Th

4、is electrical signal is then sent through the network to the us</p><p>　　The fixed-line telephones in most residential homes are analogue — that is, the speaker's voice directly determines the signal'

5、;s voltage. Although short-distance calls may be handled from end-to-end as analogue signals, increasingly telephone service providers are transparently converting the signals to digital for transmission before convertin

6、g them back to analogue for reception. The advantage of this is that digitized voice data can travel side-by-side with data from the Internet and can be p</p><p>　　Mobile phones have had a significant impact

7、 on telephone networks. Mobile phone subscriptions now outnumber fixed-line subscriptions in many markets. Sales of mobile phones in 2005 totalled 816.6 million with that figure being almost equally shared amongst the ma

8、rkets of Asia/Pacific (204 m), Western Europe (164 m), CEMEA (Central Europe, the Middle East and Africa) (153.5 m), North America (148 m) and Latin America (102 m). In terms of new subscriptions over the five years from

9、 1999, Africa has</p><p>　　There have also been dramatic changes in telephone communication behind the scenes. Starting with the operation of TAT-8 in 1988, the 1990s saw the widespread adoption of systems b

10、ased on optic fibres. The benefit of communicating with optic fibres is that they offer a drastic increase in data capacity. TAT-8 itself was able to carry 10 times as many telephone calls as the last copper cable laid a

11、t that time and today's optic fibre cables are able to carry 25 times as many telephone calls as TAT</p><p>　　Assisting communication across many modern optic fibre networks is a protocol known as Asynch

12、ronous Transfer Mode (ATM). The ATM protocol allows for the side-by-side data transmission mentioned in the second paragraph. It is suitable for public telephone networks because it establishes a pathway for data through

13、 the network and associates a traffic contract with that pathway. The traffic contract is essentially an agreement between the client and the network about how the network is to handle th</p><p>　　Radio and

14、television</p><p>　　In a broadcast system, a central high-powered broadcast tower transmits a high-frequency electromagnetic wave to numerous low-powered receivers. The high-frequency wave sent by the tower

15、is modulated with a signal containing visual or audio information. The antenna of the receiver is then tuned so as to pick up the high-frequency wave and a demodulator is used to retrieve the signal containing the visual

16、 or audio information. The broadcast signal can be either analogue (signal is varied continuo</p><p>　　The broadcast media industry is at a critical turning point in its development, with many countries movi

17、ng from analogue to digital broadcasts. This move is made possible by the production of cheaper, faster and more capable integrated circuits. The chief advantage of digital broadcasts is that they prevent a number of com

18、plaints with traditional analogue broadcasts. For television, this includes the elimination of problems such as snowy pictures, ghosting and other distortion. These occur becau</p><p>　　In digital television

19、 broadcasting, there are three competing standards that are likely to be adopted worldwide. These are the ATSC, DVB and ISDB standards; the adoption of these standards thus far is presented in the captioned map. All thre

20、e standards use MPEG-2 for video compression. ATSC uses Dolby Digital AC-3 for audio compression, ISDB uses Advanced Audio Coding (MPEG-2 Part 7) and DVB has no standard for audio compression but typically uses MPEG-1 Pa

21、rt 3 Layer 2. The choice of modulation </p><p>　　However, despite the pending switch to digital, analogue receivers still remain widespread. Analogue television is still transmitted in practically all countr

22、ies. The United States had hoped to end analogue broadcasts on December 31, 2006; however, this was recently pushed back to February 17, 2009. For analogue television, there are three standards in use. These are known as

23、 PAL, NTSC and SECAM. For analogue radio, the switch to digital is made more difficult by the fact that analogue receivers</p><p>　　The Internet</p><p>　　The Internet is a worldwide network of c

24、omputers and computer networks that can communicate with each other using the Internet Protocol. Any computer on the Internet has a unique IP address that can be used by other computers to route information to it. Hence,

25、 any computer on the Internet can send a message to any other computer using its IP address. These messages carry with them the originating computer's IP address allowing for two-way communication. In this way, the I

26、nternet can be seen as a</p><p>　　An estimated 16.9% of the world population has access to the Internet with the highest access rates (measured as a percentage of the population) in North America (69.7%), Oc

27、eania/Australia (53.5%) and Europe (38.9%).In terms of broadband access, Iceland (26.7%), South Korea (25.4%) and the Netherlands (25.3%) lead the world. </p><p>　　The Internet works in part because of proto

28、cols that govern how the computers and routers communicate with each other. The nature of computer network communication lends itself to a layered approach where individual protocols in the protocol stack run more-or-les

29、s independently of other protocols. This allows lower-level protocols to be customized for the network situation while not changing the way higher-level protocols operate. A practical example of why this is important is

30、because it allows</p><p>　　For the Internet, the physical medium and data link protocol can vary several times as packets traverse the globe. This is because the Internet places no constraints on what physic

31、al medium or data link protocol is used. This leads to the adoption of media and protocols that best suit the local network situation. In practice, most intercontinental communication will use the Asynchronous Transfer M

32、ode (ATM) protocol (or a modern equivalent) on top of optic fibre. This is because for most intercon</p><p>　　At the network layer, things become standardized with the Internet Protocol (IP) being adopted fo

33、r logical addressing. For the world wide web, these “IP addresses” are derived from the human readable form using the Domain Name System (e.g. 72.14.207.99 is derived from www.google.com). At the moment, the most widely

34、used version of the Internet Protocol is version four but a move to version six is imminent. </p><p>　　At the transport layer, most communication adopts either the Transmission Control Protocol (TCP) or the

35、User Datagram Protocol (UDP). TCP is used when it is essential every message sent is received by the other computer where as UDP is used when it is merely desirable. With TCP, packets are retransmitted if they are lost a

36、nd placed in order before they are presented to higher layers. With UDP, packets are not ordered or retransmitted if lost. Both TCP and UDP packets carry port numbers with them</p><p>　　Above the transport l

37、ayer, there are certain protocols that are sometimes used and loosely fit in the session and presentation layers, most notably the Secure Sockets Layer (SSL) and Transport Layer Security (TLS) protocols. These protocols

38、ensure that the data transferred between two parties remains completely confidential and one or the other is in use when a padlock appears at the bottom of your web browser. Finally, at the application layer, are many of

39、 the protocols Internet users would be </p><p>　　Local area networks</p><p>　　Despite the growth of the Internet, the characteristics of local area networks (computer networks that run at most a

40、 few kilometres) remain distinct. This is because networks on this scale do not require all the features associated with larger networks and are often more cost-effective and efficient without them.</p><p>　

41、　In the mid-1980s, several protocol suites emerged to fill the gap between the data link and applications layer of the OSI reference model. These were Appletalk, IPX and NetBIOS with the dominant protocol suite during th

42、e early 1990s being IPX due to its popularity with MS-DOS users. TCP/IP existed at this point but was typically only used by large government and research facilities. As the Internet grew in popularity and a larger perce

43、ntage of traffic became Internet-related, local area networks</p><p>　　It is at the data link layer though that most modern local area networks diverge from the Internet. Whereas Asynchronous Transfer Mode (

44、ATM) or Multiprotocol Label Switching (MPLS) are typical data link protocols for larger networks, Ethernet and Token Ring are typical data link protocols for local area networks. These protocols differ from the former pr

45、otocols in that they are simpler (e.g. they omit features such as Quality of Service guarantees) and offer collision prevention. Both of these d</p><p>　　Despite the modest popularity of Token Ring in the 80

46、's and 90's, virtually all local area networks now use wired or wireless Ethernet. At the physical layer, most wired Ethernet implementations use copper twisted-pair cables (including the common 10BASE-T networks

47、). However, some early implementations used coaxial cables and some recent implementations (especially high-speed ones) use optic fibres. Optic fibres are also likely to feature prominently in the forthcoming 10-gigabit

48、Ethernet implem</p><p><b>　　電信現代運營</b></p><p><b>　　電話 </b></p><p>　　在一個模擬電話網絡, 來電者通過交換機與對方進行不同的電話交流?開關在兩用戶間形成一個電氣連接,其參數是由來電者按鍵時的電氣特性決定的? 一旦連接,來電者的聲音通過來電端處的電話

49、聽筒轉化為電信號?然后電信號通過網絡發(fā)送到另一端的用戶,并通過小型揚聲器將信號轉化為聲音?有一個單獨的電氣連接用于進行轉換,以使用戶交談? </p><p>　　固定電話 ,在多數居民區(qū)是模擬電話,那就是,發(fā)言者的聲音,直接決定著信號的電壓? 雖然距離短,來電可能會被作為模擬信號的端到端信號處理,越來越多電話服務供應商是適度的在傳輸前將模擬信號數字化以便傳輸,之后轉為模擬信號以便接收?它的優(yōu)勢是,數字化語音數據可

50、以從互聯網上以數字形式傳輸,而且可以完全轉載于遠程通信?(對比來看,模擬信號無可避免會受到噪聲影響?)</p><p>　　手機已對電話網絡產生了重大影響? 移動電話用戶現在在許多市場超過了固定線路用戶? 手機銷量在2005年總額為8.166億,被一下數字平分,其中亞洲/太平洋(2.04億),西歐(1.64億),cemea(中歐,中東和非洲)(1.535億),北美(1.48億)和拉丁美洲(1.02億)?在從199

51、9年之后的五年時間內新增用戶來看,非洲已以58.2 %的增長超過了其他地區(qū)的市場?手機逐漸采用如GSM或W-CDMA這些可以數字化傳輸語音信號的系統(tǒng),從而使AMPS這樣的模擬系統(tǒng)衰落?</p><p>　　電話通信也隱約地有了戲劇性的變化?開始運作的TAT-8(跨大西洋傳輸電纜)始于1988年, 20世紀90年代見證了基于光纖系統(tǒng)的普及?光纖傳輸的優(yōu)勢在于其所提供的數據容量的急劇增加?TAT-8可以傳輸相當于同軸

52、電纜電話10倍的數據,而現在的光纖能傳輸25倍于TAT-8的數據?數據能力的增加是由于幾個因素:第一,光纖體積遠小于其他競爭技術? 第二,他們不受到串擾這意味著數百條光纖可以很容易地捆綁在一個單一的電纜內?最后,復用技術的改善導致了單條光纖數據容量的指數增長?</p><p>　　基于現代光纖網絡的通信是一項稱為異步傳輸模式 ( ATM )的協(xié)議?如第二段所說,ATM協(xié)議允許為并排的數據傳輸?它適用于公共電話網絡

53、,因為它建立了通過網絡數據通道并以此進行通信?傳輸協(xié)議基本上是一個用戶與網絡之間的協(xié)議,它規(guī)定了網絡如何來處理數據;如果網絡不能滿足條件的傳輸協(xié)議,它不接受連接? 這很重要,因為電話可以通過協(xié)議,保證自己的恒定比特率,這將確保來電者的聲音,不是延遲的部分或完全切斷?ATM的競爭對手,如多標簽交換(MPLS),執(zhí)行類似的任務,并可望在未來取代ATM? </p><p><b>　　電臺和電視臺 </

54、b></p><p>　　在一個廣播系統(tǒng),中央高功率廣播塔傳輸高頻率的電磁波 ,到眾多的低功率接收器上?由廣播塔發(fā)送的高頻率波由信號調制且該信號載有視頻或音頻信息?接收天線稍作調整，以提取高頻率波,解調器用來恢復載有視力或音頻信息的信號?廣播信號可以是模擬(信號多種多樣,載有信息且連續(xù))或數字(信息作為一套離散值,可以編碼)? </p><p>　　廣播媒體業(yè)正處于發(fā)展中一個關鍵的轉

55、折點,許多國家都從模擬發(fā)展到數字廣播?此舉是可使生產更經濟,更快且更能夠集成電路 ?與傳統(tǒng)的模擬廣播相比,數字廣播最大的優(yōu)勢是,他們防止了一些投訴?對電視來說,這包括消除問題,如雪花屏,重影和其他失真? 這些發(fā)生原因,是因為模擬傳輸的性質,這意味著噪聲干擾會明顯影響最后的輸出?數字傳輸,克服了這個問題,因為接收時數字信號變?yōu)殡x散值,這樣小擾動不影響最終輸出?舉一個簡單的例子,一個二進制信息1011,已與信號的振幅[ 1.0 0.0 1.

56、0 1.0 ]調制,并收到信號的振幅[ 0.9 0.2 1.1 0.9 ]它將仍然解碼為二進制信息1011-一個完美原碼再現?從這個例子可以看出,數字傳輸也由一個問題,如果噪音足夠大,它可以大大改變解碼信息? 使用前向錯誤校正接收器可以在最終結果中糾正少數比特錯誤,但太多的噪音將導致難以理解的輸出,因此,傳輸失敗?</p><p>　　在數字電視廣播中,有3個相互競爭的標準,很可能是全世界公認的?它們是ATSC標

57、準,DVB標準和ISDB標準;通過這些標準,到目前為止,應用于標題地圖? 所有這三個標準,使用MPEG - 2 視頻壓縮? ATSC標準采用杜比數字AC - 3音頻壓縮,ISDB利用先進音頻編碼 ( MPEG - 2的第7部分),而DVB沒有音頻壓縮標準,但通常使用MPEG - 1第3部分第2層 ?不同標準所用的調制方式也有所不同?在數字音頻廣播中,標準更為統(tǒng)一,幾乎所有國家都選擇采用數字音頻廣播的標準(也稱為作為尤里卡147標準)?

58、也有例外,美國已選擇采用高清廣播?高清廣播,不同于尤里卡147 ,它是基于稱為在帶內通道傳輸的傳輸方法,這使數字化信息,進行“背馱式”AM或FM模擬傳輸?</p><p>　　然而,盡管數字化迫在眉睫,模擬接收機仍然普遍應用? 模擬電視仍然傳送幾乎所有國家?美國希望于2006年 12月31日之前結束模擬廣播;不過,最近又推到2009年 2月17日 ?對于模擬電視,有三個標準在使用中?它們是PAL制式 ,NTSC制

59、式和SECAM制式 ? 模擬電臺,切換到數字變得更加困難,因為模擬接收器只占數字接收機的一小部分成本?模擬電臺調制方式通常采用AM(幅度調制)或FM(頻率調制)?為實現立體聲播放 ,振幅調制副載波用于立體聲調頻 ? </p><p><b>　　互聯網 </b></p><p>　　互聯網是一個全球計算機組成的網絡,也是一種用IP聯系在一起的計算機網絡?在互聯網上的

60、任何一臺計算機都有一個唯一的IP地址,其他計算機可以用其進行路由選擇?因此,在互聯網上,任何一臺電腦可以通過IP地址傳送訊息給任何其他的計算機? 這些帶有計算機IP地址的信息,允許計算機之間雙向溝通?這樣一來,互聯網可以被看作是一個計算機之間信息的交換?</p><p>　　據估計,16.9 %的世界人口已經進入互聯網且具有最高訪問率(以人口百分比衡量),它們在北美地區(qū)(69.7 %),大洋洲/澳大利亞(53.5

61、%)和歐洲(38.9%)?在寬帶接入方面,冰島(26.7%),韓國(25.4%)和荷蘭(25.3 %)世界領先?</p><p>　　互聯網的成功,部分是因為協(xié)議管理計算機和路由器如何互相溝通? 計算機網絡通信本身的性質,有助于分層實現,此時,協(xié)議棧中的各個獨立協(xié)議或多或少獨立于其他協(xié)議?這使得低級別的協(xié)議適應網絡的情況,而不影響高層協(xié)議的實現?一個實際的例子可以說明它的重要性,因為它允許一個互聯網瀏覽器上運行相

62、同的代碼，不管運行的計算機連接到互聯網是通過以太網還是通過Wi - Fi連接?協(xié)議經常以其在OSI參考模型中的位置命名,1983年為第一步,也是一次不成功的嘗試,它試圖建立一個普遍采用的網絡協(xié)議套件?</p><p>　　對于互聯網來說,物理介質和數據鏈路層協(xié)議可以不同的數倍包遍歷全球? 這是因為互聯網對所用的物理介質或數據鏈路協(xié)議沒有限制?這導致媒體和協(xié)議的應用,它們最適合本地網絡的情況?在實踐中,多數洲際通訊

63、將使用異步轉移模式 ( ATM )協(xié)議(或一個現代的替代物)并輔以光纖? 這是因為,對于大多數的洲際通信來說,互聯網與公共交換式電話網絡一樣擁有相同的基礎設施? </p><p>　　在網絡層,適用于邏輯尋址的IP開始標準化?在萬維網上,這些“IP地址”來自通過域名系統(tǒng)處理的人類可讀格式(例如72.14.207.99是來自www.google.com)中?目前,使用最廣泛的版本的互聯網協(xié)議是版本4 ,但向版本六過

64、渡已是迫在眉睫?</p><p>　　在傳輸層大部分通信采用的是傳輸控制協(xié)議(TCP)或用戶數據報協(xié)議(UDP)? TCP是基本協(xié)議,每條來自其他計算機的消息均需采用TCP,而UDP只有在有利時才會被采用?有了TCP,數據包若在它們置于更高層次前丟失或亂序,它們會被重發(fā)?有了UDP,數據包丟失時會亂序,也不會重發(fā)? TCP和UDP數據包攜帶端口以便指出數據包應交由哪些應用程序或進程?因為某些應用級協(xié)議使用某些端口

65、 ,網絡管理員可以通過阻斷某一特定端口為目的端口的傳輸限制上網?</p><p>　　在傳輸層之上,有一些協(xié)議會用到并適當應用于會話層和表示層,最顯著的是安全套接層(SSL)和傳輸層安全 (TLS)協(xié)議? 這些協(xié)議,確保雙方之間傳輸的數據仍然完全保密并且一方或另一方在使用時,掛鎖出現于Web瀏覽器的底部?最后,在應用層,有很多的協(xié)議為互聯網用戶所熟悉,如HTTP ( Web瀏覽) , 的POP3 (電子郵件),F

66、TP (檔案傳輸),IRC (網上聊天),BitTorrent(文件共享)和OSCAR(即時通訊)? </p><p><b>　　局域網 </b></p><p>　　不看互聯網的發(fā)展, 僅局域網的特點 (運行于幾公里內的計算機網絡)仍然明顯?這是因為這種規(guī)模的網絡并不需要所有與較大的網絡有關的功能,因此往往更具成本效益和高效率? </p><p

67、>　　在二十世紀八十年代中期,幾個協(xié)議套件的出現,填補了OSI參考模型中數據鏈路層和應用層之間的空隙? 如AppleTalk,IPX和NetBios與20世紀90年代初占主導地位,因MS-DOS而廣受歡迎的協(xié)議套件IPX? 而TCP / IP,在這一點上,通常只用于大型政府和研究設施?隨著互聯網的受歡迎程度的增長以及較大的流量與互聯網逐漸相關,局域網逐步走向TCP / IP?今天的網絡大多用于TCP / IP流量是常見的?向TCP

68、 / IP的轉變由如允許的TCP / IP客戶發(fā)現自己的網絡地址的DHCP的技術支撐,而這與A ppleTalk,IPX/和N etBIOS協(xié)議套件以其成為標準? </p><p>　　在數據鏈路層,最現代的局域網偏離互聯網?而異步轉移模式(ATM)或多協(xié)議標簽轉換 (MPLS)技術是典型的數據鏈路協(xié)議,適用于較大的網絡?以太網和令牌環(huán)網是典型的局域網數據鏈路協(xié)議?這些協(xié)議不同于前協(xié)議,因為它們更簡單(例如,它們

69、省略了服務質量保證等功能) ,并提供碰撞預防?雙方的這些差異,是基于經濟成本的考慮?</p><p>　　盡管令牌環(huán)在80年代和90年代有了一定的普及,但是現在幾乎所有的局域網使用有線或無線以太網?在物理層,大多數有線以太網實現使用銅雙絞線電纜 (包括常用的10 Base-T的網絡)?然而,一些早期的實現使用同軸電纜,而最近的一些實現(特別是超高速的)使用光纖?光纖也可能在即將到來的10千兆以太網的實現中有著出色