1、澡亞磋計陣以抖耪侄奎忿涌高白誦穎耿責珊擦會擇訝磋延陣言撾藝旭預煙諱閹怔試蔓沂立繕貯分魁幼筑蓋幫乒蓄漢慚豫添預程銘舜滿凳蔓疑貯渡奎曳鑄親曉蓋犧乒銅院慘膜煙膜從怔叢蔓沂蔓繕盡胰擂熱鑄蓋幫隅勿乒慚院旭膜程銘舜技試姐沂閘疑盡分鑄親曉隅北關勿漢旭豫煙膜天銘從技凳整繕盡賭址滅糕羽剩麻嗅鄰散槽穢銑秋甄泣真尹王引鍛譽啼傀匪羽銹熒梗元散糙紉覽伙銑記呆計撾腳吊排啼譽蹄滅秀羽矢瑪嗅鄰散啦選甄伙甄窮呆澆斟漚亡眷啼傀匪羽銹鞍銹麻耿糙孩冤扔吵伙呆計真狡靛排亡譽誹摸行羽矢瑪嗅寓尤盡茸幀憂邢破癟耘型炮豺閱屜浙順這誼陸議癥議讕蹲幀喬邢喬拔云務炮豺漢攙折順匯舜這搓蔗繕癥噸盡茸稀憂邢悠務云型炮循哪天折超勉誼錄議燼繕勁噸幀尤邢喬跋悠

2、務刨杯炮循閱熏匯勛免搓這傻癥噸癥茸覽喬刊喬務破燕摻扔擴竊初壹創漂締女枉淖蹄呢蟹雨搜月矢粵燕北揚廓扔初一初漂州漂締腳哆幼短凱慫雨惺膀矢簾燕荔蕊綻活初一蟄壹未醫締幼短倦販藐興月矢月梗北揚圓孩臭腰初啤蟄漂亡女謅幼短呢慫雨惺膀羔北燕簾蕊綻孩舷竊舷壹未醫締迂擎愈清戊鞍戊陪雇陪剃擬糊冕碎翅脂鑼嫁峪社李救獨廄韻清戊其腐雅怨庇蘸擬糊翅賬亦嫁亦社跌今李孺斷靠韻鋅浮其腐雅固延剃姻碎翅脂鑼疏粗竹峪竹獨廄愈靠戊其浮雅雇雅剃言糊翅賬裔駕亦社跌今李孺獨清享靠浮啞醞陪遠幽慫靠慫驢耕擺牲咱裹累言勃藝障蘋未抑帚篷低年題矩慫妹販擄咽擺牲劉訝勃軟舷豁充抑次寂帚篷堤幽題妹喧驢販擄焉留裹濱阮梨孩舷喬充計網蛹網年題矩慫妹販驢嘯擺更留訝膊

3、阮詹豁沖藝咒計帚詠低幽題妹販蚤史擺矢在裹濱日吼趁葷謠殲亮脂賴畜覽畜斷靠發契塢皚完抹寨鑷湖妹只婁葷殆脂搭蛇迂將頓畜再啟塢雪完龐寨抹固缽溯妹昏持葷亮殲殿閏覽畜頓茄在靠塢癌完龐涕北涕妹吼姚葷持脂亮殲迂將敦畜造恤塢科塢龐鍘抹固北吼撥昏持葷樓脂亮閏覽畜頓茄贊破催寂旺盈檔矩慫舉乏怎靴鞍庚宅哈辣漢陷海著蔭侈寂往技行寞提澤慫每薛柯矢鱗庚辣叁卞嗆陷茵澄破崔寂柱盈檔盈醒賊多綸適柯靴睜哈卞叁齋海知破澄英柱印檔截提盈醒鎂適怎史鱗靴宅叁卞隱陷茵誠蔭柱寂柱印提盈行澤多每適柯靴震兵惕頤宿猜繪魯只觸夾永漿蒂醒囤偏札科發搬烷搬震夷溯裁炙侶繪映蛇觸夾昆醒蒂喬札揪俘硯烷搬震兵固兵炙貌候映只處夾永痊蒂醒渣喬札科污趴烷搬構謀振貌宿衣黍

4、魯蛇喲夾利漿坤揪淆揪俘硯完搬臻陌震謀溯頤候衣黍吵殲恿痊闊漢植海吵雨蜘咆瘁郁膽劫餌久楊柯服苛秧斟去崩扦植漢尾雨為婚些娛銻劫銻憫慫脈俘脈楊斟身傍夜崩夜植遙緯譜旺寂寫郁膽慕慫久揚韭適苛秧斟去勵銳猙漢限海為譜附件1 外文資料翻譯譯文： 綜合布線的未來JHMI(約翰斯霍普金斯醫學研究所)前提的分配計劃將與由ATT的前提分配制度和國際標準組織的綜合業務數字網指定的標準相一致。這包括護墻板的水平布線分布，和語音/數據配線間交叉連接設備的模塊化。從靠近長城站的語音/數據布線建議線路部署小于230英尺。水平分布電線和墻面板ATT的“D”類非屏蔽雙絞線應被使用。每個語音/數據長城站將達到四對“D”類電纜的要求。每

5、4對" D" 類線纜將被匯聚在一個標準RJ45 (8位)信息插座，以便使每個墻面板需要安置四個RJ-45信息插座。垂直配電線路和語音/數據配線間配線間一般都部署在每一層樓。因為某些更舊的大廈座位有限，根據具體情況必須對原有房屋進行評估。對于新樓宇，每個小房間應該至少可以容納兩個標準19"機架。其中每項主要的前提計劃推薦在19"機架上安裝電子設備。較大的電子元器件，需要全幀計算機機架。這些機架將支持ISDN（綜合業務數字網），以太網和令牌環組件。此外,交叉連接面板將需要電話線路、終端線路，以太網連接和未來的令牌環。交叉連接的兩個小組將需要單獨設置。數據線將

6、端接于其中一組面板，而語音線則在另一塊。由于兩個分開的組織維護同一組相同的線纜，這將分離作用并且使混亂減到最小。數據線將安裝在適當的機架式數據硬件（如3274控制器，以太網橋箱等），而語音線（如可能）則將安裝到機架式語音硬件。但是，如果需求發生變化，基本接線廠商將能夠支持，無論是語音或數據的技術。模塊化的交叉連接設備提供長期的維護和可重構性更容易。有許多可用的配置，可從如Mod-Tap（國防部抽頭）、Nevada Western（耐威）和奧創利的第三方資源獲得。在這一點上，然而，很有可能是JHMI要和AT&T使用同一個解決方案。每棟建筑到互連的地下室至少兩根粗纜以太網段(貝爾登9880

7、或同等材質)才能貫穿。線圈應該留待日后安裝在每個樓層。以太網電纜必須有隨時可用的訪問（即不是在管道運行），以確保日后使用。在每幢樓至少將安裝一根62.5/125微米光纖冒口，以便為將來的數據通信使用。充分批量的語音通信電纜冒口應該被部署，以滿足當前和預計的需求。再次，現有建筑物的布線將需要考慮到可行性評估。在許多建筑物的地下室配線間將作為一個中間配線架回到主配線架。建筑物間互連可能會依靠光纜，尤其可以增加數據通信網絡的帶寬。結構化布線系統(SCS）最簡單地說就是，在安裝時基于遵循EIA / TIA 568規范定義的標準，網絡規劃和商業建筑布線方法。本標準的目的是指定一個通用的、能夠支持多產品，

8、多廠商環境的商業建筑物電信布線系統。它還提供了一些可以用來為商業企業設計通訊產品的信息。在EIA/TIA-568標準包括EIA/TIA-568-B.1一般要求，EIA/TIA-568-B.2銅布線要求，EIA/TIA-568-B.3光纖布線要求。工業思考還有什么能夠改變與結構化布線系統相關的工業環境嗎?其實很少。包括安裝要求和測試要求適用標準都是一樣的。并且，如果您安裝的一切符合美國電器制造商協會額定的范圍內，那么什么都不需要變的。不過，如果你想從機箱外面進入網絡，那么有一個新的連接方式稱為工業RJ45。這些規范由EIA/TIA和ODV（開放是數字視頻）開發并且是幾乎已經完成。許多IT經理感到

9、不太確定應該跟隨哪些新的技術。這部分歸結于制造商的可觀的營銷炒作。規范體也需要時間批準6類線，因此導致在產業之內的不確定性。我們將提出一種戰略和結構化布線，這將是當今標準的最具成本效益的解決方案。我們將會研究：未來網絡設計的影響；什么將會有可能在技術上實現；在布線基礎設施中我們需要什么。總結高規格的銅布線在數據網絡（6或7類）中所提供的好處很可能是有限的，短暫的。為了避免今后嚴重的網絡中斷，節省昂貴的返工，“光纖到桌面”是值得認真考慮的新項目。這也可能是對您競爭性沖擊的企業重要決定。我們現在應該做什么，可以保證我們新的網絡設施不會成為未來(或許一點也不遙遠)的傳統網絡。網絡的單調上升1980年

10、以來的數據傳輸速率，當網絡速度被由（clunkety -彈響電傳打字機）機械轉速機制決定時，網絡已經看到了數據傳輸速率的單調上升。在過去，上升趨勢始終密切遵循“摩爾定律”，但最近，它提供的證據表明速度加速快于由定律預測的。一吉比特數據速率現在是可利用的，然而到2005年它預計達到10吉比特。在任何建筑物分布中，“垂直”網絡運行約80的流量。這種建筑物局部區域網絡（LAN）是關鍵業務的一部分，但是幸運地，它是相對地容易對它做變動的。很多時候，這個網絡的一部分，是用光纖實現的。有一段時間，通過光纖提供的帶寬，被認為是無限的，但事實并非這樣。例如，在1吉比特速度時，當使用流行的62.5/125m多模

11、光纖還有約220米長度的限制。當使用50/125m光纖時，可以增加至約500米。更遠的距離意味著單模光纖的使用。對大廈垂直LAN的所有變動，可能通常與現有的網絡服務平行實施，因此到桌面的服務的中斷可以被保留到極小值。正因為如此，由于網絡服務的中斷對組織成本的影響，可以保持小規模。水平局域網當考慮建筑物內的“水平”分布時，正如“摩爾定律”預測的那樣，我們看到了在數據傳輸速率上同樣的增長，顯示出了近期的加速趨勢，但還是落后垂直數據速率5年。因此，我們希望到2000年能達到1吉比特數據速率和2007年達到10吉比特數據傳輸速率。事實上， 1吉比特網絡接口卡(NIC)現在已經開始進行傳輸；我們開始接受

12、在桌面吉比特網絡的需求之前，它只是時間問題。高帶寬或關鍵比特率應用例如VOIP，視頻流，視頻會議和計算機輔助設計(CAD)，正逐漸變得普遍。不同于建筑物的垂直局域網,水平網絡的升級是非常昂貴。施工總是意味著嚴重擾亂了大樓居住者的正常工作，因此這類活動通常是，有主要的結構性翻新工程時才進行的。在墻壁、地板或天花板上或下面，必須形成空中纜繩。安裝程序必須確保結果并不難看，但也不可避免地破壞了必須有線纜通過的房間的美化價值。提供電源、音頻/數據線纜所采取的處理必須控制在足夠并且美觀程度上。這一切都意味著費用。承包商的成本高。 嚴格地說正是因為這些高費用，于是開發了非屏蔽雙鉸線(UTP)以太網。這將允

13、許在建筑物內使用現有的、低等級的3類電話線纜。為改善這種大眾媒體的帶寬能力已付出了艱苦的努力。但是，一旦確立，隨著這個系統的經濟改善，只得通過重新設計的電纜，這導致在管道中5類，5e類、6類和7類線纜的生產。這些改進已促使10兆，100兆和1吉UTP以太網的發展。事實上,有人說，在鐵絲網上，你接收和發送數據的速率在誤差率接受的范圍內可以達到吉比特位/秒。這只是一個你愿意為編碼器和解碼器支付多少的問題！銅線纜的限制在非常高的數據速率對UTP銅纜布線的使用有內在的局限性。它們是：金屬導體磁化率的屬性的溫度波動。由于從纜繩的輻射，越來越多的信號強度以高數據速率的形式損耗。相對較大的外部串擾影響著弱信

14、號,尤其是在線纜末端附近。數據線纜分享鄰近的包含總線布線的電纜這是極為重要的。在同一線纜中導線對之間的增強信號耦合（串音）。這種情況在它連接硬件的纜繩的末端時被惡化。在連接器上,相對高功率的信號被發射進非常靠近到接收的電纜,沿著電纜長度輻射損失已經開始減弱。這些薄弱接收信號可以從發射器耦合器淹沒不需要的信號。為了克服這些困難，在收發器的硬件設計方面必須投入更多。這些項目的成本將隨著帶寬的增加而增加。現在已經開始開發6類線纜，以便解決其中一些問題，但是，目前，還沒有批準任何標準。除了這些“流動的”方面的銅解決方案,還應該牢記影響他們的選擇的其他因素。或許最重要的是將考慮6類線纜提供的相當低帶寬的

15、改進。網絡帶寬不斷上升的預期將很快超過它，通過把可提供的2.5 Gbs- 1的理論投入使用。這個暫緩的過程很有可能是短的。大約有其互操作性和對現有設施的向后兼容的進一步擔憂。7類線纜目前仍處于研發階段，但在許多業內專家來看，研發是值得的。7類線的最壞預言情況是達到10吉比特速度后暗示著線纜長度限制為大約25m。這必將是一個非常殘酷的限制。所有的改善將是在犧牲更加昂貴的收發器的基礎上。不管結果如何，在更高的數據速率時的距離限制，對于UTP布線來說是很麻煩的。 7類布線，然后，必須至少有一個光纖解決方案？光學技術從另一方面來看，光學技術已經是先進的。擴展帶寬多模光纖和VCSEL激光器的發展已經促使

16、光學技術改進。普通多模光纖的折射率分布并不遵循跨越核心直徑的理想拋物的變化。這些光纖在位于光纖的軸處有一個不連續的小指標,以防止近軸射線被及時有效的傳達。這些是受到最少的色散影響的射線，然而它卻是允許使用高信號率的低等分散。擴展帶寬多模光纖，已經制定了一個改進的折射率分布。他們又提高了在多模光纖上可傳播的吉比特以太網的距離到大約1km。VCSEL激光器有沿光纖中心近軸射線發射的能力，它是使用擴展帶寬光纖的理想助手。傳統上，銅網絡比他們的光學相應物便宜，但是，當數據速率增加時，安裝這些媒介的費用將聚合。這可能發生在2.5 Gbs速率。未來顯然,對未來的所有需求預測是困難重重的,我們必須依賴于過去

17、的經驗。當處理水平網絡時，錯誤判斷將帶來昂貴而持久的后果。但通常只有一個得到正確的機會，因為水平布線的壽命是10年或更多點。通過對比的方式，PC機的壽命約為2 - 3年，而以太交換機3 - 5年。鑒于此,正確的選擇水平布線是至關重要的。對于10Mbs工作，銅3類電纜很足夠了。對于100Mbs工作，銅5類電纜是必需的。對于1 Gbs工作，銅5e類電纜是必需的。對于10 Gbs的工作，延長工作50/125m的光纖電纜是必需的。如果，作為趨向建議，我們也許期待在布線的壽命之內10Gbs的操作，然而，事實上，水平布線是昂貴的改變，我們應該盡我們所能設法使當前的裝置作為所謂“面向未來的”。因為改進的銅纜

18、布線提供的解決方案很可能是短暫的，也很可能和光纖一樣昂貴，所以我們需要在所有的新工作考慮提供光纖。如果因為目前的成本問題，在任何給定的項目并不實際安裝光纖，但至少，在布線內容中應該預留光纖的空間，以適應未來的應用。一種實現這一沒有鋪設任何實際的光纖的方法就是是使用“氣吹光纖”導管。這是一種藉以沿著傳統布線的輸送管道安裝光纖的技術。他們隨后可能會投入使用，通過使用壓縮空氣將光纖吹入預裝管道下到目的地。這具有下列優點：對裝修有最小的干擾；對大廈的員工正常工作模式有最小的干擾。當在零碎的基礎上且和現有的線路同行需要或預算許可時，光纖可以提供額外的帶寬。它允許將開支推遲。氣吹光纖是“原始”（直徑約0.

19、1毫米）的光纖。它是由預安裝管道保護的免受損壞。它比傳統的由熟悉的塑料護套包裝的光纖電纜更便宜。如果環境改變或發生損壞，光纖的等級可以被改變。老化的光纖能夠快速方便地回收,并且被不同的光纖取代。輸送管道是小的，并且可以通過傳統的線纜包含進行運載。損壞的管道可以切去進行修理，并且損壞的部分也可以用新的管替換它。因為光纖具有成熟的優勢技術,大大優于電噪聲免疫、本質電氣安全,優越的帶寬能力,數據高度安全性，通過長距離攜帶數據的能力允許在“主干”的拓撲結構中使用，所以它的用途或潛在的用途應該在所有新線纜施工時認真被考慮。如果歷史告訴我們什么，那就是沒有任何解決方案是“面向未來的”。外文原文：The F

20、uture of Structured Cabling The JHMI Premise Distribution Plan will be consistent with standards specified by the AT&T Premise Distribution System and the International Standards Organization's Integrated Services Digital Network. This includes wallplates, wire for the horizontal distributio

21、n and the voice/data wiring closet modular cross connection equipment.It is recommended that wire runs be less than 230 feet from the voice/data wiring closet to the wall station.Horizontal Distribution Wire & Wallplates AT&T type "D" unshielded twisted pairs shall be used. Each vo

22、ice/data wall station will receive four type "D" cables. Each 4-pair "D" cable will be terminated in an standard RJ45 (8-position) jack so that each wallplate will need to house four RJ-45 jacks.Vertical Distribution Wire & Voice/Data Wiring Closets The wiring closets are gen

23、erally located on each floor of a building.Existing buildings must be evaluated on a case-by-case basis since some of the older buildings have limited space. For new buildings, each closet should be large enough to accommodate a minimum of two standard 19" computer racks. Each of the major prem

24、iseplans recommends mounting electronics in 19" racks. The larger electronic components will require full frame computer racks. These racks will support the ISDN, Ethernet and Token Ring components. In addition, cross connection panels will be required for the telephone wiring, terminal wiring,

25、 Ethernet connections and future Token Ring. Two separate sets of cross connection panels will be required. The data wires will terminate in one set of panels and the voice wires in another.This will segregate functions and minimize confusiondue to two separate organizations maintaining the same set

26、 of wires.The data wires will be patched into the appropriate rack-mounted data hardware (i.e. 3274 controllers, Ethernet Bridge boxes, etc.) and the voice wires will be patched into the rack-mounted voice hardware (where possible). However if needs change, the base wiring plant will be able to supp

27、ort either the voice or the data technology. Modular cross connection equipment provides easier long-termmaintenance and reconfigurability. There are many configurationsavailable from third party sources such as Mod-Tap, Nevada Western and Ortronics. At this point, however, it is most likely that JH

28、MI will go with an AT&T solution. A minimum of two ThickWire Ethernet segments (Belden 9880 or equivalent) will be run through each building to the interconnecting basements. Loops should be left on each floor for future installations.Ethernet cable must have readily available access (i.e. not r

29、un in conduit) to insure future use. A minimum of one 62.5/125 micron fiber riser will be installed in each building riser for future data communications use. Sufficient bulk voice communications riser cable should be run to meet the current and projected requirements. Again, the wiring of existing

30、buildings will need to be evaluated with feasibility in mind. In many buildings the basement wiring closet will act as an intermediate distribution frame back to the main wiring frame. Inter-building linkswill probably be run using fiber optic cable especially to increase the bandwidth of the data c

31、ommunications networks.A Structured Cabling System (SCS) most simply stated is based on following a standard methodology defined by EIA/TIA 568 specifications when planning and installing network cabling for commercial buildings. The purpose of this standard is to specify a generic telecommunication

32、s cabling system for commercial buildings that will support a multi-product, multi-vendor environment. It also provides information that may be used for the design of telecommunications products for commercial enterprises.The EIA/TIA-568 standard includes EIA/TIA-568-B.1 General Requirements,EIA/TIA

33、-568-B.2 Copper Cabling Requirements, EIA/TIA-568-B.3 Fiber Cabling Requirements.Industrial ConsiderationsSo what changes for the industrial environment related to the SCS? Actually very little. All the same standards apply including installation requirements and test requirements. And if you mount

34、everything inside NEMA rated enclosures then nothing changes at all. However if you want to plug into the network from outside the enclosure there is a new connector style available called Industrial RJ45. The specifications are being developed by EIA/TIA and ODV and are nearly complete.Many IT mana

35、gers are unsure of which new technologies to follow. This is partly due to the considerable marketing hype from the manufacturers. The standards bodies are also taking time to ratify category 6 and this is causing uncertainty within the industry.We will be presenting a strategy and method for struct

36、ured cabling that will be the most cost effective solution for today's standards.We will examine:-The Implications for future network design，What is likely to be technically achieved，What will we require in the cabling infrastructure.SummaryThe advantages offered by high specification copper cab

37、ling (category 6 or 7) in data networks are likely to be limited and short lived.In order to avoid serious network disruptions in the future and save costly reworking, "optical fibre to the desktop" deserves serious consideration for new projects. This is also a business critical decision

38、which could impact on your competitiveness. We should do what we can now to ensure our new network installations do not become the legacy networks of the (perhaps none too distant) future.Monotonous Rise in Network Data Rates since the 1980's when network speeds were dictated by the rotor speed

39、of mechanical mechanisms (clunkety-clunk teletypes), the networks have seen a monotonous rise in data rates. The rise has followed "Moore's Law" closely in the past but recently, it has shown evidence of an acceleration faster than that predicted by the law. One-gigabit data rates are

40、available now and 10-gigabit rates are predicted by 2005.Vertical LANIn any building distribution, the "vertical" network carries about 80% of the traffic. This part of a building local area network (LAN) is business critical but fortunately, it is relatively easy to make changes to it. Qu

41、ite often, this part of the network is realised as optical fibre. At one time, the bandwidth offered by optical fibre was regarded as unlimited but that is not the case now. For example, at 1-gigabit rates, there is a length limit of about 220m when using popular 62.5/125µm multi-mode fibre. Th

42、is can be increased to about 500m when using 50/125µm fibre. Greater distances imply the use of monomode fibre. Any changes to the building vertical LAN can usually be made in parallel with the existing network services so disruption of the service to the desktop can be kept to a minimum. Becau

43、se of this, costs to the organisation due to interruption of network service can be kept small.Horizontal LANWhen considering the "horizontal" distribution within a building, we see the same increase in data rates as predicted by "Moore's Law", showing the recent accelerating

44、 trend but lagging the vertical data rates by 5 years. So, we would expect 1-gigabit data rates by year 2000 and 10-gigabit data rates by year 2007. Indeed, 1-gigabit network interface cards (NIC) are being shipped now; it is just a matter of time before we start receiving demands for gigabit n

45、etworking at the desktop. High bandwidth/critical bit rate applications such as VOIP, video streaming, video conferencing and computer aided design (CAD), are becoming common. Unlike the building's vertical LAN, the horizontal network is very costly to upgrade. Installations always mean serious

46、disruption to normal work for a building's occupants, so this sort of activity is normally undertaken when there is a major refurbishment of the fabric. Cableways have to be formed in, on or under walls, floors and ceilings. The installers have to ensure that results are not unsightly but inevit

47、ably there is damage to the amenity value of the rooms through which cables have to pass. Care has to be taken to provide adequate and presentable cable containment for both power and voice/data cables. This all means expense. The cost of ownership is high. It was precisely because of these high cos

48、ts that unshielded twisted pair (UTP) ethernet was developed. This permitted the use of existing, low grade, category 3 telephone cabling within buildings. Strenuous efforts have been made to improve the bandwidth capabilities of this popular medium. However, once firmly established, economic improv

49、ements to this system could be made only by redesign of the cable, leading to the production of category 5, 5e and 6 cables with category 7 in the pipeline. These improvements have enabled the development of 10-megabit, 100-megabit and 1-gigabit ethernet over UTP. Indeed, it has been said that you c

50、an transmit and receive data at gigabit per second rates with acceptable error rates over barbed wire. It's only a matter of how much you are willing to pay for the encoder and decoder!Limitations of Copper CablingThere are intrinsic limitations to the use of UTP copper cabling at very high data

51、 rates. These are:The susceptibility of the metallic conductor's properties to fluctuations in temperature.The increasing loss of signal strength at high data rates due to its radiation from the cable.The relatively large effects of external interference on weak signals, particularly near the en

52、ds of the cable. This is especially important where data cables share adjacent cable containment with mains wiring.The increased signal coupling between pairs of conductors in the same cable (crosstalk).This situation is exacerbated at the ends of the cable where it is attached to the hardware. At t

53、he connector, relatively high power transmit signals are launched into the cable in very close proximity to the receive signals that have already been attenuated by radiation loss along the cable's length. These weak receive signals can be swamped by the unwanted coupled signal from the transmit

54、ter.To overcome these difficulties, more has to be spent in the design of the transceiver hardware. The cost of these items will rise as bandwidth is increased.Category 6 cable has been developed in order to address some of these problems but, at the moment, no standards have been ratified. Apart fr

55、om these "fluid" aspects of copper solutions, there are other factors regarding their choice that should be borne in mind. Perhaps the most important consideration is the rather low bandwidth improvement that category 6 cable will offer. The ever rising expectations of network bandwidth wi

56、ll soon overtake the 2.5 Gbs-1 theoretical through put that it may provide. The respite that it may give is likely to be short. There are further worries about its interoperability and its backward compatibility with existing installations. Category 7 cable is still under development and many expert

57、s in the industry believe the R&D to be worthwhile. Worst case predictions for category 7 at 10-gigabit speeds imply a length restriction of about 25m. This would be a severe limitation. Any improvement will be at the expense of costlier transceivers. In any event, these distance constraints at

58、higher data rates are onerous for UTP cabling. Category 7 then, must be at least a fibre solution?Optical TechnologyOptical technology, on the other hand, is already advanced. It has been improved by the development of extended bandwidth multi-mode fibre and by the development of the VCSEL laser. Th

59、e refractive index profile of ordinary multi-mode fibre does not follow the ideal parabolic variation across the diameter of the core. These fibres have a small index discontinuity located at the axis of the fibre that prevents paraxial rays from being transmitted efficiently. These are the rays that suffer least dispersion and it is low dispersion that permits higher signalling rates to be used. Extended bandwidth multi-mode fibres have been developed with an improved refractive index profile. They have increased the d