綜合布線系統(tǒng)設(shè)計(jì)外文翻譯

1、<p>　　附件1 外文資料翻譯譯文：</p><p><b>　　綜合布線的未來</b></p><p>　　JHMI(約翰斯霍普金斯醫(yī)學(xué)研究所)前提的分配計(jì)劃將與由AT＆T的前提分配制度和國際標(biāo)準(zhǔn)組織的綜合業(yè)務(wù)數(shù)字網(wǎng)指定的標(biāo)準(zhǔn)相一致。這包括護(hù)墻板的水平布線分布，和語音/數(shù)據(jù)配線間交叉連接設(shè)備的模塊化。從靠近長城站的語音/數(shù)據(jù)布線建議線路部署小于230英尺

2、。</p><p>　　水平分布電線和墻面板</p><p>　　AT＆T的“D”類非屏蔽雙絞線應(yīng)被使用。每個(gè)語音/數(shù)據(jù)長城站將達(dá)到四對(duì)“D”類電纜的要求。每4對(duì)" D" 類線纜將被匯聚在一個(gè)標(biāo)準(zhǔn)RJ45 (8位)信息插座，以便使每個(gè)墻面板需要安置四個(gè)RJ-45信息插座。</p><p>　　垂直配電線路和語音/數(shù)據(jù)配線間</p>

3、<p>　　配線間一般都部署在每一層樓。因?yàn)槟承└f的大廈座位有限，根據(jù)具體情況必須對(duì)原有房屋進(jìn)行評(píng)估。對(duì)于新樓宇，每個(gè)小房間應(yīng)該至少可以容納兩個(gè)標(biāo)準(zhǔn)19"機(jī)架。其中每項(xiàng)主要的前提計(jì)劃推薦在19"機(jī)架上安裝電子設(shè)備。較大的電子元器件，需要全幀計(jì)算機(jī)機(jī)架。這些機(jī)架將支持ISDN（綜合業(yè)務(wù)數(shù)字網(wǎng)），以太網(wǎng)和令牌環(huán)組件。此外,交叉連接面板將需要電話線路、終端線路，以太網(wǎng)連接和未來的令牌環(huán)。</p>

4、<p>　　交叉連接的兩個(gè)小組將需要單獨(dú)設(shè)置。數(shù)據(jù)線將端接于其中一組面板，而語音線則在另一塊。由于兩個(gè)分開的組織維護(hù)同一組相同的線纜，這將分離作用并且使混亂減到最小。數(shù)據(jù)線將安裝在適當(dāng)?shù)臋C(jī)架式數(shù)據(jù)硬件（如3274控制器，以太網(wǎng)橋箱等），而語音線（如可能）則將安裝到機(jī)架式語音硬件。但是，如果需求發(fā)生變化，基本接線廠商將能夠支持，無論是語音或數(shù)據(jù)的技術(shù)。</p><p>　　模塊化的交叉連接設(shè)備提供長期的維

5、護(hù)和可重構(gòu)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(chuàng)利的第三方資源獲得。在這一點(diǎn)上，然而，很有可能是JHMI要和AT&T使用同一個(gè)解決方案。</p><p>　　每棟建筑到互連的地下室至少兩根粗纜以太網(wǎng)段(貝爾登9880或同等材質(zhì))才能貫穿。線圈應(yīng)該留待日后安裝在每個(gè)樓層。以太網(wǎng)電纜必須有隨時(shí)可用的訪問（即不是在管道運(yùn)行），以確保日后使用。&

6、lt;/p><p>　　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(shù)據(jù)通信使用。充分批量的語音通信電纜冒口應(yīng)該被部署，以滿足當(dāng)前和預(yù)計(jì)的需求。再次，現(xiàn)有建筑物的布線將需要考慮到可行性評(píng)估。在許多建筑物的地下室配線間將作為一個(gè)中間配線架回到主配線架。建筑物間互連可能會(huì)依靠光纜，尤其可以增加數(shù)據(jù)通信網(wǎng)絡(luò)的帶寬。</p><p>　　結(jié)構(gòu)化布線系統(tǒng)(SCS）最簡單地說就是，在安

7、裝時(shí)基于遵循EIA / TIA 568規(guī)范定義的標(biāo)準(zhǔn)，網(wǎng)絡(luò)規(guī)劃和商業(yè)建筑布線方法。本標(biāo)準(zhǔn)的目的是指定一個(gè)通用的、能夠支持多產(chǎn)品，多廠商環(huán)境的商業(yè)建筑物電信布線系統(tǒng)。它還提供了一些可以用來為商業(yè)企業(yè)設(shè)計(jì)通訊產(chǎn)品的信息。</p><p>　　在EIA/TIA-568標(biāo)準(zhǔn)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。</p>

8、<p><b>　　工業(yè)思考</b></p><p>　　還有什么能夠改變與結(jié)構(gòu)化布線系統(tǒng)相關(guān)的工業(yè)環(huán)境嗎?</p><p>　　其實(shí)很少。包括安裝要求和測(cè)試要求適用標(biāo)準(zhǔn)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(xié)會(huì)額定的范圍內(nèi)，那么什么都不需要變的。不過，如果你想從機(jī)箱外面進(jìn)入網(wǎng)絡(luò)，那么有一個(gè)新的連接方式稱為工業(yè)RJ45。這些規(guī)范由EIA/T

9、IA和ODV（開放是數(shù)字視頻）開發(fā)并且是幾乎已經(jīng)完成。</p><p>　　許多IT經(jīng)理感到不太確定應(yīng)該跟隨哪些新的技術(shù)。這部分歸結(jié)于制造商的可觀的營銷炒作。規(guī)范體也需要時(shí)間批準(zhǔn)6類線，因此導(dǎo)致在產(chǎn)業(yè)之內(nèi)的不確定性。</p><p>　　我們將提出一種戰(zhàn)略和結(jié)構(gòu)化布線，這將是當(dāng)今標(biāo)準(zhǔn)的最具成本效益的解決方案。</p><p><b>　　我們將會(huì)研究：&l

10、t;/b></p><p>　　未來網(wǎng)絡(luò)設(shè)計(jì)的影響；</p><p>　　什么將會(huì)有可能在技術(shù)上實(shí)現(xiàn)；</p><p>　　在布線基礎(chǔ)設(shè)施中我們需要什么。</p><p><b>　　總結(jié)</b></p><p>　　高規(guī)格的銅布線在數(shù)據(jù)網(wǎng)絡(luò)（6或7類）中所提供的好處很可能是有限的，短暫的。

11、</p><p>　　為了避免今后嚴(yán)重的網(wǎng)絡(luò)中斷，節(jié)省昂貴的返工，“光纖到桌面”是值得認(rèn)真考慮的新項(xiàng)目。這也可能是對(duì)您競爭性沖擊的企業(yè)重要決定。我們現(xiàn)在應(yīng)該做什么，可以保證我們新的網(wǎng)絡(luò)設(shè)施不會(huì)成為未來(或許一點(diǎn)也不遙遠(yuǎn))的傳統(tǒng)網(wǎng)絡(luò)。</p><p><b>　　網(wǎng)絡(luò)的單調(diào)上升</b></p><p>　　1980年以來的數(shù)據(jù)傳輸速率，當(dāng)網(wǎng)絡(luò)速度

12、被由（clunkety -彈響電傳打字機(jī)）機(jī)械轉(zhuǎn)速機(jī)制決定時(shí)，網(wǎng)絡(luò)已經(jīng)看到了數(shù)據(jù)傳輸速率的單調(diào)上升。在過去，上升趨勢(shì)始終密切遵循“摩爾定律”，但最近，它提供的證據(jù)表明速度加速快于由定律預(yù)測(cè)的。一吉比特?cái)?shù)據(jù)速率現(xiàn)在是可利用的，然而到2005年它預(yù)計(jì)達(dá)到10吉比特。</p><p>　　在任何建筑物分布中，“垂直”網(wǎng)絡(luò)運(yùn)行約80％的流量。這種建筑物局部區(qū)域網(wǎng)絡(luò)（LAN）是關(guān)鍵業(yè)務(wù)的一部分，但是幸運(yùn)地，它是相對(duì)地容易對(duì)

13、它做變動(dòng)的。很多時(shí)候，這個(gè)網(wǎng)絡(luò)的一部分，是用光纖實(shí)現(xiàn)的。有一段時(shí)間，通過光纖提供的帶寬，被認(rèn)為是無限的，但事實(shí)并非這樣。例如，在1吉比特速度時(shí)，當(dāng)使用流行的62.5/125μm多模光纖還有約220米長度的限制。當(dāng)使用50/125μm光纖時(shí)，可以增加至約500米。更遠(yuǎn)的距離意味著單模光纖的使用。對(duì)大廈垂直LAN的所有變動(dòng)，可能通常與現(xiàn)有的網(wǎng)絡(luò)服務(wù)平行實(shí)施，因此到桌面的服務(wù)的中斷可以被保留到極小值。正因?yàn)槿绱?，由于網(wǎng)絡(luò)服務(wù)的中斷對(duì)組織成本的

14、影響，可以保持小規(guī)模。</p><p><b>　　水平局域網(wǎng)</b></p><p>　　當(dāng)考慮建筑物內(nèi)的“水平”分布時(shí)，正如“摩爾定律”預(yù)測(cè)的那樣，我們看到了在數(shù)據(jù)傳輸速率上同樣的增長，顯示出了近期的加速趨勢(shì)，但還是落后垂直數(shù)據(jù)速率5年。</p><p>　　因此，我們希望到2000年能達(dá)到1吉比特?cái)?shù)據(jù)速率和2007年達(dá)到10吉比特?cái)?shù)據(jù)傳輸

15、速率。事實(shí)上， 1吉比特網(wǎng)絡(luò)接口卡(NIC)現(xiàn)在已經(jīng)開始進(jìn)行傳輸；我們開始接受在桌面吉比特網(wǎng)絡(luò)的需求之前，它只是時(shí)間問題。高帶寬或關(guān)鍵比特率應(yīng)用例如VOIP，視頻流，視頻會(huì)議和計(jì)算機(jī)輔助設(shè)計(jì)(CAD)，正逐漸變得普遍。不同于建筑物的垂直局域網(wǎng),水平網(wǎng)絡(luò)的升級(jí)是非常昂貴。施工總是意味著嚴(yán)重?cái)_亂了大樓居住者的正常工作，因此這類活動(dòng)通常是，有主要的結(jié)構(gòu)性翻新工程時(shí)才進(jìn)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(jié)果并

16、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(jià)值。提供電源、音頻/數(shù)據(jù)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(fèi)用。承包商的成本高。 嚴(yán)格地說正是因?yàn)檫@些高費(fèi)用，于是開發(fā)了非屏蔽雙鉸線(UTP)以太網(wǎng)。這將允許在建筑物內(nèi)使用現(xiàn)有的、低等級(jí)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(gè)系統(tǒng)的經(jīng)濟(jì)改善，只得通過重新設(shè)計(jì)的電纜，這導(dǎo)致在管道中5類，5e類、6類和7類線纜的

17、生產(chǎn)。這些改進(jìn)已促使10兆，100兆和</p><p><b>　　銅線纜的限制</b></p><p>　　在非常高的數(shù)據(jù)速率對(duì)UTP銅纜布線的使用有內(nèi)在的局限性。它們是：</p><p>　　金屬導(dǎo)體磁化率的屬性的溫度波動(dòng)。由于從纜繩的輻射，越來越多的信號(hào)強(qiáng)度以高數(shù)據(jù)速率的形式損耗。</p><p>　　相對(duì)較大的外

18、部串?dāng)_影響著弱信號(hào),尤其是在線纜末端附近。數(shù)據(jù)線纜分享鄰近的包含總線布線的電纜這是極為重要的。</p><p>　　在同一線纜中導(dǎo)線對(duì)之間的增強(qiáng)信號(hào)耦合（串音）。</p><p>　　這種情況在它連接硬件的纜繩的末端時(shí)被惡化。在連接器上,相對(duì)高功率的信號(hào)被發(fā)射進(jìn)非?？拷浇邮盏碾娎|,沿著電纜長度輻射損失已經(jīng)開始減弱。這些薄弱接收信號(hào)可以從發(fā)射器耦合器淹沒不需要的信號(hào)。</p>

19、<p>　　為了克服這些困難，在收發(fā)器的硬件設(shè)計(jì)方面必須投入更多。這些項(xiàng)目的成本將隨著帶寬的增加而增加。</p><p>　　現(xiàn)在已經(jīng)開始開發(fā)6類線纜，以便解決其中一些問題，但是，目前，還沒有批準(zhǔn)任何標(biāo)準(zhǔn)。除了這些“流動(dòng)的”方面的銅解決方案,還應(yīng)該牢記影響他們的選擇的其他因素?；蛟S最重要的是將考慮6類線纜提供的相當(dāng)?shù)蛶挼母倪M(jìn)。網(wǎng)絡(luò)帶寬不斷上升的預(yù)期將很快超過它，通過把可提供的2.5 Gbs- 1的理

20、論投入使用。這個(gè)暫緩的過程很有可能是短的。大約有其互操作性和對(duì)現(xiàn)有設(shè)施的向后兼容的進(jìn)一步擔(dān)憂。7類線纜目前仍處于研發(fā)階段，但在許多業(yè)內(nèi)專家來看，研發(fā)是值得的。7類線的最壞預(yù)言情況是達(dá)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(gè)非常殘酷的限制。所有的改善將是在犧牲更加昂貴的收發(fā)器的基礎(chǔ)上。不管結(jié)果如何，在更高的數(shù)據(jù)速率時(shí)的距離限制，對(duì)于UTP布線來說是很麻煩的。 7類布線，然后，必須至少有一個(gè)光纖解決方案？</p&

21、gt;<p><b>　　光學(xué)技術(shù)</b></p><p>　　從另一方面來看，光學(xué)技術(shù)已經(jīng)是先進(jìn)的。擴(kuò)展帶寬多模光纖和VCSEL激光器的發(fā)展已經(jīng)促使光學(xué)技術(shù)改進(jìn)。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(gè)不連續(xù)的小指標(biāo),以防止近軸射線被及時(shí)有效的傳達(dá)。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(hào)率的低等分散。擴(kuò)展帶

22、寬多模光纖，已經(jīng)制定了一個(gè)改進(jìn)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(wǎng)的距離到大約1km。VCSEL激光器有沿光纖中心近軸射線發(fā)射的能力，它是使用擴(kuò)展帶寬光纖的理想助手。</p><p>　　傳統(tǒng)上，銅網(wǎng)絡(luò)比他們的光學(xué)相應(yīng)物便宜，但是，當(dāng)數(shù)據(jù)速率增加時(shí)，安裝這些媒介的費(fèi)用將聚合。這可能發(fā)生在2.5 Gbs速率。</p><p><b>　　未來</b>

23、;</p><p>　　顯然,對(duì)未來的所有需求預(yù)測(cè)是困難重重的,我們必須依賴于過去的經(jīng)驗(yàn)。當(dāng)處理水平網(wǎng)絡(luò)時(shí)，錯(cuò)誤判斷將帶來昂貴而持久的后果。但通常只有一個(gè)得到正確的機(jī)會(huì)，因?yàn)樗讲季€的壽命是10年或更多點(diǎn)。通過對(duì)比的方式，PC機(jī)的壽命約為2 - 3年，而以太交換機(jī)3 - 5年。鑒于此,正確的選擇水平布線是至關(guān)重要的。</p><p>　　對(duì)于10Mbs工作，銅3類電纜很足夠了。</p

24、><p>　　對(duì)于100Mbs工作，銅5類電纜是必需的。</p><p>　　對(duì)于1 Gbs工作，銅5e類電纜是必需的。</p><p>　　對(duì)于10 Gbs的工作，延長工作50/125μm的光纖電纜是必需的。</p><p>　　如果，作為趨向建議，我們也許期待在布線的壽命之內(nèi)10Gbs的操作，然而，事實(shí)上，水平布線是昂貴的改變，我們應(yīng)該盡我們

25、所能設(shè)法使當(dāng)前的裝置作為所謂“面向未來的”。因?yàn)楦倪M(jìn)的銅纜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?yàn)槟壳暗某杀締栴}，在任何給定的項(xiàng)目并不實(shí)際安裝光纖，但至少，在布線內(nèi)容中應(yīng)該預(yù)留光纖的空間，以適應(yīng)未來的應(yīng)用。一種實(shí)現(xiàn)這一沒有鋪設(shè)任何實(shí)際的光纖的方法就是是使用“氣吹光纖”導(dǎo)管。這是一種藉以沿著傳統(tǒng)布線的輸送管道安裝光纖的技術(shù)。他們隨后可能會(huì)投入使用，通過使用壓縮空氣將光纖吹入

26、預(yù)裝管道下到目的地。這具有下列優(yōu)點(diǎn)：</p><p>　　對(duì)裝修有最小的干擾；</p><p>　　對(duì)大廈的員工正常工作模式有最小的干擾。當(dāng)在零碎的基礎(chǔ)上且和現(xiàn)有的線路同行需要或預(yù)算許可時(shí)，光纖可以提供額外的帶寬。它允許將開支推遲。</p><p>　　氣吹光纖是“原始”（直徑約0.1毫米）的光纖。它是由預(yù)安裝管道保護(hù)的免受損壞。它比傳統(tǒng)的由熟悉的塑料護(hù)套包裝的光纖

27、電纜更便宜。</p><p>　　如果環(huán)境改變或發(fā)生損壞，光纖的等級(jí)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。</p><p>　　輸送管道是小的，并且可以通過傳統(tǒng)的線纜包含進(jìn)行運(yùn)載。損壞的管道可以切去進(jìn)行修理，并且損壞的部分也可以用新的管替換它。</p><p>　　因?yàn)楣饫w具有成熟的優(yōu)勢(shì)技術(shù),大大優(yōu)于電噪聲免疫、本質(zhì)電氣安全,優(yōu)越的帶寬能力

28、,數(shù)據(jù)高度安全性，通過長距離攜帶數(shù)據(jù)的能力允許在“主干”的拓?fù)浣Y(jié)構(gòu)中使用，所以它的用途或潛在的用途應(yīng)該在所有新線纜施工時(shí)認(rèn)真被考慮。</p><p>　　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”。</p><p><b>　　外文原文：</b></p><p>　　The Future of Structured Cabli

29、ng</p><p>　　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 D

30、igital Network. This includes wallplates, wire for the horizontal distribution and the voice/data wiring closet modular cross connection equipment.It is recommended that wire runs be less than 230 feet from the voice/dat

31、a wiring closet to the wall station.</p><p>　　Horizontal Distribution Wire & Wallplates</p><p>　　AT&T type "D" unshielded twisted pairs shall be used. Each voice/data wall stat

32、ion 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.</p><p>　　

33、Vertical Distribution Wire & Voice/Data Wiring Closets</p><p>　　The wiring closets are generally located on each floor of a building.Existing buildings must be evaluated on a case-by-case basis since som

34、e 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 premiseplans recommends mounting ele

35、ctronics in 19" racks. The larger electronic components will require full frame computer racks. These racks will support the ISDN, Ethernet and To</p><p>　　Two separate sets of cross connection panels w

36、ill 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 of wires.T

37、he 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)

38、. However if n</p><p>　　Modular cross connection equipment provides easier long-term</p><p>　　maintenance and reconfigurability. There are many configurations</p><p>　　available fro

39、m third party sources such as Mod-Tap, Nevada Western and Ortronics. At this point, however, it is most likely that JHMI will go with an AT&T solution.</p><p>　　A minimum of two ThickWire Ethernet segmen

40、ts (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

41、un in conduit) to insure future use.</p><p>　　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 ri

42、ser cable should be run to meet the current and projected requirements. Again, the wiring of existing buildings will need to be evaluated with feasibility in mind. In many buildings the basement wiring closet will act as

43、 an intermediate distribution frame back to the main wiring frame. Inter-building linkswill probably be run using fiber</p><p>　　A Structured Cabling System (SCS) most simply stated is based on following a s

44、tandard 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 telecommunications cabling system for

45、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.</p><p&g

46、t;　　The EIA/TIA-568 standard includes EIA/TIA-568-B.1 General Requirements,EIA/TIA-568-B.2 Copper Cabling Requirements, EIA/TIA-568-B.3 Fiber Cabling Requirements.</p><p>　　Industrial Considerations</p>

47、;<p>　　So what changes for the industrial environment related to the SCS? </p><p>　　Actually very little. All the same standards apply including installation requirements and test requirements. And if

48、 you mount 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

49、 specifications are being developed by EIA/TIA and ODV and are nearly complete.</p><p>　　Many IT managers are unsure of which new technologies to follow. This is partly due to the considerable marketing hype

50、 from the manufacturers. The standards bodies are also taking time to ratify category 6 and this is causing uncertainty within the industry.</p><p>　　We will be presenting a strategy and method for structure

51、d cabling that will be the most cost effective solution for today's standards.</p><p>　　We will examine:-</p><p>　　The Implications for future network design，</p><p>　　What is l

52、ikely to be technically achieved，</p><p>　　What will we require in the cabling infrastructure.</p><p><b>　　Summary</b></p><p>　　The advantages offered by high specificat

53、ion copper cabling (category 6 or 7) in data networks are likely to be limited and short lived.</p><p>　　In order to avoid serious network disruptions in the future and save costly reworking, "optical f

54、ibre to the desktop" deserves serious consideration for new projects. This is also a business critical decision which could impact on your competitiveness. We should do what we can now to ensure our new network inst

55、allations do not become the legacy networks of the (perhaps none too distant) future.</p><p>　　Monotonous Rise in Network </p><p>　　Data Rates since the 1980's when network speeds were dicta

56、ted by the rotor speed 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 h

57、as shown evidence of an acceleration faster than that predicted by the law. One-gigabit data rates are available now and 10-gigabit rates are predicted by 2005.</p><p>　　Vertical LAN</p><p>　　In

58、 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

59、to it. Quite 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, ther

60、e is a length limit of about 220m when using popular 62.5/125µm mult</p><p>　　Horizontal LAN</p><p>　　When considering the "horizontal" distribution within a building, we see the

61、same increase in data rates as predicted by "Moore's Law", showing the recent accelerating trend but lagging the vertical data rates by 5 years. </p><p>　　So, we would expect 1-gigabit dat

62、a 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 networking at

63、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 ne

64、twork is very costly to upgrade</p><p>　　Limitations of Copper Cabling</p><p>　　There are intrinsic limitations to the use of UTP copper cabling at very high data rates. These are:</p>&l

65、t;p>　　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.</p><p>　　T

66、he relatively large effects of external interference on weak signals, particularly near the ends of the cable. This is especially important where data cables share adjacent cable containment with mains wiring.</p>

67、<p>　　The increased signal coupling between pairs of conductors in the same cable (crosstalk).</p><p>　　This situation is exacerbated at the ends of the cable where it is attached to the hardware. At t

68、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

69、 receive signals can be swamped by the unwanted coupled signal from the transmitter.</p><p>　　To overcome these difficulties, more has to be spent in the design of the transceiver hardware. The cost of these

70、 items will rise as bandwidth is increased.</p><p>　　Category 6 cable has been developed in order to address some of these problems but, at the moment, no standards have been ratified. Apart from these "

71、;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 cabl

72、e will offer. The ever rising expectations of network bandwidth will soon overtake the 2.5 Gbs-1 theoretical through put that it may pro</p><p>　　Optical Technology</p><p>　　Optical technology,

73、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. The refractive index profile of ordinary multi-mode fibre

74、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

75、. These are the rays that suffer least d</p><p>　　Traditionally, copper networks have been cheaper than their optical counterparts, but as data rates increase, the costs of installing these media will conver

76、ge. This is likely to happen at rates of about 2.5 Gbs.</p><p>　　The Future</p><p>　　Obviously, all predictions about future requirements are fraught with difficulty and we must rely heavily on

77、past experience. Errors of judgement when dealing with the horizontal networking are expensive and have long lasting consequences. There is usually only one chance to get it right as the lifetime for horizontal wiring is

78、 10 years or more. By way of contrast, the lifetime of a p.c. is about 2 - 3 years and that of an ether switch 3 - 5 years. In view of this, it is crucial that the right c</p><p>　　For 10 Mbs working, copper

79、 category 3 cabling is quite adequate.</p><p>　　For 100 Mbs working, copper category 5 cabling is required.</p><p>　　For 1 Gbs working, copper category 5e cabling is required.</p><p&g

80、t;　　For 10 Gbs working, extended working 50/125µm fibre optic cabling is required</p><p>　　If, as trends suggest, we may expect 10 Gbs operation within the lifetime of the wiring and in view of the fact

81、 that horizontal wiring is expensive to alter, we should try to make any current installation as so called "future-proof" as we can. As the solution offered by improved copper cabling is likely to be transient

82、and is likely to be just as expensive as fibre, we need to consider the provision of fibre for all new work. If, because of current cost, fibre is not actually installed in any gi</p><p>　　There is minimal d

83、isturbance to decoration.</p><p>　　There is minimal disruption to the normal working patterns of the building's staff. The extra bandwidth that fibre offers can be provided on a piecemeal basis and in pa

84、rallel with existing wiring when need or budget permits. It allows expenditure to be deferred.</p><p>　　Blown fibre is "raw" fibre (about 0.1mm diameter). It is protected from damage by the pre-ins

85、talled conduits. It is cheaper than traditional fibre cable where fibres are encased in the familiar plastic sheath.</p><p>　　The grade of fibre can be changed if circumstances change or if damage occurs. Ol

86、d fibres can be quickly and easily withdrawn and replaced by different ones.</p><p>　　Conduits are small and can be carried by traditional cable containment. Damaged conduit can be repaired by cutting out an

87、d the damaged section and replacing it with new tube.</p><p>　　As fibre has all the advantages of proven technology, far superior immunity to electrical noise, intrinsic electrical safety, superior bandwidth

88、 capability, a high degree of data security and the ability to carry signals over long distances permitting the use of "collapsed backbone" topologies, its use or potential use ought to be seriously considered