外文翻譯---無線網(wǎng)絡(luò)在校園中的應(yīng)用

1、<p>　　無線網(wǎng)絡(luò)在校園中的應(yīng)用</p><p>　　一、無線網(wǎng)絡(luò)的概述和IEEE802.11協(xié)議</p><p>　　1．無線局域網(wǎng)（Wireless local－area network，WLAN）概述</p><p>　　所謂無線網(wǎng)絡(luò)，是指無需布線即可實(shí)現(xiàn)計(jì)算機(jī)互連的網(wǎng)絡(luò)。它是無線通信技術(shù)與網(wǎng)絡(luò)技術(shù)相結(jié)合的產(chǎn)物。從專業(yè)角度講，無線局域網(wǎng)就是通過無線

2、信道來實(shí)現(xiàn)網(wǎng)絡(luò)設(shè)備之間的通信，并實(shí)現(xiàn)通信的移動化、個性化和寬帶化。通俗地講，無線局域網(wǎng)就是在不采用網(wǎng)線的情況下，提供以太網(wǎng)互聯(lián)功能。無線網(wǎng)絡(luò)的適用范圍非常廣泛。凡是可以通過布線而建立網(wǎng)絡(luò)的環(huán)境和行業(yè)，無線網(wǎng)絡(luò)也同樣能夠搭建，而通過傳統(tǒng)布線無法解決的環(huán)境或行業(yè)，卻正是無線網(wǎng)絡(luò)大顯身手的地方了。千萬不要以為無線網(wǎng)絡(luò)的保密性太差，恰恰相反，其保密性能比雙絞線要安全得多。</p><p>　　無線網(wǎng)，是采用空氣作傳輸介質(zhì)

3、，用電磁波作為載體來傳輸數(shù)據(jù)，目前無線網(wǎng)聯(lián)網(wǎng)費(fèi)用較高，還不太普及。但由于聯(lián)網(wǎng)方式靈活方便，是一種很有前途的連網(wǎng)方式。</p><p>　　2．無線局域網(wǎng)的配置方式</p><p>　?。?）對等模式。Ad-hoc模式。這種應(yīng)用包含多個無線終端和一個服務(wù)器，均配有無線網(wǎng)卡，但不連接到接入點(diǎn)和有線網(wǎng)絡(luò)，而是通過無線網(wǎng)卡進(jìn)行相互通信。它主要用來在沒有基礎(chǔ)設(shè)施的地方快速而輕松地建無線局域網(wǎng)。 &l

4、t;/p><p>　?。?）基礎(chǔ)結(jié)構(gòu)模式。Infrastructure模式。該模式是目前最常見的一種架構(gòu)，這種架構(gòu)包含一個接入點(diǎn)和多個無線終端，接入點(diǎn)通過電纜連線與有線網(wǎng)絡(luò)連接，通過無線電波與無線終端連接，可以實(shí)現(xiàn)無線終端之間的通信，以及無線終端與有線網(wǎng)絡(luò)之間的通信。通過對這種模式進(jìn)行復(fù)制，可以實(shí)現(xiàn)多個接入點(diǎn)相互連接的更大的無線網(wǎng)絡(luò)。</p><p>　　3.IEEE802.11協(xié)議簡介<

5、;/p><p>　　無線局域網(wǎng)技術(shù)（包括IEEE802.11、藍(lán)牙技術(shù)和HomeRF等）將是新世紀(jì)無線通信領(lǐng)域最有發(fā)展前景的重大技術(shù)之一。以IEEE（電氣和電子工程師協(xié)會）為代表的多個研究機(jī)構(gòu)針對不同的應(yīng)用場合，制定了一系列協(xié)議標(biāo)準(zhǔn)，推動了無線局域網(wǎng)的實(shí)用化。</p><p>　　4．IEEE802.11系列協(xié)議</p><p>　　作為全球公認(rèn)的局域網(wǎng)權(quán)威，IEEE

6、802工作組建立的標(biāo)準(zhǔn)在局域網(wǎng)領(lǐng)域內(nèi)得到了廣泛應(yīng)用。這些協(xié)議包括802.3以太網(wǎng)協(xié)議、802.5令牌環(huán)協(xié)議和802.3z100BASE-T快速以太網(wǎng)協(xié)議等。IEEE于1997年發(fā)布了無線局域網(wǎng)領(lǐng)域第一個在國際上被認(rèn)可的協(xié)議——802.11協(xié)議。1999年9月，IEEE提出802.11b協(xié)議，用于對802.11協(xié)議進(jìn)行補(bǔ)充，之后又推出了802.11a、802.11g等一系列協(xié)議，從而進(jìn)一步完善了無線局域網(wǎng)規(guī)范。IEEE802.11工作組制

7、訂的具體協(xié)議如下：</p><p>　?。?）IEEE802.11a </p><p>　　802.11a采用正交頻分（OFDM）技術(shù)調(diào)制數(shù)據(jù)，使用5GHz的頻帶。OFDM技術(shù)將無線信道分成以低數(shù)據(jù)速率并行傳輸?shù)姆诸l率，然后再將這些頻率一起放回接收端，可提供25Mbit/s的無線ATM接口和10Mbit/s的以太網(wǎng)無線幀結(jié)構(gòu)接口，以及TDD/TDMA的空中接口。在很大程度上可提高傳輸速度，

8、改進(jìn)信號質(zhì)量，克服干擾。物理層速率可達(dá)54Mbit/s，傳輸層可達(dá)25Mbit/s，能滿足室內(nèi)及室外的應(yīng)用。 </p><p>　?。?）IEEE802.11b </p><p>　　802.11b也被稱為Wi-Fi技術(shù)，采用補(bǔ)碼鍵控（CCK）調(diào)制方式，使用2.4GHz頻帶，其對無線局域網(wǎng)通信的最大貢獻(xiàn)是可以支持兩種速率--5.5Mbit/s和11Mbit/s。多速率機(jī)制的介質(zhì)訪問控制可確

9、保當(dāng)工作站之間距離過長或干擾太大、信噪比低于某個門限值時，傳輸速率能夠從11Mbit/s自動降到5.5Mbit/s，或根據(jù)直序擴(kuò)頻技術(shù)調(diào)整到2Mbit/s和1Mbit/s。在不違反FCC規(guī)定的前提下，采用跳頻技術(shù)無法支持更高的速率，因此需要選擇DSSS作為該標(biāo)準(zhǔn)的惟一物理層技術(shù)。 </p><p>　?。?）IEEE802.11g </p><p>　　2001年11月，在802.11 I

10、EEE會議上形成了802.11g標(biāo)準(zhǔn)草案，目的是在2.4GHz頻段實(shí)現(xiàn)802.11a的速率要求。該標(biāo)準(zhǔn)將于2003年初獲得批準(zhǔn)。802.11g采用PBCC或CCK/OFDM調(diào)制方式，使用2.4GHz頻段，對現(xiàn)有的802.11b系統(tǒng)向下兼容。它既能適應(yīng)傳統(tǒng)的802.11b標(biāo)準(zhǔn)(在2.4GHz頻率下提供的數(shù)據(jù)傳輸率為11Mbit/s)，也符合802.11a標(biāo)準(zhǔn)(在5GHz頻率下提供的數(shù)據(jù)傳輸率56Mbit/s)，從而解決了對已有的802.1

11、1b設(shè)備的兼容。用戶還可以配置與802.11a、802.11b以及802.11g均相互兼容的多方式無線局域網(wǎng)，有利于促進(jìn)無線網(wǎng)絡(luò)市場的發(fā)展。</p><p>　　5.目前的幾種無線網(wǎng)絡(luò)技術(shù)</p><p>　　目前，實(shí)現(xiàn)無線網(wǎng)絡(luò)的技術(shù)，有藍(lán)牙無線接入技術(shù)、家庭網(wǎng)絡(luò)的HomeRF以及IEEE802.11連接技術(shù)。</p><p>　　1)藍(lán)牙技術(shù)：Bluetooth

12、（藍(lán)牙）是一種短距的無線通訊技術(shù)，電子裝置彼此可以透過藍(lán)牙而連接起來，傳統(tǒng)的電線在這里就毫無用武之地了。透過芯片上的無線接收器，配有藍(lán)牙技術(shù)的電子產(chǎn)品能夠在十米的距離內(nèi)彼此相通，傳輸速度可以達(dá)到10M/s。以往紅外線接口的傳輸技術(shù)需要電子裝置在視線之內(nèi)的距離，而現(xiàn)在有了藍(lán)牙技術(shù)，這樣的麻煩也可以免除了。不過Bluetooth產(chǎn)品致命的缺陷是任何藍(lán)牙產(chǎn)品都離不開Bluetooth芯片、Bluetooth模塊較難生產(chǎn)，Bluetooth難于

13、全面測試。這三點(diǎn)是藍(lán)牙產(chǎn)品發(fā)展的瓶頸。</p><p>　　2)HomeRF技術(shù)：HomeRF是由HomeRF工作組開發(fā)的，是在家庭區(qū)域范圍內(nèi)的任何地方，在PC機(jī)和用戶電子設(shè)備之間實(shí)現(xiàn)無線數(shù)字通信的開放性工業(yè)標(biāo)準(zhǔn)。作為無線技術(shù)方案，它代替了需要鋪設(shè)昂貴傳輸線的有線家庭網(wǎng)絡(luò)，為網(wǎng)絡(luò)中的設(shè)備，如筆記本電腦和Internet應(yīng)用提供了漫游功能。HomeRF工作頻段是2.4GHz，支持?jǐn)?shù)據(jù)和音頻。該協(xié)議的網(wǎng)絡(luò)是對等網(wǎng)，

14、也就是說，網(wǎng)上的每一個節(jié)點(diǎn)都是西對獨(dú)立的，不受中央節(jié)點(diǎn)的控制。因此，任何一個節(jié)點(diǎn)離開網(wǎng)絡(luò)都不會影響到網(wǎng)絡(luò)上其他節(jié)點(diǎn)的正常工作。它的另外一個特點(diǎn)是低功耗，很適合筆記本電腦。 </p><p>　　3)IEEE802.11 技術(shù)：IEEE802.11是IEEE最初制定的一個無線局域網(wǎng)標(biāo)準(zhǔn)，主要用于解決辦公室局域網(wǎng)和校園網(wǎng)中用戶與用戶終端的無線接入，業(yè)務(wù)主要限于數(shù)據(jù)存取，速率最高只能達(dá)到2Mb/s。</p>

15、;<p>　　由于IEEE802.11在速率和傳輸距離上都不能滿足人們的需要，因此，IEEE小組又相繼推出了IEEE802.11b和IEEE802.11a兩個新標(biāo)準(zhǔn)。三者之間技術(shù)上的主要差別在于MAC子層和物理層。此外還出現(xiàn)了最新802.11g。本文主要討論以802.11b為基礎(chǔ)的無線局域網(wǎng)。</p><p>　　6．無線局域網(wǎng)的優(yōu)勢 </p><p>　　無線局域網(wǎng)的網(wǎng)絡(luò)速

16、度與以太網(wǎng)相當(dāng)，一個AP最多可支持多達(dá)上百個用戶的接入，最大傳輸范圍可達(dá)到幾十公里，具有以下的鮮明特點(diǎn)： </p><p><b>　　1)具有高移動性；</b></p><p>　　通信范圍不受環(huán)境條件的限制，拓寬了網(wǎng)絡(luò)的傳輸范圍。在有線局域中，兩個站點(diǎn)的距離在使用銅纜（粗纜）時被限制在 500m，即使采用單模光纖也只能達(dá)到3000m，而無線局域網(wǎng)中兩個站點(diǎn)間的距離

17、可達(dá)到50km。一般來說，如教室、圖書館、會議室等地方一般是不可能布設(shè)太多信息點(diǎn)的，但是隨著學(xué)生中筆記本電腦的普及和現(xiàn)代化教學(xué)的普及，上述場所往往在同一時刻有大量的電腦，而目前的有線校園網(wǎng)沒有辦法使學(xué)生們在這些區(qū)域上網(wǎng)。采用無線方式，在有限的信息點(diǎn)上連接無線接入器，就可以輕松從一個信息點(diǎn)擴(kuò)展到成百上千個信息點(diǎn)的應(yīng)用。 </p><p>　　2)抗干擾性強(qiáng)、網(wǎng)絡(luò)的保密性好；</p><p>

18、　　對于有線局域網(wǎng)中的諸多安全問題，在無線局域網(wǎng)中基本上可以避免。 </p><p>　　3)建網(wǎng)容易，管理方便；</p><p>　　相對于有線網(wǎng)絡(luò)，無線局域網(wǎng)的組建、配置和維護(hù)較為容易，一般計(jì)算機(jī)工作人員都可以勝任網(wǎng)絡(luò)的管理工作。AP無線接入點(diǎn)可以使原來的一個信息點(diǎn)同時接入數(shù)十乃至數(shù)百個用戶設(shè)備，布線的投資以及維護(hù)成本大大降低。 </p><p><b&g

19、t;　　4)安裝便捷；</b></p><p>　　一般在網(wǎng)絡(luò)建設(shè)中，施工周期最長、對周邊環(huán)境影響最大的，就是網(wǎng)絡(luò)布線施工工程。在施工過程中，往往需要破墻掘地、穿線架管。而WLAN最大的優(yōu)勢就是免去或減少了網(wǎng)絡(luò)布線的工作量，一般只要安裝一個或多個接入點(diǎn) (Access Point)設(shè)備，就可建立覆蓋整個建筑或地區(qū)的局域網(wǎng)絡(luò)。在實(shí)驗(yàn)室、體育館、禮堂等地方是不宜布線的，但校園網(wǎng)的用戶卻有上網(wǎng)的需求，采用無

20、線局域網(wǎng)，可以簡化在這些區(qū)域網(wǎng)絡(luò)實(shí)施，提供直徑近200米的無線網(wǎng)絡(luò)覆蓋，用戶可以在無線所覆蓋的區(qū)域移動應(yīng)用。</p><p><b>　　5）使用靈活；</b></p><p>　　在有線網(wǎng)絡(luò)中，網(wǎng)絡(luò)設(shè)備的安放位置受網(wǎng)絡(luò)信息點(diǎn)位置的限制。而一旦 WLAN建成后，在無線網(wǎng)的信號覆蓋區(qū)域內(nèi)，任何一個位置都可以接入網(wǎng)絡(luò)。提高教學(xué)效率。教師和學(xué)生上課的時候不必再往返于圖書館、

21、辦公室、教室、宿舍，采用無線方案可以使老師和同學(xué)們在上述地方隨意的檢索圖書館的網(wǎng)上資料、服務(wù)器的教案、寢室電腦里的作業(yè)。同時，為用戶對校園網(wǎng)的其他資源的應(yīng)用提供了更便利的條件，提高了資源的利用率。</p><p><b>　　6）易于擴(kuò)展；</b></p><p>　　WLAN有多種配置方式，能夠根據(jù)需要靈活選擇。這樣， WLAN就能勝任從只有幾個用戶的小型局域網(wǎng)到上

22、千用戶的大型網(wǎng)絡(luò)，并且能夠提供像“漫游 (Roaming) ”等有線網(wǎng)絡(luò)無法提供的特性。</p><p>　　7．無線局域網(wǎng)的硬件設(shè)備</p><p>　　無線網(wǎng)絡(luò)的硬件設(shè)備主要包括4種，即無線網(wǎng)卡、無線AP、無線路由和無線天線等。</p><p><b>　?。?）無線網(wǎng)卡</b></p><p>　　無線網(wǎng)卡的作用類

23、似于以太網(wǎng)中的網(wǎng)卡，作為無線網(wǎng)絡(luò)的接口，實(shí)現(xiàn)與無線網(wǎng)絡(luò)的連接。無線網(wǎng)卡根據(jù)接口類型的不同，主要分為三種類型，即PCMCIA無線網(wǎng)卡、PCI無線網(wǎng)卡和USB無線網(wǎng)卡。</p><p>　　PCMCIA無線網(wǎng)卡僅適用于筆記本電腦，支持熱插拔，可以非常方便地實(shí)現(xiàn)移動式無線接入。PCI接口無線網(wǎng)卡適用于普通的臺式計(jì)算機(jī)使用。其實(shí)PCI接口的無線網(wǎng)卡只是在PCI轉(zhuǎn)接卡上插入一塊普通的PC卡。</p><

24、p>　　USB接口無線網(wǎng)卡適用于筆記本電腦和臺式機(jī)，支持熱插撥。不過，由于USB網(wǎng)卡對筆記本而言是個累贅，因此，USB網(wǎng)卡通常被用于臺式機(jī)。</p><p><b>　?。?）無線AP</b></p><p>　　無線接入點(diǎn)或稱無線AP（Access Point），其作用類似于以太網(wǎng)中的集線器。它是用于無線網(wǎng)絡(luò)的無線交換機(jī)，也是無線網(wǎng)絡(luò)的核心。無線AP是移動計(jì)算

25、機(jī)用戶進(jìn)入有線網(wǎng)絡(luò)的接入點(diǎn)，主要用于寬帶家庭、大樓內(nèi)部以及園區(qū)內(nèi)部，典型距離覆蓋幾十米至上百米，目前主要技術(shù)為802.11系列。大多數(shù)無線AP還帶有接入點(diǎn)客戶端模式（AP client），可以和其它AP進(jìn)行無線連接，延展網(wǎng)絡(luò)的覆蓋范圍。</p><p><b>　　（3）無線網(wǎng)橋</b></p><p>　　安裝于室外的無線AP通常稱為無線網(wǎng)橋，主要用于實(shí)現(xiàn)室外的無線

26、漫游、無線網(wǎng)絡(luò)的空中接力，或用于搭建點(diǎn)對點(diǎn)、點(diǎn)對多點(diǎn)的無線連接。</p><p><b>　?。?）無線路由器</b></p><p>　　無線路由器事實(shí)上就是無線AP與寬帶路由器的結(jié)合。借助于無線路由器，可實(shí)現(xiàn)無線網(wǎng)絡(luò)中的Internet連接共享，實(shí)現(xiàn)ADSL、Cable Modem和小區(qū)寬帶的無線共享接入。如果不購置無線路由，就必須在無線網(wǎng)絡(luò)中設(shè)置一臺代理服務(wù)器才

27、可以實(shí)現(xiàn)Internet連接共享。</p><p><b>　?。?）無線天線</b></p><p>　　無線天線有許多種類型，常見的有兩種，一種是室內(nèi)天線，一種是室外天線。室內(nèi)天線主要有兩種，即板狀定向天線和柱狀全向天線。室外天線的類型比較多，常見的也有兩種，即鍋狀定向天線和棒狀全向天線。室外天線的優(yōu)點(diǎn)是傳輸距離遠(yuǎn)。比較適合遠(yuǎn)距離傳輸。 </p>&

28、lt;p>　　二、基于IEEE802.11標(biāo)準(zhǔn)校園無線網(wǎng)絡(luò)的設(shè)計(jì)方案</p><p>　　1．無線局域網(wǎng)絡(luò)優(yōu)勢討論</p><p>　　本設(shè)計(jì)的優(yōu)勢在于減少了樓層間的無線干擾，把跨樓層的漫游任務(wù)交給了放置在相同房間的無線路由器陣列實(shí)現(xiàn)，并且利用了交換機(jī)這種原始有線設(shè)備提高了網(wǎng)絡(luò)的安全性和穩(wěn)定性，布線系統(tǒng)則采用了輕型線與以太網(wǎng)供電系統(tǒng)，增加了網(wǎng)絡(luò)的靈活性，超五類雙絞線的使用，為網(wǎng)絡(luò)的升

29、級和維護(hù)簡便性低價性提供了有力的保障。無線局域網(wǎng)在單純實(shí)現(xiàn)局域網(wǎng)的目標(biāo)時不對交換機(jī)做過多的要求，交換機(jī)僅作為訪問互聯(lián)網(wǎng)絡(luò)的安全設(shè)備，同時將無線路由器作為各個邏輯區(qū)域的交換機(jī)與無線中繼器，利用內(nèi)多種安全機(jī)制的綜合使用，可以有效的保障網(wǎng)絡(luò)的安全要求，設(shè)計(jì)布線可以大量使用現(xiàn)有布線體系，同時冗余下來的設(shè)備可以再為無線局域網(wǎng)所使用，可以以超低的成本對無線局域網(wǎng)絡(luò)進(jìn)行擴(kuò)充，最大限度的保護(hù)了已有投資，該設(shè)計(jì)采用了成熟的主流802.11g54M技術(shù)標(biāo)準(zhǔn)

30、，同時不依賴于具體設(shè)備的網(wǎng)絡(luò)設(shè)計(jì)可以使得無線局域網(wǎng)絡(luò)迅速升級到802.11n108M技術(shù)標(biāo)準(zhǔn)。網(wǎng)絡(luò)易于擴(kuò)展，不同于傳統(tǒng)設(shè)計(jì)的是我們將無線路由器作為小型交換機(jī)來充分保障網(wǎng)絡(luò)的安全性。內(nèi)外網(wǎng)絡(luò)的劃分與電化教學(xué)中心網(wǎng)絡(luò)控制室作為互聯(lián)網(wǎng)絡(luò)唯一的接入點(diǎn)，不但有利于接入用戶的綜合管理，同時對網(wǎng)絡(luò)可以進(jìn)行集中管理，根據(jù)即時</p><p>　　2．無線局域網(wǎng)需求分析</p><p>　　本次無線局域網(wǎng)絡(luò)

31、設(shè)計(jì)，以教學(xué)大樓為設(shè)計(jì)目標(biāo)，模擬建設(shè)一個采用在先進(jìn)技術(shù)的無線局域網(wǎng)絡(luò)，以服務(wù)于學(xué)生機(jī)房的教學(xué)、科研以及其他應(yīng)用。要求無線局域網(wǎng)除了安全穩(wěn)定之外，并且有良好的擴(kuò)展性和自由的移動性，同時要求方案就提供的產(chǎn)品不僅要經(jīng)濟(jì)，而且建成后的網(wǎng)絡(luò)還具有維護(hù)工作少等特點(diǎn)。同時所提供的設(shè)計(jì)方案具有推廣價值，滿足信息化校園網(wǎng)絡(luò)的標(biāo)準(zhǔn)。教學(xué)樓用戶容量為500人規(guī)模，用戶的類型包括學(xué)生、遠(yuǎn)程辦公的管理員、臨時會議辦公人員，有穩(wěn)定組網(wǎng)、遠(yuǎn)程接入與臨時組網(wǎng)的需求,同

32、時無線局域網(wǎng)絡(luò)需要接入教育網(wǎng)絡(luò)與Internet網(wǎng)絡(luò)。</p><p>　　3．無線網(wǎng)絡(luò)技術(shù)的規(guī)劃</p><p>　　本次無線局域網(wǎng)絡(luò)設(shè)計(jì)環(huán)境即是教學(xué)樓的五、六層，共有十間網(wǎng)絡(luò)實(shí)驗(yàn)室，用戶容量為500，同時擁有會議室、主任室、網(wǎng)絡(luò)控制室、值班室，同時要求公共區(qū)域必須有網(wǎng)絡(luò)的覆蓋，基于接入點(diǎn)的帶寬共享機(jī)制，根據(jù)無線網(wǎng)絡(luò)設(shè)計(jì)普遍適用于802.11a及802.11g網(wǎng)絡(luò)的有效經(jīng)驗(yàn)法則，是為每位

33、用戶4Mbps帶寬，可以提供與用戶在有線局域網(wǎng)上相同的使用感受。適用于802.11b網(wǎng)絡(luò)的經(jīng)驗(yàn)法則是為每為用戶分配1Mbps帶寬，這可以提供類似與寬帶ADSL連接類似的用戶使用感受(但11b標(biāo)準(zhǔn)已經(jīng)無法適應(yīng)校園網(wǎng)絡(luò)的應(yīng)用需求，因此本次設(shè)計(jì)主要采用802.11g標(biāo)準(zhǔn))。因此如果要實(shí)現(xiàn)每間教室50人以上同時上網(wǎng)的性能需求，則要為每間教室分配至少200M的帶寬。由于網(wǎng)絡(luò)實(shí)驗(yàn)室用戶密度較大、信號傳輸環(huán)境很差，因此設(shè)計(jì)較小的蜂窩即接入點(diǎn)采用定向天

34、線進(jìn)行無線覆蓋，僅為保證漫游需求在兩房間交界處采用全向天線，接入方式上可以選擇固定臺式計(jì)算機(jī)接入、遠(yuǎn)程接入與移動筆記本接入的方式。每臺路由器大約能帶動的用戶上限為32左右，因此，四臺無線路由器可以充分滿足一間教室50人同時訪問網(wǎng)絡(luò)的需求，將信號功率上適當(dāng)減小，具體數(shù)值需專業(yè)設(shè)備進(jìn)行檢測，</p><p>　　The Application of Wireless Network in The Campus<

35、/p><p>　　One, a wireless network and IEEE802.11 protocols</p><p>　　The 1 Wireless LAN ( Wireless Localarea network, WLAN ) overview</p><p>　　Wireless network without wiring, refers to

36、realize computer interconnection network. It is the wireless communication technology and network technology to combine the product. From a professional point of view, the wireless local area network is through the wirel

37、ess channel to realize the network communication between devices, and the realization of mobile communications, personal and broadband. Popularly speaking, wireless LAN is not in the line of cases, to provide Ethernet in

38、terconnection fun</p><p>　　Wireless network, air is used as the transmission medium, electromagnetic wave as a carrier to transmit data, the wireless networking cost is higher, also not too popular. But beca

39、use the networking mode is flexible and convenient, is a promising networking system.</p><p>　　The 2Wireless LAN configuration</p><p>　　(1) reciprocal mode. Ad-hoc mode. This application contain

40、s a plurality of wireless terminals and a server, are equipped with wireless network card, but not connected to the access point and the cable network, but through wireless network card to communicate with each other. It

41、 is mainly used in the absence of infrastructure in place quickly and easily build wireless local area network.</p><p>　　(2) the infrastructure mode. Infrastructure mode. The pattern is currently one of the

42、most common architecture, this architecture includes an access point and a plurality of wireless terminal, access point via the cable connection and a wired network connection, through radio and wireless terminals are co

43、nnected, can realize the wireless communication between terminals, and the wireless terminal and the cable network communication between. Based on this model to copy, can achieve a number of acc</p><p>　　Bri

44、ef introduction of 3.IEEE802.11 protocol</p><p>　　The technology of wireless local area network ( including IEEE802.11, Bluetooth technology and HomeRF ) will be the new century the field of wireless communi

45、cation the most promising one of the most important technologies. IEEE ( Institute of electrical and Electronics Engineers ) as the representative of a number of research institutes for different applications, developed

46、a series of protocols and standards, promote the wireless LAN utility.</p><p>　　4.IEEE802.11 series protocol</p><p>　　As a globally recognized as the local authority, the group of IEEE 802standa

47、rd in establishment of LAN areas has been widely applied. The protocol includes802.3Ethernet, token ring protocol and802.3z100BASE-T802.5Fast Ethernet protocol. In 1997 IEEE released wireless LAN area the first internati

48、onally recognized protocol -- Protocol 802.11. In 1999September, IEEE proposed802.11b protocol, used for 802.11protocols are added, and then introduced the802.11a,802.11g and a series of agreements, which</p><

49、p>　　(1) IEEE802.11a</p><p>　　802.11a orthogonal frequency division modulation ( OFDM ) technology data, use the 5GHz frequency band. OFDM technology wireless channel into the low data rate parallel transm

50、ission frequency, then the frequencies together back in the receiving end, can provide 25Mbit / s wireless ATM interface and 10Mbit / s Ethernet wireless frame structure interface, and TDD / TDMA air interface. To a larg

51、e extent can improve the transmission speed, improved the signal quality, overcome the interference. Phys</p><p>　　(2) IEEE802.11b</p><p>　　802.11b is also called Wi-Fi technology, using the com

52、plementary code keying ( CCK ) modulation, using 2.4GHz band, the wireless local area network communication is the greatest contribution can support two rate -5.5Mbit / s and 11Mbit / s. Multi rate mechanism of medium ac

53、cess control ensures that when the distance between workstations too long or interference is too large, the SNR is below a certain threshold, the transmission rate from11Mbit / s to 5.5Mbit / s automatically, or based on

54、 direc</p><p>　　(3) IEEE802.11g</p><p>　　In2001November,802.11 IEEE conference formed the draft 802.11g standard, aimed at2.4GHz band802.11a rate requirement. The standard will be at the beginni

55、ng of 2003approved. 802.11g using PBCC or CCK / OFDM modulation mode, using the2.4GHz band, the existing802.11b system compatible. It can adapt to the traditional 802.11b ( in2.4GHz frequency provides data transmission r

56、ate of11Mbit / s ), also in line with the 802.11a standard ( in5GHz frequency provides data transmission rate 56Mbit / s ), so </p><p>　　The 5and present several wireless network technology</p><p&

57、gt;　　At present, the realization of wireless network technology, Bluetooth wireless access technology, the HomeRF and IEEE802.11 connected to the home network technology.</p><p>　　1) the Bluetooth Technology

58、: Bluetooth ( Bluetooth ) is a short distance of wireless communication technology, electronic devices can connect through Bluetooth instead of conventional wires, here is no play. Through the wireless chip receiver with

59、 Bluetooth technology, electronic products can be ten meters away from each other within the same, the speed can reach10M / s. Previous infrared interface transmission technology needs of electronic device in sight dista

60、nce, and now with Bluetooth techn</p><p>　　2) HomeRF: HomeRF by HomeRF working group development, is in a home area anywhere within the range, in the PC machine and the user electronic device between wireles

61、s digital communications open industry standard. As wireless technology scheme, it replaced the need to build costly transmission line wired home networking, network equipment, such as a notebook computer and Internet ap

62、plication provides roaming function. HomeRF working frequency is 2.4GHz, support for data and audio. The network pro</p><p>　　3)IEEE802.11: IEEE802.11IEEE technology originally developed by a wireless LAN st

63、andard, mainly used to solve the office LAN and campus network user and the wireless user terminal access, business is mainly limited to data access, only the highest rate reached 2Mb / s.</p><p>　　As a resu

64、lt of IEEE802.11rate and transmission distance are unable to meet the needs of the people, therefore, IEEE group also launched IEEE802.11b and IEEE802.11a two new standards. Between the three technology is the main diffe

65、rence between MAC layer and physical layer. In addition also appeared in the latest 802.11g. This paper mainly discusses the802.11b based wireless lan.</p><p>　　The 6wireless LAN</p><p>　　The wi

66、reless LAN network speed and Ethernet, a AP can support up to hundreds of user access, the maximum transmission range can reach several tens of kilometers, has the following characteristics:</p><p>　　1) havi

67、ng high mobility;</p><p>　　Communication range is not affected by environmental conditions, to broaden the range of transmission network. In the wired local area, two stations distance in the use of copper (

68、 thick ) was restricted to the 500m, even with a single-mode optical fiber can reach 3000m, and wireless local area network in two inter-site distance can reach50km. In general, such as classrooms, library, conference ro

69、oms and other places it is generally not possible laid too much information at the point, but as a s</p><p>　　2) strong anti-interference, network security;</p><p>　　For wired LAN many security

70、problems in WLAN, basically avoided.</p><p>　　3) easy network-construction, convenient management;</p><p>　　Relative to the cable network, wireless LAN, configuration and maintenance easier, gen

71、eral computer staff can do network management. AP wireless access points can be made the original a point of information at the same time access to dozens and even hundreds of user equipment, wiring investment and mainte

72、nance cost is greatly reduced.</p><p>　　4) easy to install;</p><p>　　Generally in network construction, the construction cycle is the longest, the largest impact on the surrounding environment,

73、is the construction of network cabling project. During the construction process, often need to break through the wall to dig, threading tube frame. WLAN is the biggest advantage of replacing or reducing network wiring wo

74、rk, usually as long as the installation of one or more access points ( Access Point ) equipment, can be established to cover the entire building or area lo</p><p>　　5) the use of flexible;</p><p&g

75、t;　　In a wired network, network equipment placement by network information point position limit. Once the WLAN is completed, in the wireless network signal coverage area, any one location can access network. To improve t

76、he teaching efficiency. The teacher and the students when the class does not need to return to office, library, classrooms, dormitories, using wireless solution can make teachers and students in the local random search l

77、ibrary online information, the server plans, dormitory computer </p><p>　　6) easy to expand;</p><p>　　WLAN have a variety of configurations, can choose according to need to be flexible. In this

78、way, WLAN can do from only a few users of small LAN to thousands of users in large networks, and can provide a" roaming ( Roaming )" and other cable networks can provide properties.</p><p>　　The 7w

79、ireless LAN hardware equipment</p><p>　　Wireless network hardware equipment mainly includes 4 kinds, namely the wireless network card, wireless AP, wireless route and wireless antenna.</p><p>　　

80、(1) the wireless net calorie</p><p>　　The wireless net calorie function similar to a Ethernet card, as the wireless network interface, implementation and the wireless network connection. According to the dif

81、ferent types of wireless network card interface, is mainly divided into three types, namely the PCMCIA wireless network card, wireless PCI net calorie and the wireless USB net calorie.</p><p>　　PCMCIA wirele

82、ss network card is only applicable to notebook computer, supports hot plug and play, can easily achieve the mobile wireless access. PCI interface wireless network card is suitable for ordinary desktop computer using. In

83、fact, the PCI interface wireless card only in the PCI adapter card inserted in an ordinary PC card.</p><p>　　USB interface wireless network card is suitable for a notebook computer and a desktop machine, sup

84、porting hot plug. However, because USB card on the notebook is a burden, therefore, USB card is usually used in desktop.</p><p>　　(2) wireless AP</p><p>　　Wireless access point or wireless AP (

85、Access Point ), similar to its role in Ethernet hub. It is used in wireless network of wireless switches, and wireless core network. Wireless AP mobile computer users access to the cable network access point, mainly for

86、broadband family, the interior of the building and garden, the typical distance covered tens of meters, is currently the main technology for the802.11 series. Most wireless AP with access point client mode ( AP client ),

87、 and other AP wireles</p><p>　　(3) wireless bridge</p><p>　　Installed on the outdoor wireless AP is often referred to as a wireless bridge, mainly used for outdoor wireless roaming, wireless rel

88、ay in the air, or structures used for point-to-point, point-to-multipoint wireless connection.</p><p>　　(4) wireless router</p><p>　　The wireless router is in fact AP wireless and broadband rout

89、er combination. With the help of a wireless router, wireless network Internet connection sharing, to achieve ADSL, Cable Modem and broadband wireless sharing access. If you don't buy wireless routing in a wireless ne

90、twork, it must set up a proxy server to realize the Internet connection sharing.</p><p>　　(5) wireless antenna</p><p>　　Wireless antenna has many types, have two kinds commonly, one is indoor an

91、tenna, an outdoor antenna. Indoor antenna mainly has two kinds, namely the plate-like directional antenna and cylindrical omnidirectional antenna. Outdoor antenna type, common also have two kinds, namely the pot of direc

92、tional antennas and rod-like omnidirectional antenna. Outdoor antenna has the advantages of long distance transmission. More suitable for long distance transmission.</p><p>　　Two, based on the IEEE802.11 sta

93、ndard of campus wireless network design</p><p>　　1wireless local area network advantage discuss</p><p>　　This design has the advantage of reducing the floor of radio interference, cross the floo

94、r in the task to give placed in the same room wireless router array, and use of the switch the original cable equipment to improve network security and stability, a wiring system using light line with Ethernet power supp