新的無線局域網(wǎng)標準

　　計算機專業(yè)英語詞匯指與計算機硬件、軟件、網(wǎng)絡等多方面有關的英語詞匯，主要包括硬件基礎、計算機系統(tǒng)維護、計算機網(wǎng)絡基礎、軟件、程序設計語言、計算機網(wǎng)絡技術、IT職場英語等詞匯。下面是小編為您收集整理的新的無線局域網(wǎng)標準，供大家參考!

　　新的無線局域網(wǎng)標準

　　With portable computers and wireless LANs, users can enjoy greater productivity while away from their desks, whether they are in conference rooms, public areas or remote offices.

　　Until recently, however, wireless LANs were too slow for most enterprise applications.based on the IEEE 802.11 standdrd, they ran at 1M to 2M bit/sec.

　　Now a new high-rate extension to the standard, 802.11b, lets wireless networks support data rates to 11M bit/sec.

　　Ratified in 1997, the original 802.11 standardunited the wireless industury by defining a low-level protocol architecture that worked with conventional upper-layer enterprise protocol stacks. Also, 802.11 maintained compatibility with the three most popular radio transmission types: direct sequence spread spectrum, frequency-hopping spread spectrum, and infrared.

　　Essentially, this new architecture added intelligence at the medium access control(MAC)layer 2 and at the physical(PHY)layer 1, fosteing cooperation between the two layers in performing the critical tasks involved with initiating and maintaining wireless communi-cations.

　　For instance, to ensure reliability of the wireless link, MAC and PHY work together to determine if a clear path exists before they start a transmission.

　　During transmission, they employ special collision-avoidance and arrival-acknowledgment techniques that are not required in wired ethernet LANs.

　　In september 1999, the IEEE approved a new designation, known as 802.11.intended to retain the error-correction，security, powermanagement and other advantages of the original, a key ingredient-a thchnique for increasing bandwidth to 11M bit/sec.

　　Called complementary code keying(CCK)the technique works only in conjunction with the DSSS technology sprcified in the original standard . it does net work with frequency-hopping or infrared transmissions.

　　What CCK does is apply sophisticated mathematical formulas to the DSSS codes, a permitting the code to represent a greater volume of informitter is now able to send multiple bits of information with each DSSS code, enough to make possible the 11M bit /sec in the original standard .

　　The 802.11b standard benefits users by delivering wireless ethernet speeds of 11M bit/sec that can reliably support everyday business applications, e-mail, internet and server network access.

　　With support from the new wireless ethernet from the new wireless ethernet compatibility alliance, founded by 3com, lucent, nokia and several other companies in the wireless LAN business, the new standard will also promise certified interoperability across multivendor platforms.

　　Finally, the 802.11b standard serves as a clamoring for a simplified wireless LAN landscpape.

　　Vendors can now focus on a single, high-speed standard, and users can cut through the clutter of wireless options by fovusing on a standard that delivers multibvendor interoperability and the performance to meet their application needs.

　　有了便攜式和無線局域網(wǎng)，用戶在離開其辦公桌的時候，不管是在會議室、公共區(qū)域還是在遠處辦公室，都能享有更高的生產效率。

　　然而，時至今日，無線局域網(wǎng)對多數(shù)企業(yè)應用來說還是太慢。依據(jù)IEEE802.11標準，他們運行速度為1兆至2兆位/秒。

　　現(xiàn)在對此標準的一個新的更高速擴展，能讓無線網(wǎng)支持高達11兆位/秒的數(shù)據(jù)速率。

　　最初的802.11標準是在1997年提出的，通過定義能與常規(guī)的上層企業(yè)協(xié)議組一起工作的低級協(xié)議體系結構，把無線行業(yè)團結起來了。802.11也保持了與三種最流行的無線電傳輸方式(直接順序擴頻、跳頻擴頻和紅外線)的兼容性。

　　本質上，這種新的體系結構在介質接入控制(MAC)層(第二層)和物理層(第一層)增加了智能，建立這兩層之間在執(zhí)行及開始和保持無線通訊的關鍵任務時的協(xié)作關系。

　　例如：為確保無線連接的可靠性，MAC層和物理層一起工作，以確定在他們開始傳輸之前是否有一條清晰的路徑。

　　在傳輸過程中，他們采用有線以太網(wǎng)不需要的、特殊的避免碰撞和到達應答技術。

　　1999年9月，IEEE批準了稱作802.11B的新名稱，作為802.11的高速擴展。此新的802.11B標準在保留原標準的糾錯、安全、電源管理和其他優(yōu)點的情況下，增加了一項關鍵內容，即把帶寬增加到11兆位/秒的技術。

　　此項技術叫做互補碼鍵控(CCK)，他只與原標準中規(guī)定的直接順序擴頻(DSSS)技術一起工作，不能用跳頻或紅外線傳輸方式工作。

　　CCK所做的工作是把復雜的數(shù)學公式應用于DSSS代碼，以允許該代碼在每個時鐘周期表示更多的信息?，F(xiàn)在發(fā)射機能在每個DSSS代碼中發(fā)送多個信息位，足以實現(xiàn)每秒11兆位/秒的數(shù)據(jù)傳輸率，而不是原標準的2兆位/秒。

　　802.11B 標準給出11兆位/秒的無線以太網(wǎng)速度，給用戶帶來好處，速度能可靠地支持日常的業(yè)務應用、電子郵件、因特網(wǎng)和服務器網(wǎng)絡的接入。

　　由3COM、LUCENT、NOKIA和其他幾家有無線局域網(wǎng)業(yè)務的公司組成的“無線以太網(wǎng)兼容性聯(lián)盟”支持新的標準，此標準也有望實現(xiàn)跨多廠商與用戶團結起來的作用。

　　現(xiàn)在，廠商能專注在單一的高速標準上，用戶也能以通過關注給出廠商互用性和性能。以滿足他們應用要求的標準上，解決了從一大堆無線網(wǎng)中作選擇的難題。

　　目錄允許網(wǎng)絡

　　Almost three years ago, cisco and microsoft annouced the directory enabled network(DEN)initiative, which sought to develop a standard for storing information about network devices, applications and users in a single directory.

　　This directory would bind a user's name and network resource access profile to policies for granting or restricting that access, and delegating bandwidth priorities and privileges.work on standardizing specifications for the directory were handed off to the distributed manage-ment task force (DMTF).

　　In march, the DMTF announced it had completed work on a new version of the common infor-mation model that facilitates the mapping of the CIM schema into a lightweight directory access protocol(LDAP)-compliant directory. CIM defines how to represent network device, system and application data in a directory so it can be easily shared for DEN and enter-prise management purposes.

　　By mapping the CIM schema into an LDAP directory, users will be able to further integrate directory information into an overall enterprise management system, the DMTF says.

　　Customers will make DEN-compliant products a priority once the DMTF makes a little more progress on DEN specifications-such as defining a pollicy schema that would specify data structures for binding directory profiles to network security and quality-of-service (QOS)policies and products soon follow.

　　Perhaps, vendors still have to determine how to use directories to prompt network and applications to configure themselves based on business policies. For example, when a user logs on to a network, the directroy would recognize the user's name, department, location and rank within the company, and bind this information with the user's network access or restriction policies. then the IT infrastructure would configure itself accordingly to enable or disable that a access.

　　One of the killer applications for DEN when it was announced was the ability to link QoS policies to users via dircetories. But bandwidth has become cheaper and more plentiful in the LAN over the past two years, and that's made QOS much less of an issue.

　　Instead of prioritizing bandwidth allocation, users can inexpensively overprovision band-width when they need to support delay-sensitive traffic such as voice and video. Also, simple mechanisms such as setting 802.1p bits on ethernet frame or type-of -service bits in IP headers are enough for LAN QOS.

　　Nonetheless, there 's still a huge demand among enterprise users for directories to enable self-configuring networks based on business policy.

　　DEN for QOS may still apply for WAN applications, edholm says. Indeed cisco has made more strides with DEN in the service provider market than in the enterprise arena.

　　Service providers are looking to DEN to integrate multivendor products into an interoperable operational support system.

　　So despite the silnece, progress on DEN is being the silnece, progress on DEN is being made and activty is expected to pick up once standards become a little more solidiffed.

　　差不多三年前，思科公司和微軟公司宣布了目錄允許網(wǎng)絡(DEN)倡議，該公司要求開發(fā)一個在單一目錄中存儲有關網(wǎng)絡設備、應用程序和用戶等信息的標準。

　　此目錄把用戶的名字和網(wǎng)絡資源訪問簡表與允許或限制訪問的政策和安排帶寬優(yōu)先級別及特權掛起鉤來。此目標標準規(guī)范的研究工作交給了分布管理任務組(DMTF)。

　　今年三月，DETF 宣布完成了新版公共信息模型(CIM)的研究工作，此模型實現(xiàn)了CIM模式映射到簡便目錄訪問協(xié)議(LDAP)的相應目錄中，CIM 定義如何在目錄中表示網(wǎng)絡設備，系統(tǒng)和應用數(shù)據(jù)，因而它很容易為DEN 和企業(yè)管理目的而被共享。

　　DMTF 稱， 通過把CIM 模式映射到LDAP 目錄，用戶就能進一步把目錄信息與整個企業(yè)管理系統(tǒng)結合起來。

　　一旦DMTF在DEN 規(guī)范上取得更多一些進展，如定義一個為把目錄簡表與網(wǎng)絡安全和服務質量(QOS)政策捆綁在一起而規(guī)定數(shù)據(jù)結構的政策模式，以及隨之而來的產品，客戶將優(yōu)先使用符合DEN的產品。

　　廠商們也許還不得不確定怎樣利用目錄來提示網(wǎng)絡和應用程序以便依據(jù)商業(yè)政策來配置他們自己。例如：當一用戶登錄上網(wǎng)時，目錄將會識別出用戶的名字、所在的部門、地點及在公司中的級別，把這些信息與用戶的網(wǎng)絡訪問或限制政策捆綁在一起。然后，IT 基礎設施就能相應地配置自己，以便實現(xiàn)或不讓實現(xiàn)訪問。

　　當年宣布DEN 的最具沖擊力的應用之一是通過目錄把QOS 政策與用戶聯(lián)系起來的能力，但在過去兩年局域網(wǎng)中帶寬變的更為便宜和充足，是QOS不再是個問題。

　　當用戶需要支持對延遲敏感的流量，如聲音和視頻圖象時，他們可以廉價地獲得很大的帶寬，而不用對帶寬進行優(yōu)先等級分配。同時，在以太網(wǎng)楨上設置802.1P 位或者在IP 報頭中設服務類型位等簡單機制對局域網(wǎng)的QOS 來說已經足夠了。

　　然而，在企業(yè)用戶中對目錄還存在著巨大需求，以便能夠依據(jù)商業(yè)政策自行配置網(wǎng)絡。

　　EDHOLM說：“實現(xiàn)QOS 的DEN 還可以應用于廣域網(wǎng)上的應用程序。實際上。思科公司利用DEN 在服務供應商市場上取得了比企業(yè)市場更大的進步。服務供應商正期待著把DEN 做進更多廠商產品中去，成為一個可互用的運行支持系統(tǒng)。

　　盡管(DEN)比較沉默，但DEN 正在取得進步，一旦此標準變的更為穩(wěn)定，DEN 可望會有所作為。