無線局域網(wǎng)的新標(biāo)準(zhǔn)

　　無線局域網(wǎng)是無線電波作為數(shù)據(jù)傳送的媒介，傳送距離一般只有幾十米。接下來小編為大家整理了無線局域網(wǎng)的新標(biāo)準(zhǔn)，希望對你有幫助哦!

　　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 mostpopular 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, apermitting 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(yuǎn)處辦公室，都能享有更高的生產(chǎn)效率。

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

　　現(xiàn)在對此標(biāo)準(zhǔn)的一個新的更高速擴(kuò)展，能讓無線網(wǎng)支持高達(dá)11兆位/秒的數(shù)據(jù)速率。

　　最初的802.11標(biāo)準(zhǔn)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(jié)構(gòu)，把無線行業(yè)團(tuán)結(jié)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(kuò)頻、跳頻擴(kuò)頻和紅外線)的兼容性。

　　本質(zhì)上，這種新的體系結(jié)構(gòu)在介質(zhì)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(guān)鍵任務(wù)時的協(xié)作關(guān)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(dá)應(yīng)答技術(shù)。

　　1999年9月，IEEE批準(zhǔn)了稱作802.11B的新名稱，作為802.11的高速擴(kuò)展。此新的802.11B標(biāo)準(zhǔn)在保留原標(biāo)準(zhǔn)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(guān)鍵內(nèi)容，即把帶寬增加到11兆位/秒的技術(shù)。

　　此項技術(shù)叫做互補碼鍵控(CCK)，他只與原標(biāo)準(zhǔn)中規(guī)定的直接順序擴(kuò)頻(DSSS)技術(shù)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(fù)雜的數(shù)學(xué)公式應(yīng)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(jī)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(biāo)準(zhǔn)的2兆位/秒。

　　802.11B 標(biāo)準(zhǔn)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(wù)應(yīng)用、電子郵件、因特網(wǎng)和服務(wù)器網(wǎng)絡(luò)的接入。

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

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