無線局域網的新標準
無線局域網是無線電波作爲數據傳送的媒介，傳送距離一般只有幾十米。接下來小編爲大家整理了無線局域網的新標準，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 d 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 nded 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，用戶在離開其辦公桌的時候，不管是在會議室、公共區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，無線局域網對多數企業應用來說還是太慢。依據IEEE802.11標準，他們運行速度爲1兆至2兆位/秒。
現在對此標準的一個新的更高速擴展，能讓無線網支持高達11兆位/秒的數據速率。
最初的802.11標準是在1997年提出的，通過定義能與常規的上層企業協議組一起工作的低級協議體系結構，把無線行業團結起來了。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行及開始和保持無線通訊的關鍵任務時的協作關係。
例如：爲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，他們採用有線以太網不需要的、特殊的避免碰撞和到達應答技術。
1999年9月，IEEE批准了稱作802.11B的新名稱，作爲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所做的工作是把複雜的數學公式應用於DSSS代碼，以允許該代碼在每個時鐘週期表示更多的信息。現在發射機能在每個DSSS代碼中發送多個信息位，足以實現每秒11兆位/秒的數據傳輸率，而不是原標準的2兆位/秒。
802.11B 標準給出11兆位/秒的無線以太網速度，給用戶帶來好處，速度能可靠地支持日常的業務應用、電子郵件、因特網和服務器網絡的接入。
由3COM、LUCENT、NOKIA和其他幾家有無線局域網業務的公司組成的“無線以太網兼容性聯盟”支持新的標準，此標準也有望實現跨多廠商與用戶團結起來的作用。
現在，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中作選擇的難題。
