電子與通信工程專業(yè)英語Unit12WirelessLANTechnologyHowever,thismotivationforwirelessLANswasovertakenbyevents.First,asawarenessoftheneedforLANsbecamegreater,architectsdesignednewbuildingstoincludeextensiveprewiringfordataapplications.Second,withadvancesindatatransmissiontechnology,thereisanincreasingrelianceontwistedpaircablingforLANsand,inparticular,Category3andCategory5unshieldedtwistedpair.MostolderbuildingarealreadywiredwithanabundanceofCategory3cable,andmanynewerbuildingsareprewiredwithCategory5.Thus,theuseofawirelessLANtoreplacewiredLANshasnothappenedtoanygreatextent.However,inanumberofenvironments,thereisaroleforthewirelessLANasanalternativetoawiredLAN.Examplesincludebuildingswithlargeopenareas,suchasmanufacturingplants,stockexchangetradingfloors,andwarehouses;historicalbuildingswithinsufficienttwistedpairandwheredrillingholesfornewwiringisprohibited,andsmallofficeswhereinstallationandmaintenanceofwiredLANsisnoteconomical.Inallofthesecases,awirelessLANprovidesaneffectiveandmoreattractivealternative.Inmostofthesecases,anorganizationwillalsohaveawiredLANtosupportserversandsomestationaryworkstations.Forexample,amanufacturingfacilitytypicallyhasanofficeareathatisseparatefromthefactoryfloorbutthatmustbelinkedtoitfornetworkingpurposes[2].Therefore,typically,awirelessLANwillbelinkedintoawiredLANonthesamepremises.Thus,thisapplicationareaisreferredtoasLANextension.Fig

12.1indicatesasimplewirelessLANconfigurationthatistypicalofmanyenvironments[3].ThereisabackbonewiredLAN,suchasEthernet,thatsupportsservers,workstations,andoneormorebridgesorrouterstolinkwithothernetworks.Inaddition,thereisacontrolmodule(CM)thatactsasaninterfacetoawirelessLAN.ThecontrolmoduleincludeseitherbridgeorrouterfunctionalitytolinkthewirelessLANtothebackbone.Itincludessomesortofaccesscontrollogic,suchasapollingortokenpassingscheme,toregulatetheaccessfromtheendsystems.Notethatsomeoftheendsystemsarestandalonedevices,suchasaworkstationoraserver.Hubsorotherusermodules(UMs)thatcontrolanumberofstationsofawiredLANmayalsobepartofthewirelessLANconfiguration.

Fig12.1ExamplesinglecellwirelessLANconfigurationTheconfigurationofFig12.1canbereferredtoasasinglecellwirelessLAN[4],allofthewirelessendsystemsarewithinrangeofasinglecontrolmodule.Anothercommonconfiguration,suggestedbyFig12.2,isamultiplecellwirelessLAN.Inthiscase,therearecontrolmultiplecontrolmodulesinterconnectedbyawiredLAN.Eachcontrolmodulesupportsanumberofwirelessendsystemswithinitstransmissionrange.Forexample,withaninfraredLAN,transmissionislimitedtoasingleroom;therefore,onecellisneededforeachroominanofficebuildingthatrequireswirelesssupport.

2)

CrossBuildingInterconnect

AnotheruseofwirelessLANtechnologyistoconnectLANsinnearbybuildings,bethewiredorwirelessLANs[5].Inthiscase,apointtopointwirelesslinkisusedbetweentwobuildings.Thedevicessoconnectedaretypicallybridgesorrouters.ThissinglepointtopointlinkisnotaLANperse,butitisusualtoincludethisapplicationundertheheadingofwirelessLAN.

Fig12.2ExamplemultiplecellwirelessLANconfiguration3)

NomadicAccess

NomadicaccessprovidesawirelesslinkbetweenaLANhubandamobiledataterminalequippedwithanantenna,suchasalaptopcomputerornotepadcomputer.Oneexampleoftheutilityofsuchaconnectionistoenableanemployeereturningfromatriptotransferdatafromapersonalportablecomputertoaserverintheoffice.Nomadicaccessisalsousefulinanextendedenvironmentsuchasacampusorabusinessoperatingoutofaclusterofbuildings.Inbothofthesecases,usersmaymovearoundwiththeirportablecomputersandmaywishaccesstotheserversonawiredLANfromvariouslocations.

4)

AdHocNetworking

Anadhocnetworkisapeertopeernetwork(nocentralizedserver)setuptemporarilytomeetsomeimmediateneed.Forexample,agroupofemployees,eachwithalaptoporpalmtopcomputermayconveneinaconferenceroomforabusinessorclassroommeeting.Theemployeeslinktheircomputersinatemporarynetworkjustforthedurationofthemeeting.Fig12.3suggeststhedifferencesbetweenawirelessLANthatsupportsLANextensionandnomadicaccessrequirementsandanadhocwirelessLAN.Intheformercase,thewirelessLANformsastationaryinfrastructureconsistingofoneormorecellswithacontrolmoduleforeachcell[6].Withinacell,theremaybeanumberofstationaryendsystems.Nomadicstationscanmovefromonecelltoanother.Incontrast,thereisnoinfrastructureforanadhocnetwork.Rather,apeercollectionofstationswithinrangeofeachothermaydynamicallyconfigurethemselvesintoatemporarynetwork.

Fig12.3WirelessLANconfigurations2．WirelessLANRequirements

AwirelessLANmustmeetthesamesoreofrequirementstypicalofanyLAN,includinghighcapacity,abilitytocovershortdistances,fullconnectivityamongattachedstations,andbroadcastcapability.Inaddition,thereareanumberofrequirementsspecifictothewirelessLANenvironment.ThefollowingareamongthemostimportantrequirementsforwirelessLANs:(1)Throughput:Themediumaccesscontrolprotocolshouldmakeasefficientuseaspossibleofthewirelessmediumtomaximizecapacity[7].

(2)Numberofnodes:WirelessLANsmayneedtosupporthundredsofnodesacrossmultiplecells.

(3)

ConnectiontobackboneLAN:

Inmostcases,interconnectionwithstationsonawiredbackboneLANisrequired.ForinfrastructurewirelessLANs,thisiseasilyaccomplishedthroughtheuseofcontrolmodulesthatconnecttobothtypesofLANs.Theremayalsoneedtobeaccommodationformobileusersandadhocwirelessnetworks.(4)

Servicearea:

AtypicalcoverageareaforawirelessLANhasadiameterof100to300m.

(5)

Batterypowerconsumption:Mobileworkersusebatterypoweredworkstationsthatneedtohavealongbatterylifewhenusedwithwirelessadapters.ThissuggeststhataMACprotocolthatrequiresmobilenodestomonitoraccesspointsconstantlyorengageinfrequenthandshakeswithabasestationisinappropriate.

NEWWORDSANDPHRASES

principl n. 負(fù)責(zé)人，首長，校長；主犯；本金

adj. 主要的，首要的

wireless adj. 無線的

occupy vt. 占，占用，占領(lǐng)，占據(jù)

significant adj. 有意義的，重大的，重要的

niche n. 壁龕，適當(dāng)?shù)奈恢胊djunct n. 附件，助手

adj. 附屬的

indispensable n. 不可缺少之物

adj. 不可缺少的，絕對必要的

relocation n. 再布置，變換布置

survey n. 測量，調(diào)查，俯瞰，概觀，縱覽，視察

vt. 調(diào)查(收入，民意等)，測量，勘定，審視，視察，俯瞰，通盤考慮

characteristic adj. 特有的，表示特性的，典型的

n. 特性，特征

vi. 測量土地

summarize vt. 概述，總結(jié)，摘要而言

approach n. 接近，逼近，走近；方法，步驟，途徑，通路

vt. 接近，動(dòng)手處理

vi. 靠近

spectrum n. 光，光譜，型譜，頻譜

narrowband n. 窄帶

interconnect vt. 使互相連接

modification n. 更改，修改，修正

substitute n. 代用品，代替者，替代品

vt.,vi. 代替，替換，替代motivation n. 動(dòng)機(jī)

awareness n. 知道，曉得

abundance n. 豐富，充裕

alternative n.二中擇一，可供選擇的辦法、事物

adj. 選擇性的，二中擇一的

backbone n. 脊椎，中樞，骨干，支柱，意志力，勇氣，毅力，決心

application n.請求，申請，申請表，應(yīng)用，運(yùn)用；應(yīng)用程序，應(yīng)用軟件nomadic adj. 游牧的，游動(dòng)的

temporarily adv. 臨時(shí)

convene vt.,vi. 召集，集合

peer n. 同等的人，貴族

vi. 凝視，窺視

vt. 與……同等，封為貴族

dynamical adj. 動(dòng)力(學(xué))，有力量的

specific n. 特效藥；細(xì)節(jié)

adj. 詳細(xì)而精確的，明確的，特殊的，特效的efficient adj. (直接)生效的，有效率的，能干的

coverage n. 覆蓋

consumption n. 消費(fèi)，消費(fèi)量；肺病

constantly adv. 不變地，經(jīng)常地，堅(jiān)持不懈地

inappropriate adj. 不適當(dāng)?shù)?，不相稱的

feature n. 面容(單數(shù)表示面容的一部分)；特色；特寫，特輯；特別節(jié)目；零件，部件；要素

eavesdroppingn. 偷聽；竊聽，竊[偷]聽技術(shù)

interference n. 沖突，干涉；干擾，串?dāng)_

thwart adj. 橫放的

vt. 反對，阻礙，橫過

adv.，prep. 橫過

n. [船]橫坐板unauthorized adj. 未被授權(quán)的，未經(jīng)認(rèn)可的

aspect n. 樣子，外表，面貌；(問題等的)方面

disruption n. 中斷，分裂，瓦解，破壞

penetrate vt. 穿透，滲透，看穿，洞察

vi. 刺入，看穿，滲透，彌漫

implementation n. 不透明物

NOTES

[1]Injustthepastfewyears,wirelessLANshavecometooccupyasignificantnicheinthelocalareanetworkmarket.

本句可譯為：在剛過去的幾年中，無線局域網(wǎng)已占據(jù)了局域網(wǎng)市場的重要份額。

[2]Forexample,amanufacturingfacilitytypicallyhasanofficeareathatisseparatefromthefactoryfloorbutthatmustbelinkedtoitfornetworkingpurposes.

句中“networking”是動(dòng)名詞延伸為名詞，譯為“聯(lián)網(wǎng)技術(shù)”，句中舉例說明了無線網(wǎng)絡(luò)的應(yīng)用價(jià)值。本句可譯為：例如，一個(gè)生產(chǎn)部門的辦公室和工作分開，但同時(shí)需要網(wǎng)絡(luò)聯(lián)接。

[3]Fig12.1indicatesasimplewirelessLANconfigurationthatistypicalofmanyenvironments.

句中“betypicalof”譯為“是……的典型”。

本句可譯為：圖12.1所示為一個(gè)典型的簡單無線局域網(wǎng)配置，適用于很多場合。

[4]TheconfigurationofFig12.1canbereferredtoasasinglecellwirelessLAN.

句中“bereferredto”是被動(dòng)語態(tài)，表示被查詢、被提到，在科技論文中一般使用被動(dòng)語態(tài)表示其敘述的客觀性。

本句可譯為：圖12.1所示的結(jié)構(gòu)稱為單區(qū)無線局域網(wǎng)。

[5]AnotheruseofwirelessLANtechnologyistoconnectLANsinnearbybuildings,bethewiredorwirelessLANs.

句中bethewiredorwirelessLANs是非限定性定語句whicharethewiredorwirelessLANs的縮略形式。

本句可譯為：無線局域網(wǎng)技術(shù)的另一種應(yīng)用是實(shí)現(xiàn)相鄰樓宇局域網(wǎng)(有線或無線局域網(wǎng))間的互聯(lián)。

[6]Intheformercase,thewirelessLANformsastationaryinfrastructureconsistingofoneormorecellswithacontrolmoduleforeachcell.

本句可譯為：在第一種案例中，無線局域網(wǎng)構(gòu)成了有一個(gè)或多個(gè)區(qū)的固定結(jié)構(gòu)，每個(gè)區(qū)有一個(gè)控制模塊。

[7]Themediumaccesscontrolprotocolshouldmakeasefficientuseaspossibleofthewirelessmediumtomaximizecapacity.

句中“makeasefficientuseaspossibleof”可譯為“盡可能高效地利用”，其核心為“makeuseof”;“asefficientuseaspossible”的意思是“豐富了其意義，加強(qiáng)了程度”。

本句可譯為：媒體訪問控制協(xié)議應(yīng)能保證無線媒介的使用效率達(dá)到最高容量。

EXERCISES

Ⅰ.

TranslatethefollowingwordsandphrasesintoEnglish.

低數(shù)據(jù)速率 靜態(tài)工作站 支持服務(wù)器

覆蓋區(qū)域 無線適配器 未授權(quán)訪問

Ⅱ.

TranslatethefollowingwordsandphrasesintoChinese.

(1)

significantniche (2)

spreadspectrum

(3)

narrowbandmicrowave (4)

networkstructure

(5)

twistedpair (6)

controlmodule(CM)

(7)

tokenpassingscheme (8)

usermodules(UMs)

(9)

multiplecell (10)

CrossBuilding

(11)

pointtopointwirelesslink (12)

NomadicAccess

(13)

peertopeernetwork (14)

stationaryinfrastructure

(15)

mobilestation (16)

mediumaccesscontrolprotocol

Ⅲ.

TranslatethefollowingparagraphsintoChinese.

(1)

Asthenamesuggests,awirelessLANisonethatmakesuseofawirelesstransmissionmedium.WirelessLANswerelittleused.Thereasonsforthisincludedhighprice,lowdatarates,occupationalsafetyconcerns,andlicensingrequirements.Astheseproblemshavebeenaddressed,thepopularityofwirelessLANshasgrownrapid.

(2)

EarlywirelessLANproducts,introducedinthelate1980s,weremarketedassubstitutesfortraditionalwiredLANs.AwirelessLANsavesthecostoftheinstallationofLANcablingandeasesthetaskofrelocationandothermodificationstonetworkstructure.However,thismotivationforwirelessLANswasovertakenbyevents.(3)

Anadhocnetworkisapeertopeernetwork(nocentralizedserver)setuptemporarilytomeetsomeimmediateneed.Forexample,agroupofemployees,eachwithalaptoporpalmtopcomputermayconveneinaconferenceroomforabusinessorclassroommeeting.Theemployeeslinktheircomputersinatemporarynetworkjustforthedurationofthemeeting.

參考譯文

第十二單元無線局域網(wǎng)技術(shù)

在剛過去的幾年中，無線局域網(wǎng)已占據(jù)了局域網(wǎng)市場的重要份額。網(wǎng)絡(luò)機(jī)構(gòu)也越來越發(fā)現(xiàn)無線局域網(wǎng)已成為傳統(tǒng)有線局域網(wǎng)不可或缺的附加部分，并以此來滿足下列需求：移動(dòng)性、再定位、自組織組網(wǎng)和覆蓋有線網(wǎng)絡(luò)難以布線的區(qū)域。

正如其名稱所示，無線局域網(wǎng)使用無線傳輸介質(zhì)。無線局域網(wǎng)過去很少被采用，原因是其價(jià)格高、傳輸速率低、安全得不到保障，且沒有標(biāo)準(zhǔn)許可。當(dāng)這些問題都被解決后，無線局域網(wǎng)的普及速度獲得了迅速增長。我們首先介紹無線局域網(wǎng)的需求和優(yōu)點(diǎn)，接著展望無線局域網(wǎng)實(shí)現(xiàn)的關(guān)鍵途徑。

1．無線局域網(wǎng)的應(yīng)用

無線局域網(wǎng)應(yīng)用于四個(gè)領(lǐng)域：局域網(wǎng)延伸、樓宇間互聯(lián)、游牧式接入和自組織組網(wǎng)。下面我們按順序分別介紹。

1)局域網(wǎng)延伸

20世紀(jì)80年代后期出現(xiàn)了無線局域網(wǎng)的早期產(chǎn)品，其市場定位是用于取代傳統(tǒng)的有線局域網(wǎng)。無線局域網(wǎng)節(jié)省了有線局域網(wǎng)線纜安裝費(fèi)用，并簡化了再定位和其他網(wǎng)絡(luò)結(jié)構(gòu)修改工作。然而，由于一些原因，無線局域網(wǎng)達(dá)到上述要求的能力被高估了。首先，由于知道用戶對局域網(wǎng)的需求日益增加，建筑師在設(shè)計(jì)新建筑時(shí)就已經(jīng)預(yù)留了用于數(shù)據(jù)應(yīng)用的預(yù)連線。其次，由于數(shù)據(jù)傳輸技術(shù)的優(yōu)勢，人們更信賴用雙絞線纜組建局域網(wǎng)，特別是用3類和5類非屏蔽雙絞線。很多老建筑都已經(jīng)布放了豐富的3類線纜，并且很多新建筑也預(yù)先布放了5類線。因此，用無線局域網(wǎng)替代有線局域網(wǎng)不能大范圍實(shí)現(xiàn)。但是，在一些情況下，無線局域網(wǎng)可取代有線局域網(wǎng)。例如，具有很大開放空間的建筑，諸如生產(chǎn)車間、股票交易大廳、倉庫；由于歷史原因雙絞線資源不足，且不允許為了新增布線而鉆孔的建筑；安裝和維護(hù)有線局域網(wǎng)不經(jīng)濟(jì)的小公司。在所有這些情況下，無線局域網(wǎng)就成為更有效、更具吸引力的替代。上述的大多數(shù)情況中，網(wǎng)絡(luò)體系結(jié)構(gòu)依然需要有線局域網(wǎng)來支持服務(wù)器和一些固定工作站。例如，一個(gè)生產(chǎn)部門的辦公室和工廠分開，但同時(shí)需要網(wǎng)絡(luò)聯(lián)接。這時(shí)，通常無線局域網(wǎng)將被接入到有線局域網(wǎng)來實(shí)現(xiàn)上述要求。所以，這種應(yīng)用場合就稱為局域網(wǎng)延伸。圖12.1所示為一個(gè)典型的簡單無線局域網(wǎng)配置，適用于很多場合。網(wǎng)中有一個(gè)骨干有線局域網(wǎng)(如以太網(wǎng))，用來支持服務(wù)器、工作站和一個(gè)或多個(gè)橋接器或路由器，以便接入其他網(wǎng)絡(luò)。除此之外，還有一個(gè)控制模塊(CM)，為與無線局域網(wǎng)連接提供接口?？刂颇K具有橋接或路由功能，可將無線局域網(wǎng)連接到骨干網(wǎng)絡(luò)。它還包含一些訪問控制邏輯，如輪詢或令牌傳遞方案，對末端系統(tǒng)訪問進(jìn)行調(diào)度管理。需注意的是，一些末端系統(tǒng)是獨(dú)立設(shè)備，如工作站或服務(wù)器。網(wǎng)中還有控制一定數(shù)量的有線局域網(wǎng)工作站的集線器或其他用戶模塊(UM)，它們也是無線局域網(wǎng)結(jié)構(gòu)的一部分。

圖12.1單區(qū)無線局域網(wǎng)配置實(shí)例

圖12.1所示的結(jié)構(gòu)稱為單區(qū)無線局域網(wǎng)，其中所有的無線終端系統(tǒng)都處于一個(gè)控制模塊的控制范圍中。另一種常見結(jié)構(gòu)如圖12.2所示，是一個(gè)多區(qū)無線局域網(wǎng)，由通過有線局域網(wǎng)互聯(lián)在一起的多個(gè)控制模塊控制。每個(gè)控制模塊支持位于其傳輸范圍內(nèi)的一定數(shù)量的無線終端設(shè)備。例如，對于紅外線局域網(wǎng)，其傳輸范圍限于一個(gè)房間中，因此，一個(gè)需要無線支持的辦公大樓，其每個(gè)房間都需要一個(gè)單區(qū)結(jié)構(gòu)無線局域網(wǎng)。

圖12.2多區(qū)無線局域網(wǎng)配置實(shí)例2)樓宇間互聯(lián)

無線局域網(wǎng)技術(shù)的另一種應(yīng)用是實(shí)現(xiàn)相鄰樓宇局域網(wǎng)(有線或無線局域網(wǎng))間的互聯(lián)。在該情況下，樓宇間需要實(shí)現(xiàn)一個(gè)點(diǎn)到點(diǎn)的無線連接。使用的設(shè)備一般為橋接器或路由器。這個(gè)點(diǎn)到點(diǎn)連接本質(zhì)上不是局域網(wǎng)，但是它通常被認(rèn)為是無線局域網(wǎng)應(yīng)用的一個(gè)發(fā)展方向。

3)游牧式接入

游牧式接入提供一個(gè)無線連接，使帶有天線的移動(dòng)數(shù)據(jù)終端設(shè)備(便攜式計(jì)算機(jī)或筆記本電腦)可無線接入到局域網(wǎng)集線器。這種連接應(yīng)用可以讓剛出差回來的員工立刻將其個(gè)人便攜式計(jì)算機(jī)上的數(shù)據(jù)上傳到公司的服務(wù)器。游牧式接入在一些范圍廣大的環(huán)境中也非常有用，如校園或企業(yè)的各個(gè)樓宇。上述兩個(gè)案例中，用戶可以帶著他們的便攜式計(jì)算機(jī)游走，通過游牧式接入功能接入到不同區(qū)域有線局域網(wǎng)的服務(wù)器中。

4)自組織組網(wǎng)

自組織網(wǎng)絡(luò)是一種層對層(peertopeer)的網(wǎng)絡(luò)(無中心式服務(wù)器)，根據(jù)緊急需求而臨時(shí)組建。例如，有一組員工，每人都有一臺(tái)便攜式或掌上電腦，在一個(gè)辦公室召開工作或?qū)W習(xí)會(huì)議。而只有在會(huì)議期間，員工們的電腦才接入這個(gè)臨時(shí)網(wǎng)絡(luò)。

圖12.3比較了支持局域網(wǎng)延伸的無線局域網(wǎng)、游牧式接入需求和自組織無線局域網(wǎng)的區(qū)別。在第一種案例中，無線局域網(wǎng)構(gòu)成了一種有一個(gè)或多個(gè)區(qū)的固定結(jié)構(gòu)，每個(gè)區(qū)中都有一個(gè)控制模塊。在一個(gè)區(qū)中，可能會(huì)有一定數(shù)量的固定終端系統(tǒng)。游牧式工作站可以從一個(gè)區(qū)移動(dòng)到另一個(gè)區(qū)。相反，自組織網(wǎng)絡(luò)中沒有基礎(chǔ)設(shè)備，位于一定范圍內(nèi)工作站間相互收集層信息，并以此來動(dòng)態(tài)地組建它們之間的臨時(shí)網(wǎng)絡(luò)。

圖12.3無線局域網(wǎng)配置2．對無線局域網(wǎng)的要求

無線局域網(wǎng)必須滿足任何局域網(wǎng)所滿足的一系列典型要求，包括大容量、短距離覆蓋能力、接入工作站間的全連通能力和廣播能力。除此之外，對無線局域網(wǎng)環(huán)境還有一些特殊要求。無線局域網(wǎng)最重要的要求如下所列：

(1)吞吐量：媒體訪問控制協(xié)議應(yīng)能保證無線媒介的使用效率達(dá)到最高容量。

(2)節(jié)點(diǎn)數(shù)量：無線局域網(wǎng)應(yīng)能支持多區(qū)上百個(gè)節(jié)點(diǎn)。(3)接入骨干局域網(wǎng)：在大多數(shù)情況下，需要與骨干局域網(wǎng)上的工作站互聯(lián)。對于基本結(jié)構(gòu)的無線局域網(wǎng)，通過使用連接到兩類局域網(wǎng)的控制器就很容易實(shí)現(xiàn)這種互聯(lián)。此外,還應(yīng)適應(yīng)移動(dòng)用戶和自組織無線網(wǎng)絡(luò)。

(4)服務(wù)范圍：無線局域網(wǎng)的典型覆蓋范圍是直徑為100

m～300

m的區(qū)域。

(5)電池電力消耗：移動(dòng)狀態(tài)的工作者使用電池供電的工作站，當(dāng)使用無線接入點(diǎn)時(shí)需要電池供電時(shí)間長。這意味著MAC(MediumAccessControl)協(xié)議不再適用，因?yàn)樗鼤?huì)讓移動(dòng)節(jié)點(diǎn)持續(xù)監(jiān)控接入點(diǎn)或平凡地與基站進(jìn)行握手信號交換。

EXTENSIVETEXT

Bluetooth

Bluetoothwirelesstechnologyisashort-rangecommunicationstechnologyinintendedtoreplacethecablesconnectingportableandfixeddeviceswhilemaintaininghighlevelsofsecurity.ThekeyfeaturesofBluetoothtechnologyarerobustness,lowpower,andlowcost.TheBluetoothspecificationdefinesauniformstructureforawiderangeofdevicestoconnectandcommunicatewitheachother.BluetoothtechnologyhasachievedglobalacceptancesuchthatanyBluetoothenableddevice,almosteverywhereintheworld,canconnecttootherBluetoothenableddevicesinproximity.Bluetoothenabledelectronicdevicesconnectandcommunicatewirelesslythroughshort-range,adhocnetworksknownaspiconets.Eachdevicecansimultaneouslycommunicatewithuptosevenotherdeviceswithinasinglepiconet.Eachdevicecanalsobelongtoseveralpiconetssimultaneously.PiconetsareestablisheddynamicallyandautomaticallyasBluetoothenableddevicesenterandleaveradioproximity.AfundamentalBluetoothwirelesstechnologystrengthistheabilitytosimultaneouslyhandlebothdataandvoicetransmissions.Thisenablesuserstoenjoyvarietyofinnovativesolutionssuchasahands-freeheadsetforvoicecalls,printingandfaxcapabilities,synchronizingPDA,laptop,andmobilephoneapplicationstonameafew.

1．Coresystem

TheBluetoothcoresystem,definedbyBluetoothspecification,isacommonservicelayerprotocolwhichcoversfourlowerlayersinsevenlayerprotocol.ServiceDiscoveryProtocol(SDP)andtheoverallprofilerequirementsaredefinedbyGenericAccessProfile(GAP).AcompleteBluetoothapplicationrequiresanumberofadditionalservicesandhigherlayerprotocolsthataredefinedintheBluetoothspecification.ThelowestthreelayersaresometimesgroupedintoasubsystemknownastheBluetoothcontroller.ThisisacommonimplementationinvolvingastandardphysicalcommunicationsinterfacebetweentheBluetoothcontrollerandremainderoftheBluetoothsystemincludingtheL2CAP,servicelayersandhigherlayers(knownastheBluetoothhost).Althoughthisinterfaceisoptional,thearchitectureisdesignedtoallowforitsexistenceandcharacteristics.TheBluetoothspecificationenablesinteroperabilitybetweenindependentBluetoothenabledsystemsbydefiningtheprotocolmessagesexchangedbetweenequivalentlayers,andalsointeroperabilitybetweenindependentBluetoothsub-systemsbydefiningacommoninterfacebetweenBluetoothcontrollersandBluetoothhosts.

Anumberoffunctionalblocksareshownandthepathofservicesanddatabetweenthese.Thefunctionalblocksshowninthediagramareinformative;ingeneraltheBluetoothspecificationdoesnotdefinethedetailsofimplementationsexceptwherethisisrequiredforinteroperability.Standardinteractionsaredefinedforallinter-deviceoperation,whereBluetoothdevicesexchangeprotocolsignalingaccordingtotheBluetoothspecification.TheBluetoothcoresystemprotocolsaretheradio(RF)protocol,linkcontrol(LC)protocol,linkmanager(LM)protocolandlogicallinkcontrolandadaptationprotocol(L2CAP),allofwhicharefullydefinedinsubsequentpartsoftheBluetoothspecification.Inaddition,theservicediscoveryprotocol(SDP)isaservicelayerprotocolrequiredbyallBluetoothapplications.TheBluetoothcoresystemoffersservicesthroughanumberofserviceaccesspointsthatareshowninthediagramasellipses.TheseservicesconsistofthebasicprimitivesthatcontroltheBluetoothcoresystem.Theservicescanbesplitintothreetypes.TherearedevicecontrolservicesthatmodifythebehaviorandmodesofaBluetoothdevice,transportcontrolservicesthatcreate,modifyandreleasetrafficbearers(channelsandlinks),anddataservicesthatareusedtosubmitdatafortransmissionovertrafficbearers.ItiscommontoconsiderthefirsttwoasbelongingtotheC-planeandthelastasbelongingtotheU-plane.AserviceinterfacetotheBluetoothcontrollersub-systemisdefinedsuchthattheBluetoothcontrollermaybeconsideredastandardpart.InthisconfigurationtheBluetoothcontrolleroperatesthelowestthreelayersandtheL2CAPlayeriscontainedwiththerestoftheBluetoothapplicationinahostsystem.Thestandardinterfaceiscalledthehosttocontrollerinterface(HCI).Implementationofthisstandardserviceinterfaceisoptional.AstheBluetootharchitectureisdefinedwiththepossibilityofaseparatehostandcontrollercommunicatingthroughanHCI,anumberofgeneralassumptionsaremade.TheBluetoothcontrollerisassumedtohavelimiteddatabufferingcapabilitiesincomparisonwiththehost.ThereforetheL2CAPlayerisexpectedtocarryoutsomesimpleresourcemanagementwhensubmittingL2CAPPDUstothecontrollerfortransporttoapeerdevice.ThisincludessegmentationofL2CAPSDUsintomoremanageablePDUsandthenthefragmentationofPDUsintostartandcontinuationpacketsofasizesuitableforthecontrollerbuffers,andmanagementoftheuseofcontrollerbufferstoensureavailabilityforchannelswithqualityofservice(QoS)commitments.ThebasebandlayerprovidesthebasicARQprotocolinBluetoothtechnology.TheL2CAPlayercanoptionallyprovideafurthererrordetectionandretransmissiontotheL2CAPPDUs.Thisfeatureisrecommendedforapplicationswithrequirementsforalowprobabilityofundetectederrorsintheuserdata.AfurtheroptionalfeatureofL2CAPisawindow-basedflowcontrolthatcanbeusedtomanagebufferallocationinthereceivingdevice.BothoftheseoptionalfeaturesaugmenttheQoSperformanceincertainscenarios.AlthoughtheseassumptionsmaynotberequiredforembeddedBluetoothtechnologyimplementationsthatcombinealllayersinasinglesystem,thegeneralarchitecturalandQoSmodelsaredefinedwiththeseassumptionsinmind,ineffectalowestcommondenominator.AutomatedconformancetestingofimplementationsoftheBluetoothcoresystemisrequired.ThisisachievedbyallowingthetestertocontroltheimplementationthroughtheRFinterface,WhichiscommontoallBluetoothsystems,andthroughthetestcontrolinterface(TCI),whichisonlyrequiredforconformancetesting.Thetesterusesexchangeswiththeimplementationundertest(IUT)throughtheRFinterfacetoensurethecorrectresponsestorequestsfromremotedevices.ThetestercontrolstheIUTthroug