校园无线网路技术与应用发展( 82页)-英文版ppt课件

1、校園無線網路技術與應用發展Sheng-Tzong Cheng 鄭憲宗stcheng.tw.twOutline無線區域網路 IEEE 802.11無線應用通訊協定 WAP無線區域網路通訊協定Wireless Local Area Network(IEEE 802.11)無線區域網路標準-IEEE 802.11Specifies a single Medium Access Control (MAC) sublayer and 3 Physical Layer Specifications.Stations can operate in two configurations :Ad-hoc mod

2、eInfrastructure modeThree PHY specificationsFrequency Hopping Spread Spectrum (FHSS).Direct Sequence Spread Spectrum (DSSS).Infrared PHY. IEEE 802.11規範IEEE Project 802 Charter:Local & Metropolitan Area Network1Mbps to 100Mbps and higher2 lower layers of 7 Layer OSI Reference ModelIEEE 802.11 Working

3、 Group scope:Wireless connectivity for fixed, portable and moving stations within a limited areaAppear to higher layer (LLC) the same as existing 802 standardsApplication LayerNetwork LayerMACPhysical Layer.LLCIEEE802.11 DataLinkLayer1997/6/26通過成為IEEE 802系列標準IEEE 802.11架構Media Access ControlLogical

4、Link Control InfraredPhysical Layer FHSSPhysical Layer DSSSPhysical LayerAd Hoc網路One Basic Service SetDirected ConnectionLimited Coverage AreaAPBSSInfrastructure網路APBasicServiceSetExistingWired LANDistribution SystemOtherLANsExtend Service SetInfrastructure網路 (cont.)Access Point and Mobile StationDi

5、stributed System Interconnect Multiple Cells via Access Points to form a single networkExtends Wireless Coverage AreaMultiple Basic Service Sets connected together form an Extended Service SetAllow Mobile Station to access fixed resourceSupport Roaming for Mobile Stations via Access PointPoint Coord

6、ination Function, Power Management, Time Synchronization support through Access PointIEEE 802.11 ServicesProvides services with the following functionality: roaming within a ESS, multiple data rates in BSSs and Power Management.The MAC protocol is Carrier Sense Multiple Access with Collision Avoidan

7、ce (CSMA/CA)MAC servicesAssociation serviceAuthentication serviceDistribution serviceIntegration serviceDeauthentication/Deassociation serviceSpread Spectrum TechnologyDSSSDirect Sequence Spread Spectrum11channelsPN-code長度為11-bit展頻寬度為11MHzFHSSFrequency Hopping Spread Spectrum78 hop sequences頻帶範圍為1MH

8、z，跳頻的頻率為每秒2.5次Infrared Ray發展趨勢：DHSS往高速無線區域網路系統發展，適合辦公室環境运用；FHSS會往低價網路應用發展，提供SOHO及家庭應用、或周邊設備之無線網路連結。直接序列展頻DSSS跳頻展頻FHSSIEEE 802.11 TGaThe TGa is working on the high data-rate extension in the 5 GHz band, project 802.11a, was able to produce a new draft standard that has the support of at least 80 % of

9、 the members.TGa is looking at a candidate for worldwide standardization! IEEE 802.11 TGa (cont.)The specifications of the Physical Layer encompass data rates from 6 Mbit/s up to 54 Mbit/s, with 20 MHz spacing between adjacent channels. All implementations are required to support 6, 12 and 24 Mbit/s

10、. Optional extensions are for 9, 18, 36, 48 and 54Mbit/s. The multi-rate mechanism of the MAC protocol ensures that all devices communicate with each other at the best data rate in the present channel. IEEE 802.11 TGbThe TGb is working on the extension of the 1 and 2 Mbit/s data rates in the 2.45 GH

11、z band with 5.5 and 11 Mbit/s has reached a technical compromise solution to improve the co-existence and interoperability characteristics between options. The multi-rate mechanism warrants that the 11 Mbit/s operation can switch back to 5.5Mbit/s. Stations that are even further could switch back to

12、 the 2 and 1 Mbit/s capabilities of the DSSS modulation. CSMA/CD (LAN)Send data if the medium is sensed “idleIf collides with other host(s),then backoff for a random number of timesRe-send data laterHidden Terminal Problem BACdatadataSolution to HTPBA CRequestGrantDetection of CollisionBA CRequestRe

13、questBA CRequestA is GrantA is GrantDCollision AvoidanceRTS/CTS/data/ACK and NAV settingSome IFS relationships and basic access methodRandom backoff timeBackoff time = INT(CW * Random()*aSlotTimeINT(x) : 小於或等於x的最大整數CW(contention window parameter ) : 介於CWmin和Cwmax間的整數 , CW依序遞增的順序為(7,15,31,63,127,255,

14、255,255)Random() : 介於0到1間的實數aSlotTime : 傳送器開啟延遲 + 媒介傳遞延遲 + 媒介忙碌偵測反應時間An example of exponential increase of CWBackoff procedureTransmission of a multi-fragment MPDU using SIFS RTS/CTS with fragmented MSDURTS/CTS with transmitter priority and missed acknowledgmentDirect data/ACK MPDU無線區域網路軟體技術架構WLAN P

15、latformEmbedded ControlSoftwareWLAN ManagementUtilityNetworkApplicationsDSSSFHSSMedia Access ControlNetwork Driver (NDIS)Socket InterfaceMobile IPSNMPAgentSecurityDistributedService File TransferRemote AccessMobile DataDECTU-NII or ISM bandETSI無線應用通訊協定Wireless Application Protocol(WAP)無線上網趨勢日本NTT的Do

16、CoMo 於2/1999推出無線上網服務，一年內累積3百萬用戶，每週添加10萬人WAP Forum於1997年成立，至1999年12月全世界有200家無線通訊事業成為會員(95%市場之相關業者投入)1999年，WAP是手機运用者最熱門話題之一無線上網趨勢 (續)1999年在台灣銷售180萬隻手機前兩大廠 Motorola 於 2000上半年WAP手機佔40% ，下半年100%投入；Nokia 則佔30%。國內新上市的手機六到七成內建WAP功能台灣已超過1000萬人有行動手機，而PC上網人數約3至4百萬語音：數據95% : 5% (2000) ; 40% : 60% (2005)全球無線通訊用戶

17、成長預估未來WAP手機的佔有率手持型元件之延革bring the internet content and advanced services to 後PC 時代之userscreate a global wireless protocol to work across differing wireless network technologies enable applications to scale across a variety of transport options and device typesWhats WAP for?What is defined in WAP?Micr

18、o-BrowserScripting to enhance MS capabilitiesWTA/WTAI for telephone functionality (e.g. call chains)Content Formatsbusiness card (vCard )calendar event (vCalendar )Layered Telecommunication StackComparisonGoals for WTP (WAP v1.1)a common interface to physical transport mechanismsprovide a port- base

19、d abstract interface to upper layer protocolsallow applications designed independent from specific transportsextensible to a variety of digital wireless networks and future transport optionsGoals for WTP (cont.)supports connection- oriented, transaction, and datagram modesoptimize for narrow to medi

20、um bandwidth channelsto be capable of implementation in a low memory footprint, suitable for standard or low- IQ handsetsRequirements for WTPWTP/ C provides a reliable connection- oriented service to the upper layerWTP/ T provides a reliable transaction- oriented service suitable for web browsingWTP

21、/ D provides a datagram servicelightweight : implementable in = 10Kb (low memory / computational needs)WTP/D features (WDP in WAP v 1.2)WTP/ D (Datagram) provides a connection- less, unreliable datagram serviceWTP/ D is replaced by UDP when used over an IP network layer.uses the Service PrimitiveT-

22、UnitData. req .indWAP v 1.2Wireless Bearers:SMSUSSDCSDIS-CDMAIDENCDPDPDC-PGPRSWireless Application Environment (WAE)Wireless Session Protocol (WSP)Wireless Transaction Protocol (WTP)Wireless Transport Layer Security (WTLS)Datagrams(UDP/IP)Datagrams(WDP)Other Services andApplicationsWireless Bearers:

23、SMSUSSDCSDIS-CDMAIDENCDPDPDC-PGPRSWireless Application Environment (WAE)Wireless Session Protocol (WSP)Wireless Transaction Protocol (WTP)Wireless Transport Layer Security (WTLS)Datagrams(UDP/IP)Datagrams(WDP)Other Services andApplicationsWTP/T features (WTP in WAP v 1.2) WTP/ T (Transaction) provid

24、es reliable data transfer based on request/ reply paradigmno explicit connection setup or tear downdata carried in first packet of protocol exchangeseeks to reduce 3- way handshake on initial requestWTP/T features (cont.) supportsretransmission of lost packetsselective- retransmissionsegmentation /

25、re- assemblyport number addressing (specific to WTP/ T)flow controlmessage oriented (not stream)supports an Abort function for outstanding requestsWireless Session Protocol WSP/ B provides upper layers with session services and managementWSP/ B Provides semantics and mechanisms based on 1.1WSP provi

26、des means to : establish a reliable session from client to serveragree on common level of protocol functionality by capability negotiationcompact encodingsuspend and resumeWSP features 1.1 functionalityExchange of client and server session headersInterrupt mechanism for transactions in processConten

27、t Push from server to clientNegotiation for multiple, simultaneous asynchronous transactionsWTLS Record Protocol 4 record protocol clients:The handshake protocolThe change cipher spec protocolThe alert protocolThe application data protocolWTLS connection state : the operating environment for record

28、protocolcompression/ encryption algorithmMAC algorithm - keysRecord Protocol Usage Handshake protocolNegotiate secure attributes of a secure sessionauthentication, security parameter settingsChange cipher spec protocolSignal transitions in ciphering strategiessent before verifying finished messageAl

29、ert protocol convey the severity of the message and a description of the alert Wireless Application Environment (WAE) An Internet (WWW) programming model Vendor- controlled MMI Initial focus on phones Slow bearers Small memory Limited CPU Small screen Limited input model WAE Components Architecture

30、Application model Browser, Gateway, Content Server WML (Wireless Markup Language) Display language WMLScript Scripting languageContent Formats Data exchange WAE In- Device ArchitectureWML Tag- based browsing language:Screen management (text, images)Data input (text, selection lists, etc.)Hyperlinks

31、& navigation supportSyntax: W3C XML (SGML derivative)Inherits technology from HDML and HTMLWML (cont.) Card metaphorUser interactions are split into cardsNavigation occurs between cardsState management and variables Reduce network traffic Results in better cachingExplicit inter- card navigation modelHyperlinksUI Event handlingHistoryWML Example Welcom