ShengTzong Cheng 5222021 stchengmail ncku edu tw http

校園無線網路技術與應用發展 Sheng-Tzong Cheng 鄭憲宗 5/22/2021 stcheng@mail. ncku. edu. tw http: //plato. iie. ncku. edu. tw 06 -2757575 ext. 62529 1

成大資訊 鄭憲宗 無線區域網路通訊協定 Wireless Local Area Network (IEEE 802. 11) 5/22/2021 3

成大資訊 鄭憲宗 無線區域網路標準-IEEE 802. 11 n n Specifies a single Medium Access Control (MAC) sublayer and 3 Physical Layer Specifications. Stations can operate in two configurations : n n n Three PHY specifications n n n 5/22/2021 Ad-hoc mode Infrastructure mode Frequency Hopping Spread Spectrum (FHSS). Direct Sequence Spread Spectrum (DSSS). Infrared PHY. 4

成大資訊 鄭憲宗 IEEE 802. 11規範 Application Layer n IEEE Project 802 Charter: n n Local & Metropolitan Area Network 1 Mbps to 100 Mbps and higher 2 lower layers of 7 Layer OSI Reference Model IEEE 802. 11 Working Group. Data Link scope: Layer Wireless connectivity for fixed, portable and moving stations within a limited area n Appear to higher layer (LLC) the 5/22/2021 same as existing 802 standards . . . Network Layer LLC MAC n IEEE 802. 11 Physical Layer 5

成大資訊 鄭憲宗 IEEE 802. 11架構 n 1997/6/26通過成為IEEE 802系列標準 Logical Link Control Media Access Control Infrared Physical Layer 5/22/2021 FHSS Physical Layer DSSS Physical Layer 6

成大資訊 鄭憲宗 Ad Hoc網路 • One Basic Service Set • Directed Connection • Limited Coverage Area 5/22/2021 7

成大資訊 鄭憲宗 Infrastructure網路 Existing Wired LAN Distribution System Other LANs AP AP BSS Basic Service Set Extend Service Set 5/22/2021 8

成大資訊 鄭憲宗 Infrastructure網路 (cont. ) n n n n Access Point and Mobile Station Distributed System Interconnect Multiple Cells via Access Points to form a single network Extends Wireless Coverage Area Multiple Basic Service Sets connected together form an Extended Service Set Allow Mobile Station to access fixed resource Support Roaming for Mobile Stations via Access Point Coordination Function, Power Management, Time Synchronization support through Access Point 5/22/2021 9

成大資訊 鄭憲宗 IEEE 802. 11 Services n n n Provides 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 Avoidance (CSMA/CA) MAC services n n n 5/22/2021 Association service Authentication service Distribution service Integration service Deauthentication/Deassociation service 10

成大資訊 鄭憲宗 Spread Spectrum Technology n DSSS（Direct Sequence Spread Spectrum） n n FHSS（Frequency Hopping Spread Spectrum） n n n 11 channels PN-code長度為 11 -bit 展頻寬度為 11 MHz 78 hop sequences 頻帶範圍為 1 MHz， 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 公室環境使用；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。 11 5/22/2021

成大資訊 鄭憲宗 IEEE 802. 11 TGa n n The TGa is working on the high data-rate extension in the 5 GHz band, project 802. 11 a, was able to produce a new draft standard that has the support of at least 80 % of the members. TGa is looking at a candidate for worldwide standardization! 5/22/2021 14

成大資訊 鄭憲宗 IEEE 802. 11 TGa (cont. ) n n n 5/22/2021 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. Optional extensions are for 9, 18, 36, 48 and 54 Mbit/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. 15

成大資訊 鄭憲宗 IEEE 802. 11 TGb n n 5/22/2021 The TGb is working on the extension of the 1 and 2 Mbit/s data rates in the 2. 45 GHz band with 5. 5 and 11 Mbit/s has reached a technical compromise solution to improve the coexistence and interoperability characteristics between options. The multi-rate mechanism warrants that the 11 Mbit/s operation can switch back to 5. 5 Mbit/s. Stations that are even further could switch back to the 2 and 1 Mbit/s capabilities of the DSSS modulation. 16

成大資訊 鄭憲宗 CSMA/CD (LAN) n Send data if the medium is sensed “idle” If collides with other host(s), then backoff for a random number of times Re-send data later 5/22/2021 17 n n

成大資訊 鄭憲宗 Hidden Terminal Problem data A 5/22/2021 B data C 18

成大資訊 鄭憲宗 Solution to HTP Request A B C Grant 5/22/2021 19

成大資訊 鄭憲宗 Detection of Collision Request A 5/22/2021 B Request C 20

成大資訊 鄭憲宗 Collision Avoidance D Request A A is Grant 5/22/2021 B C A is Grant 21

成大資訊 鄭憲宗 RTS/CTS/data/ACK and NAV setting 5/22/2021 22

成大資訊 鄭憲宗 Some IFS relationships and basic access method 5/22/2021 23

成大資訊 鄭憲宗 Random backoff time n n n 5/22/2021 Backoff time = INT(CW * Random())*a. Slot. Time INT(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, 255……) Random() : 介於 0到 1間的實數 a. Slot. Time : 傳送器開啟延遲 + 媒介傳遞延遲 + 媒介忙碌偵測反應時間 24

成大資訊 鄭憲宗 An example of exponential increase of CW 5/22/2021 25

成大資訊 鄭憲宗 Backoff procedure 5/22/2021 26

成大資訊 鄭憲宗 Transmission of a multifragment MPDU using SIFS 5/22/2021 27

成大資訊 鄭憲宗 RTS/CTS with fragmented MSDU 5/22/2021 28

成大資訊 鄭憲宗 RTS/CTS with transmitter priority and missed acknowledgment 5/22/2021 29

成大資訊 鄭憲宗 Direct data/ACK MPDU 5/22/2021 30

成大資訊 鄭憲宗 無線區域網路軟體技術架構 Network Applications WLAN Management Utility File Transfer E-Mail Mobile IP SNMP Agent 5/22/2021 Security Mobile Data Distributed Service Socket Interface Network Driver (NDIS) Embedded Control Software WLAN Platform Remote Access Media Access Control U-NII or ISM band DSSS FHSS ETSI DECT 31

成大資訊 鄭憲宗 無線應用通訊協定 Wireless Application Protocol (WAP) 5/22/2021 32

成大資訊 鄭憲宗 What’s WAP for? n n n 5/22/2021 bring the internet content and advanced services to 後PC 時代之users create a global wireless protocol to work across differing wireless network technologies enable applications to scale across a variety of transport options and device types 41

成大資訊 鄭憲宗 What is defined in WAP? n n n 5/22/2021 Micro-Browser Scripting to enhance MS capabilities WTA/WTAI for telephone functionality (e. g. call chains) Content Formats n business card (v. Card ) n calendar event (v. Calendar ) Layered Telecommunication Stack 42

成大資訊 鄭憲宗 Comparison 5/22/2021 43

成大資訊 鄭憲宗 Goals for WTP (WAP v 1. 1) n n 5/22/2021 a common interface to physical transport mechanisms provide a port- based abstract interface to upper layer protocols allow applications designed independent from specific transports extensible to a variety of digital wireless networks and future transport options 45

成大資訊 鄭憲宗 Goals for WTP (cont. ) n n n supports connection- oriented, transaction, and datagram modes optimize for narrow to medium bandwidth channels to be capable of implementation in a low memory footprint, suitable for standard or low- IQ handsets 5/22/2021 46

成大資訊 鄭憲宗 Requirements for WTP n n WTP/ C provides a reliable connectionoriented service to the upper layer WTP/ T provides a reliable transactionoriented service suitable for web browsing WTP/ D provides a datagram service lightweight : implementable in <= 10 Kb (low memory / computational needs) 5/22/2021 47

成大資訊 鄭憲宗 WTP/D features (WDP in WAP v 1. 2) n n n WTP/ D (Datagram) provides a connectionless, unreliable datagram service WTP/ D is replaced by UDP when used over an IP network layer. uses the Service Primitive n 5/22/2021 T- Unit. Data. req. ind 48

成大資訊 鄭憲宗 WAP v 1. 2 Wireless Application Environment (WAE Other Services and ) Applications Wireless Session Protocol (WSP) Wireless Transaction Protocol (WTP) Wireless Transport Layer Security (WTLS) Datagrams (UDP/IP) Datagrams (WDP) Wireless Bearers: SMS 5/22/2021 USSD CSD IS-136 CDMA IDEN CDPD PDC -P GPRS 49

成大資訊 鄭憲宗 WTP/T features (WTP in WAP v 1. 2) n n WTP/ T (Transaction) provides reliable data transfer based on request/ reply paradigm no explicit connection setup or tear down data carried in first packet of protocol exchange seeks to reduce 3 - way handshake on initial request 5/22/2021 50

成大資訊 鄭憲宗 WTP/T features (cont. ) n n n 5/22/2021 supports n retransmission of lost packets n selective- retransmission n segmentation / re- assembly n port number addressing (specific to WTP/ T) n flow control message oriented (not stream) supports an Abort function for outstanding requests 51

成大資訊 鄭憲宗 Wireless Session Protocol n n n WSP/ B provides upper layers with session services and management WSP/ B Provides semantics and mechanisms based on HTTP 1. 1 WSP provides means to : n n 5/22/2021 establish a reliable session from client to server agree on common level of protocol functionality by capability negotiation compact encoding suspend and resume 52

成大資訊 鄭憲宗 WSP features n n n 5/22/2021 HTTP 1. 1 functionality Exchange of client and server session headers Interrupt mechanism for transactions in process Content Push from server to client Negotiation for multiple, simultaneous asynchronous transactions 53

成大資訊 鄭憲宗 WTLS Record Protocol n 4 record protocol clients: n n n handshake protocol change cipher spec protocol alert protocol application data protocol WTLS connection state : the operating environment for record protocol n n 5/22/2021 The The compression/ encryption algorithm MAC algorithm -- keys 54

成大資訊 鄭憲宗 Record Protocol Usage n Handshake protocol n n n Change cipher spec protocol n n n Signal transitions in ciphering strategies sent before verifying finished message Alert protocol n 5/22/2021 Negotiate secure attributes of a secure session authentication, security parameter settings convey the severity of the message and a description of the alert 55

Wireless Application Environment (WAE) n n n An Internet (WWW) programming model Vendor- controlled MMI Initial focus on phones n n n 5/22/2021 成大資訊 鄭憲宗 Slow bearers Small memory Limited CPU Small screen Limited input model 56

成大資訊 鄭憲宗 WAE Components • Architecture – Application model – Browser, Gateway, Content Server • WML (Wireless Markup Language) – Display language • WMLScript – Scripting language • Content Formats – Data exchange 5/22/2021 57

成大資訊 鄭憲宗 WAE In- Device Architecture 5/22/2021 58

成大資訊 鄭憲宗 WML n Tag- based browsing language: n n n Screen management (text, images) Data input (text, selection lists, etc. ) Hyperlinks & navigation support Syntax: W 3 C XML (SGML derivative) Inherits technology from HDML and HTML 5/22/2021 59

成大資訊 鄭憲宗 WML (cont. ) n Card metaphor n n n State management and variables n n n Reduce network traffic Results in better caching Explicit inter- card navigation model n n 5/22/2021 User interactions are split into cards Navigation occurs between cards n Hyperlinks UI Event handling History 60

成大資訊 鄭憲宗 WML Example <? xml version="1. 0"? > <!DOCTYPE wml PUBLIC "-//WAPFORUM//DTD WML 1. 1//EN" "http: //www. wapforum. org/DTD/wml_1. 1. xml"> <wml> <card id="main"> <do type="accept"> <go href="#ecard"/> </do> <p>Welcome!</p> </card> <card id="ecard"> <do type="accept"> <go href="#ecard N=$(N); S=$(S)" /> </do> <p> Enter name: <input name="N"/> speed: <select name="S"> <option value="0">Fast</option> <option value="1">Slow</option> </select> </p> </card> 5/22/2021 </wml> 61

成大資訊 鄭憲宗 WMLScript n Scripting language: n n Derived from Java. Script™ Integrated with WML n n 5/22/2021 Procedural logic, loops, conditionals, etc. Optimized for small- memory, small- cpu devices Powerful extension mechanism Reduces overall network traffic 62

成大資訊 鄭憲宗 WMLScript (cont. ) n Bytecode-based virtual machine n n Compiler in network n n 5/22/2021 Stack-oriented design ROM-able Designed for simple, low-impact implementation Better network bandwidth use Better use of terminal memory/ cpu 63

成大資訊 鄭憲宗 WAP Gateway 5/22/2021 67

成大資訊 鄭憲宗 WAP Application Server 5/22/2021 68

成大資訊 鄭憲宗 WAP Push Technology Push Overthe-Air Protocol Push Access Protocol WAP Client Push Initiator Push Proxy Gateway 5/22/2021 70