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1、1,Wireless Internet: Protocols and Performance,SDUST Information Science and Technology Institute Fang Sheng,2,Tutorial Outline,1. Introduction/Motivation (10 min) 2. Networking Terminology (10 min) 3. IEEE 802.11b WLANs (10 min) 4. Ad hoc networks(10 min)5. Summary, Questions, Discussion (5 min),3,
2、1. Wireless Internet: Introduction,4,What Is Wireless Networking?,The use of infra-red (IR) or radio frequency (RF) signals to share information and resources between devices A hot computer industry buzzword: Lots of advertising by companies and media Wireless Broadband, 3G wireless, 4G, WAP, iMode,
3、 Bluetooth, WiFi Mobile Internet, Pervasive Computing, Nomadic Computing, M-commerce Ubiquitous; Global; Revolutionary,5,Two Popular 2.4 GHz Standards:,IEEE 802.11 Fast (11b) High Power Long range Ethernet replacement Easily Available Apple Airport, iBook, G4 Cisco Aironet 350,Bluetooth Slow Low Pow
4、er Short range Cable replacement “Vapourware” (?),6,IEEE 802.11 Organization Tree:,7,Pros and Cons of 802.11:,Pro: High bandwidth (up to 11 Mbps) Two modes of operation: infrastructure vs. ad hoc Con: Incompatibility between old and new cards Signal blocked by reinforced concrete or tinted glass Hig
5、h channel BER can degrade performance (lots!) No standard for hand-off between base stations Some channel numbers overlap spectrum High power consumption in laptops,8,Bluetooth,Think USB, not Ethernet Cable replacement technology Created by Ericsson PAN - Personal Area Network 1-2 Mbps connections 1
6、600 hops per second FHSS Includes synchronous, asynchronous, voice connections Piconet routing Small, low-power, short-range, cheap, versatile radios Used as Internet connection, phone, or headset Master/slave configuration and scheduling,9,Security,Wireless sniffers, “war driving” IEEE 802.11: ESSI
7、D Extended Services Set ID WEP Wired Equivalent Privacy (useless) NAT - Network Address Translation (firewall) Bluetooth Security FHSS, with rapid hop sequence Short range Encrypted transmissions (optional),10,Future of Wireless,Higher data rates Better security Wider selection of products Lower pri
8、ces Zero configuration networking More end-user focus Better software Less visible More popular,11,2. Background: Networking Terminology,12,Wireless Internet Technologies,Mobile devices (e.g., notebooks, laptops, PDAs, cell phones, wearable computers) Wireless network access Bluetooth (1 Mbps, up to
9、 3 meters) IEEE 802.11b (11 Mbps, up to 100 meters) IEEE 802.11a (55 Mbps, up to 20 meters) Operating modes: Infrastructure mode (access point) Ad hoc mode Wireless Web, WiFi “hot spots”,13,Internet Protocol Stack,Application: supporting network applications and end-user services FTP, SMTP, HTTP, DN
10、S, NTP Transport: end to end data transfer TCP, UDP Network: routing of datagrams from source to destination IPv4, IPv6, BGP, RIP, routing protocols Data Link: hop by hop frames, channel access, flow/error control PPP, Ethernet, IEEE 802.11b Physical: raw transmission of bits,001101011.,14,Internet
11、Protocol Stack,Application: e.g., Hyper-Text Transfer Protocol (HTTP) Transport: Transmission Control Protocol (TCP) User Datagram Protocol (UDP) Network: Internet Protocol (IP, IPv4, IPv6) Data Link: e.g., IEEE 802.3 Ethernet, IEEE 802.11b Physical: Device specific, network specific,001101011.,15,M
12、ulti-Hop Wireless Ad Hoc Networks,Routing protocols used to improve wireless connections Infrastructure-free, dynamic True Peer-to-Peer routing Fault tolerantExamples: AODV, DSDV, TORA, DSR, .,16,Example:,Multi-hop “ad hoc” networking,Carey,Kelly,17,3. IEEE 802.11b Wireless LANs,18,The Basics,In sev
13、eral respects, the IEEE 802.11b wireless LAN (WLAN) standard is similar to that for IEEE 802.3 (Ethernet) LANs Similarities: LAN; limited geographic coverage; multiple stations; shared transmission medium; CSMA-based Medium Access Control protocol; 48-bit MAC addresses; comparable data rates (11 Mbp
14、s vs 10 Mbps),19,The Basics (Contd),But there are also distinct differences: wireless (air interface) versus wired (coax) wireless propagation environment (multipath) higher error rate due to interference, etc. successful frames are ACKed by receiver mobile stations; “hidden node” problem; potential
15、 asymmetries CSMA/CA versus CSMA/CD multiple data transmission rates (1, 2, 5.5, 11),20,Some Features,Infrastructure mode vs “ad hoc” mode Access Point (AP) sends “beacon frames” Mobiles choose AP based on signal strength Multiple channel access protocols supported CSMA/CA (DCF); PCF; RTS/CTS MAC-la
16、yer can provide error control, retransmission, rate adaptation, etc. Direct Sequence Spread Spectrum (DSSS) signal spread across 14 22-MHz channels,21,Where Does Wireless RF Live? ISM Band: Industrial, Scientific, Medical,902-928 MHz,2400-2483.5 MHz,5725-5850 MHz,802.11/802.11b,802.11a,Bluetooth,Cordless Phones,Home RF,Baby Monitors,Microwave Ovens,Old Wireless,22,Where does 802.11 live in the OSI?,23,Wireless Cells,11 Mbps bandwidth “shared” by all devices in the Cell!,
