Wireless and Mobile Networks Wireless and 802.11 LANs • wireless links: – shared, fading, interference, hidden terminal problem • IEEE 802.11 ( “ wi-fi ” ) – CSMA/CA reflects wireless channel characteristics – DIFS, SIFS, receiver ACK, RTS/CTS, NAV, … Cellular Network Architectures (and its Evolution): an Overview • An overview of cellular network architecture • 3G and 4G LTE cellular networks Mobility • principles: addressing, routing to mobile users – home, visited networks – direct, indirect routing – care-of-addresses • case studies – mobile IP; mobility management in cellular networks Readings: Textbook, Chapter 7 CSci4211 802.11 Wireless and Mobile Networks 1
Chapter 7 outline 7.1 Introduction Mobility • 7.5 Principles: Wireless addressing and routing • 7.2 Wireless links, to mobile users characteristics • 7.6 Mobile IP – CDMA • 7.7 Handling mobility in • 7.3 IEEE 802.11 cellular networks wireless LANs ( “ wi- • 7.8 Mobility and higher- fi ” ) layer protocols • 7.4 Cellular Internet Access 7.9 Summary – architecture – standards (e.g., GSM) CSci4211 802.11 Wireless and Mobile Networks 2
Elements of a Wireless Network wireless hosts • laptop, PDA, IP phone • run applications • may be stationary (non-mobile) or mobile network – wireless does not always infrastructure mean mobility CSci4211 802.11 Wireless and Mobile Networks 3
Elements of a Wireless Network base station • typically connected to wired network • relay - responsible for sending packets between wired network network and wireless infrastructure host(s) in its “ area ” – e.g., cell towers 802.11 access points CSci4211 802.11 Wireless and Mobile Networks 4
Elements of a Wireless Network wireless link • typically used to connect mobile(s) to base station • also used as backbone link network • multiple access infrastructure protocol coordinates link access • various data rates, transmission distance CSci4211 802.11 Wireless and Mobile Networks 5
Characteristics of selected wireless links 1300 802.11 ac 450 802.11n Data rate (Mbps) 54 802.11a,g 802.11a,g point-to-point 5-11 802.11b 4G: LTWE WIMAX 4 3G: UMTS/WCDMA-HSPDA, CDMA2000-1xEVDO 1 802.15 .384 2.5G: UMTS/WCDMA, CDMA2000 .056 2G: IS-95, CDMA, GSM Outdoor Indoor Mid-range outdoor Long-range outdoor 50-200m 10-30m 200m – 4 Km 5Km – 20 Km CSci4211 802.11 Wireless and Mobile Networks 6
Wireless Link Characteristics (1) Differences from wired link …. – decreased signal strength: radio signal attenuates as it propagates through matter (path loss) – interference from other sources: standardized wireless network frequencies (e.g., 2.4 GHz) shared by other devices (e.g., phone); devices (motors) interfere as well – multipath propagation: radio signal reflects off objects ground, arriving ad destination at slightly different times …. make communication across (even a point to point) wireless link much more “ difficult ” CSci4211 802.11 Wireless and Mobile Networks 7
Wireless Link Characteristics (2) • SNR: signal-to-noise ratio 10 -1 – larger SNR – easier to 10 -2 extract signal from noise (a 10 -3 “ good thing ” ) BER 10 -4 • SNR versus BER tradeoffs 10 -5 – given physical layer: increase power -> increase SNR- 10 -6 >decrease BER 10 -7 – given SNR: choose physical layer 10 20 30 40 that meets BER requirement, SNR(dB) giving highest thruput QAM256 (8 Mbps) • SNR may change with mobility: QAM16 (4 Mbps) dynamically adapt physical layer (modulation technique, rate) BPSK (1 Mbps) CSci4211 802.11 Wireless and Mobile Networks 8
Wireless Network Characteristics Multiple wireless senders and receivers create additional problems (beyond multiple access): A B C C C ’ s signal A ’ s signal strength B strength A Hidden terminal problem space Signal attenuation: § B, A hear each other § B, A hear each other § B, C hear each other § B, C hear each other § A, C can not hear each other § A, C can not hear each other means A, C unaware of their interfering at B interference at B CSci4211 802.11 Wireless and Mobile Networks 9
Optional: A Brief Intro to Code Division Multiple Access (CDMA) • unique “ code ” assigned to each user; i.e., code set partitioning – all users share same frequency, but each user has own “ chipping ” sequence (i.e., code) to encode data – allows multiple users to “ coexist ” and transmit simultaneously with minimal interference (if codes are “ orthogonal ” ) • encoded signal = (original data) X (chipping sequence) • decoding: inner-product of encoded signal and chipping sequence CSci4211 802.11 Wireless and Mobile Networks 10
CDMA Encode/Decode channel output Z i,m Z i,m = d i. c m data d 0 = 1 1 1 1 1 1 1 1 1 d 1 = -1 bits - 1 - 1 - 1 - 1 - 1 - 1 - 1 - 1 sender slot 0 slot 1 1 1 1 1 1 1 1 1 code channel channel - - 1 - 1 - 1 1 - - - - 1 1 1 1 output output slot 1 slot 0 M D i = S Z i,m. c m m=1 M received 1 1 1 1 1 1 1 1 d 0 = 1 - - - 1 - - - - - 1 1 1 1 1 1 1 d 1 = -1 input slot 0 slot 1 1 1 1 1 1 1 1 1 code channel channel - - 1 - 1 - 1 1 - 1 - 1 - 1 - 1 output output receiver slot 1 slot 0 CSci4211 802.11 Wireless and Mobile Networks 11
CDMA: Two-sender Interference channel sums together transmissions by sender 1 and 2 Sender 1 Sender 2 using same code as sender 1, receiver recovers sender 1’s original data from summed channel data! CSci4211 802.11 Wireless and Mobile Networks 12
Back to Wireless Networks: A Taxonomy multiple hops single hop host may have to host connects to relay through several infrastructure base station (WiFi, wireless nodes to (e.g., APs) WiMAX, cellular) connect to larger which connects to Internet: mesh net larger Internet no base station, no connection to larger no no base station, no Internet. May have to connection to larger infrastructure relay to reach other Internet (Bluetooth, a given wireless node ad hoc nets) MANET, VANET CSci4211 802.11 Wireless and Mobile Networks 13
Elements of a Wireless Network infrastructure mode • base station connects mobiles into wired network • handoff: mobile changes base station network providing connection infrastructure into wired network CSci4211 802.11 Wireless and Mobile Networks 14
Elements of a Wireless Network Ad hoc mode • no base stations • nodes can only transmit to other nodes within link coverage • nodes organize themselves into a network: route among themselves CSci4211 802.11 Wireless and Mobile Networks 15
IEEE 802.11 Wireless LAN • 802.11g • 802.11b – 2.4-5 GHz range – 2.4-5 GHz unlicensed – up to 54 Mbps radio spectrum • 802.11n – up to 11 Mbps – MIMO, 20/40MHz channels in 2.4 GHz – direct sequence spread spectrum (DSSS) in – up to 600 Mbps physical layer • 802.11ac • all hosts use same – wider RF band per station (80/160 MHz), chipping code more MIMO, multi-user MIMO, 5 GHz – widely deployed, using - at least 1 Gbps total, 500 Mbps per link base stations • 802.11a • All use CSMA/CA for multiple access – 5-6 GHz range • All have base-station and ad-hoc – up to 54 Mbps network versions CSci4211 802.11 Wireless and Mobile Networks 16
802.11 LAN Infrastructure Mode • wireless host communicates Internet with base station – base station = access point (AP) • Basic Service Set (BSS) hub, switch (aka “ cell ” ) in or router AP infrastructure mode contains: BSS 1 – wireless hosts AP – access point (AP): base station – ad hoc mode: hosts only BSS 2 CSci4211 802.11 Wireless and Mobile Networks 17
802.11: Channels, Association • 802.11b: 2.4GHz-2.485GHz spectrum divided into 11 channels at different frequencies – AP admin chooses frequency for AP – interference possible: channel can be same as that chosen by neighboring AP! • host: must associate with an AP – scans channels, listening for beacon frames containing AP ’ s name (SSID) and MAC address – selects AP to associate with – may perform authentication [Chapter 8] – will typically run DHCP to get IP address in AP ’ s subnet CSci4211 802.11 Wireless and Mobile Networks 18
802.11: Passive/Active scanning BBS 1 BBS 2 BBS 1 BBS 2 1 AP 2 2 2 AP 1 1 1 3 AP 1 AP 2 4 2 3 H1 H1 active scanning : (1) Probe Request frame broadcast passive scanning: from H1 (1) beacon frames sent from APs (2) Probe Response frames sent (2) association Request frame sent: from APs H1 to selected AP (3) Association Request frame sent: (3) association Response frame sent H1 to selected AP from selected AP to H1 (4) Association Response frame sent from selected AP to H1 CSci4211 802.11 Wireless and Mobile Networks 19
Ad Hoc Network Approach • No access point (i.e., base station) – “ peer-to-peer ” mode • wireless hosts communicate with each other – to get packet from wireless host A to B may need to route through wireless hosts X,Y,Z • Applications: – “ laptop ” meeting in conference room, car – interconnection of “ personal ” devices – battlefield • IETF MANET (Mobile Ad hoc Networks) working group CSci4211 802.11 Wireless and Mobile Networks 20
Recommend
More recommend
