Chapter 6 outline Chapter 6: Wireless and Mobile Networks - PDF document

Chapter 6 outline Chapter 6: Wireless and Mobile Networks Background: 6.1 Introduction Mobility � # wireless (mobile) phone subscribers now � 6.5 Principles: exceeds # wired phone subscribers! addressing and routing Wireless to mobile users � computer nets: laptops, palmtops, PDAs, � 6.2 Wireless links, Internet-enabled phone promise anytime � 6.6 Mobile IP characteristics untethered Internet access � 6.7 Handling mobility in � CDMA cellular networks � two important (but different) challenges � 6.3 IEEE 802.11 wireless LANs (“wi-fi”) � 6.8 Mobility and higher- � communication over wireless link layer protocols � 6.4 Cellular Internet � handling mobile user who changes point of Access attachment to network � architecture 6.9 Summary � standards (e.g., GSM) 6: Wireless and Mobile Networks 6: Wireless and Mobile Networks 6-1 6-2 Elements of a wireless network Elements of a wireless network base station wireless hosts � typically connected to � laptop, PDA, IP phone wired network � run applications � relay - responsible � may be stationary for sending packets (non-mobile) or mobile between wired network network network and wireless � wireless does not host(s) in its “area” infrastructure infrastructure always mean mobility � e.g., cell towers 802.11 access points 6: Wireless and Mobile Networks 6: Wireless and Mobile Networks 6-3 6-4 Characteristics of selected wireless link Elements of a wireless network standards wireless link 54 Mbps 802.11{a,g} � typically used to 5-11 Mbps 802.11b .11 p-to-p link connect mobile(s) to 1 Mbps 802.15 base station � also used as backbone link 3G UMTS/WCDMA, CDMA2000 384 Kbps network 2G � multiple access 56 Kbps IS-95 CDMA, GSM infrastructure protocol coordinates link access Outdoor Mid range Long range Indoor � various data rates, outdoor outdoor transmission distance 10 – 30m 50 – 200m 200m – 4Km 5Km – 20Km 6: Wireless and Mobile Networks 6: Wireless and Mobile Networks 6-5 6-6 1

Elements of a wireless network Elements of a wireless network infrastructure mode Ad hoc mode � base station connects � no base stations mobiles into wired � nodes can only network transmit to other � handoff: mobile nodes within link changes base station coverage network providing connection � nodes organize infrastructure into wired network themselves into a network: route among themselves 6: Wireless and Mobile Networks 6: Wireless and Mobile Networks 6-7 6-8 Wireless Link Characteristics Wireless network characteristics Multiple wireless senders and receivers create Differences from wired link …. additional problems (beyond multiple access): � decreased signal strength: radio signal A B C attenuates as it propagates through matter C (path loss) � interference from other sources: standardized C’s signal A’s signal B strength wireless network frequencies (e.g., 2.4 GHz) strength A shared by other devices (e.g., phone); devices (motors) interfere as well Hidden terminal problem space � multipath propagation: radio signal reflects off Signal fading: � B, A hear each other objects ground, arriving ad destination at � B, A hear each other slightly different times � 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 …. make communication across (even a point to point) interferring at B interference at B wireless link much more “difficult” 6: Wireless and Mobile Networks 6: Wireless and Mobile Networks 6-9 6-10 Chapter 6 outline IEEE 802.11 Wireless LAN 6.1 Introduction Mobility � 802.11b � 802.11a � 6.5 Principles: � 2.4-5 GHz unlicensed � 5-6 GHz range addressing and routing radio spectrum Wireless � up to 54 Mbps to mobile users � up to 11 Mbps � 6.2 Wireless links, � 802.11g � 6.6 Mobile IP � direct sequence spread characteristics � 2.4-5 GHz range spectrum (DSSS) in � 6.7 Handling mobility in � CDMA � up to 54 Mbps physical layer cellular networks � 6.3 IEEE 802.11 � All use CSMA/CA for • all hosts use same wireless LANs (“wi-fi”) � 6.8 Mobility and higher- multiple access chipping code layer protocols � 6.4 Cellular Internet � widely deployed, using � All have base-station Access base stations and ad-hoc network � architecture 6.9 Summary versions � standards (e.g., GSM) 6: Wireless and Mobile Networks 6: Wireless and Mobile Networks 6-11 6-12 2

IEEE 802.11: multiple access 802.11 LAN architecture � avoid collisions: 2 + nodes transmitting at same time � wireless host communicates � 802.11: CSMA - sense before transmitting with base station Internet � don’t collide with ongoing transmission by other node � base station = access � 802.11: no collision detection! point (AP) � difficult to receive (sense collisions) when transmitting due � Basic Service Set (BSS) to weak received signals (fading) (aka “cell”) in infrastructure hub, switch � can’t sense all collisions in any case: hidden terminal, fading mode contains: or router AP � goal: avoid collisions: CSMA/C(ollision)A(voidance) � wireless hosts � access point (AP): base BSS 1 station A B C AP C � ad hoc mode: hosts only C’s signal A’s signal B strength strength A BSS 2 space 6: Wireless and Mobile Networks 6: Wireless and Mobile Networks 6-13 6-14 Avoiding collisions (more) IEEE 802.11 MAC Protocol: CSMA/CA 802.11 sender idea: allow sender to “reserve” channel rather than random 1 if sense channel idle for DIFS then access of data frames: avoid collisions of long data frames sender receiver transmit entire frame (no CD) � sender first transmits small request-to-send (RTS) packets to BS using CSMA 2 if sense channel busy then DIFS � RTSs may still collide with each other (but they’re short) start random backoff time � BS broadcasts clear-to-send CTS in response to RTS timer counts down while channel idle data � RTS heard by all nodes transmit when timer expires � sender transmits data frame if no ACK, increase random backoff SIFS interval, repeat 2 � other stations defer transmissions ACK 802.11 receiver Avoid data frame collisions completely - if frame received OK using small reservation packets! return ACK after SIFS (ACK needed due to hidden terminal problem) 6: Wireless and Mobile Networks 6: Wireless and Mobile Networks 6-15 6-16 802.15: personal area network Collision Avoidance: RTS-CTS exchange A B � less than 10 m diameter AP � replacement for cables RTS(B) RTS(A) (mouse, keyboard, P S reservation collision headphones) RTS(A) P radius of � ad hoc: no infrastructure M coverage ) CTS(A) � master/slaves: S ( A C T P S S P � slaves request permission to send (to master) DATA (A) � master grants requests defer � 802.15: evolved from M Master device Bluetooth specification time Slave device S A ) ACK(A) � 2.4-2.5 GHz radio band C K ( A P Parked device (inactive) � up to 721 kbps 6: Wireless and Mobile Networks 6: Wireless and Mobile Networks 6-17 6-18 3

Components of cellular network architecture Chapter 6 outline MSC � connects cells to wide area net 6.1 Introduction Mobility � manages call setup (more later!) � handles mobility (more later!) � 6.5 Principles: cell addressing and routing Wireless � covers geographical to mobile users region � 6.2 Wireless links, � base station (BS) � 6.6 Mobile IP Mobile characteristics analogous to 802.11 AP Switching � 6.7 Handling mobility in � CDMA � mobile users attach Center Public telephone cellular networks to network through BS network, and � 6.3 IEEE 802.11 Internet � air-interface: wireless LANs (“wi-fi”) � 6.8 Mobility and higher- physical and link layer layer protocols Mobile � 6.4 Cellular Internet protocol between Switching mobile and BS Access Center � architecture 6.9 Summary wired network � standards (e.g., GSM) 6: Wireless and Mobile Networks 6: Wireless and Mobile Networks 6-19 6-20 Cellular networks: the first hop Cellular standards: brief survey Two techniques for sharing 2G systems: voice channels mobile-to-BS radio � IS-136 TDMA: combined FDMA/TDMA (north spectrum america) � combined FDMA/TDMA: � GSM (global system for mobile communications): divide spectrum in time slots combined FDMA/TDMA frequency channels, divide each channel into time � most widely deployed slots � IS-95 CDMA: code division multiple access frequency � CDMA: code division bands multiple access T D M A CDMA-2000 / F D M A D G E G P R S E UMTS Don’t drown in a bowl IS-136 IS-95 GSM of alphabet soup: use this oor reference only 6: Wireless and Mobile Networks 6: Wireless and Mobile Networks 6-21 6-22 Cellular standards: brief survey Cellular standards: brief survey 2.5 G systems: voice and data channels 3G systems: voice/data � for those who can’t wait for 3G service: 2G extensions � Universal Mobile Telecommunications Service (UMTS) � general packet radio service (GPRS) � GSM next step, but using CDMA � evolved from GSM � CDMA-2000 � data sent on multiple channels (if available) � enhanced data rates for global evolution (EDGE) � also evolved from GSM, using enhanced modulation � Date rates up to 384K � CDMA-2000 (phase 1) ….. more (and more interesting) cellular topics due to � data rates up to 144K mobility (stay tuned for details) � evolved from IS-95 6: Wireless and Mobile Networks 6: Wireless and Mobile Networks 6-23 6-24 4