Wireless and Mobility 6 Wireless and Mobile Networks

Wireless and Mobility 6: Wireless and Mobile Networks 1

Chapter 6: Wireless and Mobile Networks Background: r # wireless (mobile) phone subscribers now exceeds # wired phone subscribers! r computer nets: laptops, palmtops, PDAs, Internet-enabled phone promise anytime untethered Internet access r two important (but different) challenges m m communication over wireless link handling mobile user who changes point of attachment to network 6: Wireless and Mobile Networks 2

Internet expansion 6: Wireless and Mobile Networks 3

Future Applications 6: Wireless and Mobile Networks 4

6: Wireless and Mobile Networks 5

6: Wireless and Mobile Networks 6

Chapter 6 outline 6. 1 Introduction Wireless r 6. 2 Wireless links, characteristics m CDMA r 6. 3 IEEE 802. 11 wireless LANs (“wi-fi”) r 6. 4 Cellular Internet Access m m architecture standards (e. g. , GSM) Mobility r 6. 5 Principles: addressing and routing to mobile users r 6. 6 Mobile IP r 6. 7 Handling mobility in cellular networks r 6. 8 Mobility and higherlayer protocols 6. 9 Summary 6: Wireless and Mobile Networks 7

Elements of a wireless network infrastructure wireless hosts r laptop, PDA, IP phone r run applications r may be stationary (nonmobile) or mobile m wireless does not always mean mobility 6: Wireless and Mobile Networks 8

Elements of a wireless network infrastructure base station r typically connected to wired network r relay - responsible for sending packets between wired network and wireless host(s) in its “area” m e. g. , cell towers 802. 11 access points 6: Wireless and Mobile Networks 9

Elements of a wireless network infrastructure wireless link r typically used to connect mobile(s) to base station r also used as backbone link r multiple access protocol coordinates link access r various data rates, transmission distance 6: Wireless and Mobile Networks 10

Elements of a wireless network infrastructure mode r base station connects mobiles into wired network r handoff: mobile changes base station providing connection into wired network 6: Wireless and Mobile Networks 11

Elements of a wireless network Ad hoc mode r no base stations r nodes can only transmit to other nodes within link coverage r nodes organize themselves into a network: route among themselves 6: Wireless and Mobile Networks 12

Wireless Link Characteristics Differences from wired link …. m decreased signal strength: radio signal attenuates as it propagates through matter (path loss) m 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 m 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” 6: Wireless and Mobile Networks 13

Wireless network characteristics Multiple wireless senders and receivers create additional problems (beyond multiple access): C A B Hidden terminal problem C C’s signal strength A’s signal strength space r B, A hear each other Signal fading: r A, C can not hear each other r B, C hear each other r B, A hear each other means A, C unaware of their interference at B r A, C can not hear each other interferring at B 6: Wireless and Mobile Networks 14

Code Division Multiple Access (CDMA) r used in several wireless broadcast channels r r r (cellular, satellite, etc) standards 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 encoded signal = (original data) X (chipping sequence) decoding: inner-product of encoded signal and chipping sequence allows multiple users to “coexist” and transmit simultaneously with minimal interference (if codes are “orthogonal”) 6: Wireless and Mobile Networks 15

CDMA Encode/Decode sender data bits code Zi, m= di. cm d 0 = 1 -1 -1 -1 1 1 1 -1 -1 -1 slot 1 channel output 1 -1 1 1 1 d 1 = -1 1 channel output Zi, m -1 -1 -1 slot 0 channel output M Di = S Zi, m. cm m=1 received input code receiver 1 1 1 1 -1 -1 -1 1 -1 -1 -1 slot 1 M 1 1 -1 -1 slot 0 d 0 = 1 d 1 = -1 slot 1 channel output slot 0 channel output 6: Wireless and Mobile Networks 16

CDMA’s Evolution 1 x. EV Phase 1 (1 x. EV-DO) cdma 2000 1 X IS-95 -A • Voice • 14. 4 kbps • High Capacity Voice • 153 kbps Packet • RF Backward Comp. • 2. 4 Mbps Packet • RF Backward Comp. ？ 1 x. EV Phase 2 (1 x. EV-DV) • Higher Cap Voice/ Data • RF Backward Comp. cdma 2000 3 X MC • High Capacity Voice • 384+ kbps Packet • RF Backward Comp. 1995 1999 2000 2001 2002 2003+ 6: Wireless and Mobile Networks 17

Chapter 6 outline 6. 1 Introduction Wireless r 6. 2 Wireless links, characteristics m CDMA r 6. 3 IEEE 802. 11 wireless LANs (“wi-fi”) r 6. 4 Cellular Internet Access m m architecture standards (e. g. , GSM) Mobility r 6. 5 Principles: addressing and routing to mobile users r 6. 6 Mobile IP r 6. 7 Handling mobility in cellular networks r 6. 8 Mobility and higherlayer protocols 6. 9 Summary 6: Wireless and Mobile Networks 18

IEEE 802. 11 Wireless LAN r 802. 11 b m 2. 4 -5 GHz unlicensed radio spectrum m up to 11 Mbps m direct sequence spread spectrum (DSSS) in physical layer • all hosts use same chipping code m widely deployed, using base stations r 802. 11 a m 5 -6 GHz range m up to 54 Mbps r 802. 11 g m 2. 4 -5 GHz range m up to 54 Mbps r All use CSMA/CA for multiple access r All have base-station and ad-hoc network versions 6: Wireless and Mobile Networks 19

802. 11 LAN architecture r wireless host communicates Internet AP hub, switch or router BSS 1 AP BSS 2 with base station m base station = access point (AP) r Basic Service Set (BSS) (aka “cell”) in infrastructure mode contains: m wireless hosts m access point (AP): base station m ad hoc mode: hosts only 6: Wireless and Mobile Networks 20

802. 11: Channels, association r 802. 11 b: 2. 4 GHz-2. 485 GHz spectrum divided into 11 channels at different frequencies m AP admin chooses frequency for AP m interference possible: channel can be same as that chosen by neighboring AP! r host: must associate with an AP m scans channels, listening for beacon frames containing AP’s name (SSID) and MAC address m selects AP to associate with m may perform authentication [Chapter 8] m will typically run DHCP to get IP address in AP’s subnet 6: Wireless and Mobile Networks 21

IEEE 802. 11: multiple access r avoid collisions: 2+ nodes transmitting at same time r 802. 11: CSMA - sense before transmitting m don’t collide with ongoing transmission by other node r 802. 11: no collision detection! m difficult to receive (sense collisions) when transmitting due to weak received signals (fading) m can’t sense all collisions in any case: hidden terminal, fading m goal: avoid collisions: CSMA/C(ollision)A(voidance) C A B C C’s signal strength A’s signal strength space 6: Wireless and Mobile Networks 22

IEEE 802. 11 MAC Protocol: CSMA/CA 802. 11 sender 1 if sense channel idle for DIFS then transmit entire frame (no CD) 2 if sense channel busy then start random backoff timer counts down while channel idle transmit when timer expires if no ACK, increase random backoff interval, repeat 2 sender receiver DIFS data SIFS ACK 802. 11 receiver - if frame received OK return ACK after SIFS (ACK needed due to hidden terminal problem) 6: Wireless and Mobile Networks 23

Avoiding collisions (more) idea: allow sender to “reserve” channel rather than random access of data frames: avoid collisions of long data frames r sender first transmits small request-to-send (RTS) packets to BS using CSMA m RTSs may still collide with each other (but they’re short) r BS broadcasts clear-to-send CTS in response to RTS r RTS heard by all nodes m sender transmits data frame m other stations defer transmissions Avoid data frame collisions completely using small reservation packets! 6: Wireless and Mobile Networks 24

Collision Avoidance: RTS-CTS exchange A B AP RTS(B) RTS(A) reservation collision RTS(A) CTS(A) DATA (A) time ACK(A) defer ACK(A) 6: Wireless and Mobile Networks 25

802. 11: mobility within same subnet r H 1 remains in same IP subnet: IP address can remain same r switch: which AP is associated with H 1? m self-learning (Ch. 5): switch will see frame from H 1 and “remember” which switch port can be used to reach H 1 router hub or switch BBS 1 AP 2 H 1 BBS 2 6: Wireless and Mobile Networks 26

802. 15: personal area network r less than 10 m diameter r replacement for cables (mouse, keyboard, headphones) r ad hoc: no infrastructure r master/slaves: m m slaves request permission to send (to master) master grants requests r 802. 15: evolved from Bluetooth specification m m 2. 4 -2. 5 GHz radio band up to 721 kbps P S P radius of coverage M S P M Master device S Slave device P Parked device (inactive) 6: Wireless and Mobile Networks 27

Chapter 6 outline 6. 1 Introduction Wireless r 6. 2 Wireless links, characteristics m CDMA r 6. 3 IEEE 802. 11 wireless LANs (“wi-fi”) r 6. 4 Cellular Internet Access m m architecture standards (e. g. , GSM) Mobility r 6. 5 Principles: addressing and routing to mobile users r 6. 6 Mobile IP r 6. 7 Handling mobility in cellular networks r 6. 8 Mobility and higherlayer protocols 6. 9 Summary 6: Wireless and Mobile Networks 28

Components of cellular network architecture MSC cell q connects cells to wide area net q manages call setup (more later!) q handles mobility (more later!) q covers geographical region q base station (BS) analogous to 802. 11 AP q mobile users attach to network through BS q air-interface: physical and link layer protocol between mobile and BS Mobile Switching Center Public telephone network, and Internet Mobile Switching Center wired network 6: Wireless and Mobile Networks 29

Cellular networks: the first hop Two techniques for sharing mobile-to-BS radio spectrum r combined FDMA/TDMA: divide spectrum in frequency channels, divide each channel into time slots frequency bands r CDMA: code division multiple access time slots 6: Wireless and Mobile Networks 30

Cellular standards: brief survey 2 G systems: voice channels r IS-136 TDMA: combined FDMA/TDMA (north america) r GSM (global system for mobile communications): combined FDMA/TDMA m most widely deployed r IS-95 CDMA: code division multiple access TDMA/FDMA 0 CDMA-200 GPRS EDGE UMTS IS-136 GSM IS-95 Don’t drown in a bowl of alphabet soup: use this oor reference only 6: Wireless and Mobile Networks 31

Cellular standards: brief survey 2. 5 G systems: voice and data channels r for those who can’t wait for 3 G service: 2 G extensions r general packet radio service (GPRS) m evolved from GSM m data sent on multiple channels (if available) r enhanced data rates for global evolution (EDGE) m also evolved from GSM, using enhanced modulation m Date rates up to 384 K r CDMA-2000 (phase 1) m data rates up to 144 K m evolved from IS-95 6: Wireless and Mobile Networks 32

GPRS or CDMA? 2 G 2 G++ 3 G North America IS-95 A IS-95 B IS-95 C CDMA 2000 Europe GSM TDMA GSM+ GPRS, HSCSD GSM++ EDGE WCDMA 6: Wireless and Mobile Networks 33

Cellular standards: brief survey 3 G systems: voice/data r Universal Mobile Telecommunications Service (UMTS) m GSM next step, but using CDMA r CDMA-2000 …. . more (and more interesting) cellular topics due to mobility (stay tuned for details) 6: Wireless and Mobile Networks 34

Chapter 6 outline 6. 1 Introduction Wireless r 6. 2 Wireless links, characteristics m CDMA r 6. 3 IEEE 802. 11 wireless LANs (“wi-fi”) r 6. 4 Cellular Internet Access m m architecture standards (e. g. , GSM) Mobility r 6. 5 Principles: addressing and routing to mobile users r 6. 6 Mobile IP r 6. 7 Handling mobility in cellular networks r 6. 8 Mobility and higherlayer protocols 6. 9 Summary 6: Wireless and Mobile Networks 35

What is mobility? r spectrum of mobility, from the network perspective: no mobility high mobility mobile wireless user, mobile user, using same access connecting/ point disconnecting from network using DHCP. mobile user, passing through multiple access point while maintaining ongoing connections (like cell phone) 6: Wireless and Mobile Networks 36

Mobility: Vocabulary home network: permanent “home” of mobile (e. g. , 128. 119. 40/24) Permanent address: address in home network, can always be used to reach mobile e. g. , 128. 119. 40. 186 home agent: entity that will perform mobility functions on behalf of mobile, when mobile is remote wide area network correspondent 6: Wireless and Mobile Networks 37

Mobility: more vocabulary Permanent address: remains constant (e. g. , 128. 119. 40. 186) visited network: network in which mobile currently resides (e. g. , 79. 129. 13/24) Care-of-address: address in visited network. (e. g. , 79, 129. 13. 2) wide area network correspondent: wants to communicate with mobile home agent: entity in visited network that performs mobility functions on behalf of mobile. 6: Wireless and Mobile Networks 38

How do you contact a mobile friend: Consider friend frequently changing addresses, how do you find her? I wonder where Alice moved to? r search all phone books? r call her parents? r expect her to let you know where he/she is? 6: Wireless and Mobile Networks 39

Mobility: approaches r Let routing handle it: routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange. m routing tables indicate where each mobile located m no changes to end-systems r Let end-systems handle it: m indirect routing: communication from correspondent to mobile goes through home agent, then forwarded to remote m direct routing: correspondent gets foreign address of mobile, sends directly to mobile 6: Wireless and Mobile Networks 40

Mobility: approaches r Let routing handle it: routers advertise permanent not address of mobile-nodes-in-residence via usual scalable routing table exchange. to millions of m routing tables indicate mobiles where each mobile located m no changes to end-systems r let end-systems handle it: m indirect routing: communication from correspondent to mobile goes through home agent, then forwarded to remote m direct routing: correspondent gets foreign address of mobile, sends directly to mobile 6: Wireless and Mobile Networks 41

Mobility: registration visited network home network 1 2 wide area network foreign agent contacts home agent home: “this mobile is resident in my network” mobile contacts foreign agent on entering visited network End result: r Foreign agent knows about mobile r Home agent knows location of mobile 6: Wireless and Mobile Networks 42

Mobility via Indirect Routing foreign agent receives packets, forwards to mobile home agent intercepts packets, forwards to foreign agent home network visited network 3 wide area network correspondent addresses packets using home address of mobile 1 2 4 mobile replies directly to correspondent 6: Wireless and Mobile Networks 43

Indirect Routing: comments r Mobile uses two addresses: m permanent address: used by correspondent (hence mobile location is transparent to correspondent) m care-of-address: used by home agent to forward datagrams to mobile r foreign agent functions may be done by mobile itself r triangle routing: correspondent-home-networkmobile m inefficient when correspondent, mobile are in same network 6: Wireless and Mobile Networks 44

Indirect Routing: moving between networks r suppose mobile user moves to another network m registers with new foreign agent m new foreign agent registers with home agent m home agent update care-of-address for mobile m packets continue to be forwarded to mobile (but with new care-of-address) r mobility, changing foreign networks transparent: on going connections can be maintained! 6: Wireless and Mobile Networks 45

Mobility via Direct Routing correspondent forwards to foreign agent receives packets, forwards to mobile home network 4 wide area network 2 correspondent requests, receives foreign address of mobile visited network 1 3 4 mobile replies directly to correspondent 6: Wireless and Mobile Networks 46

Mobility via Direct Routing: comments r overcome triangle routing problem r non-transparent to correspondent: correspondent must get care-of-address from home agent m what if mobile changes visited network? 6: Wireless and Mobile Networks 47

Accommodating mobility with direct routing r anchor foreign agent: FA in first visited network r data always routed first to anchor FA r when mobile moves: new FA arranges to have data forwarded from old FA (chaining) foreign net visited at session start wide area network anchor foreign agent 1 2 4 5 correspondent agent 3 new foreign agent new foreign network 6: Wireless and Mobile Networks 48

Chapter 6 outline 6. 1 Introduction Wireless r 6. 2 Wireless links, characteristics m CDMA r 6. 3 IEEE 802. 11 wireless LANs (“wi-fi”) r 6. 4 Cellular Internet Access m m architecture standards (e. g. , GSM) Mobility r 6. 5 Principles: addressing and routing to mobile users r 6. 6 Mobile IP r 6. 7 Handling mobility in cellular networks r 6. 8 Mobility and higherlayer protocols 6. 9 Summary 6: Wireless and Mobile Networks 49

Mobile IP r RFC 3220 r has many features we’ve seen: m home agents, foreign-agent registration, care-of-addresses, encapsulation (packet-within-a-packet) r three components to standard: m indirect routing of datagrams m agent discovery m registration with home agent 6: Wireless and Mobile Networks 50

Mobile IP: indirect routing foreign-agent-to-mobile packet sent by home agent to foreign agent: a packet within a packet dest: 79. 129. 13. 2 dest: 128. 119. 40. 186 Permanent address: 128. 119. 40. 186 dest: 128. 119. 40. 186 Care-of address: 79. 129. 13. 2 packet sent by correspondent 6: Wireless and Mobile Networks 51

Handling mobility in cellular networks r home network: network of cellular provider you subscribe to (e. g. , Sprint PCS, Verizon) m home location register (HLR): database in home network containing permanent cell phone #, profile information (services, preferences, billing), information about current location (could be in another network) r visited network: network in which mobile currently resides m visitor location register (VLR): database with entry for each user currently in network m could be home network 6: Wireless and Mobile Networks 52

GSM: indirect routing to mobile home network HLR 2 home MSC consults HLR, gets roaming number of mobile in visited network correspondent home Mobile Switching Center 1 VLR 3 Mobile Switching Center 4 Public switched telephone network call routed to home network home MSC sets up 2 nd leg of call to MSC in visited network mobile user visited network MSC in visited network completes call through base station to mobile 6: Wireless and Mobile Networks 53

Chapter 6 Summary Wireless r wireless links: m m m capacity, distance channel impairments CDMA r IEEE 802. 11 (“wi-fi”) m CSMA/CA reflects wireless channel characteristics r cellular access m architecture m standards (e. g. , GSM, CDMA-2000, UMTS) Mobility r principles: addressing, routing to mobile users m m m home, visited networks direct, indirect routing care-of-addresses r case studies m mobile IP m mobility in GSM r impact on higher-layer protocols 6: Wireless and Mobile Networks 54