Chapter 6 Wireless and Mobile Networks Computer Networking

Chapter 6 Wireless and Mobile Networks Computer Networking: A Top Down Approach 5 th edition. Jim Kurose, Keith Ross Addison-Wesley, April 2009. Computer Networking: A Top Down Approach 4 th edition. Jim Kurose, Keith Ross Addison-Wesley, July 2007. 6: Wireless and Mobile Networks 6 -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 wireless: communication over wireless link mobility: handling the mobile user who changes point of attachment to network 6: Wireless and Mobile Networks 6 -2

Chapter 6 outline 6. 1 Introduction Wireless r 6. 2 Wireless links, characteristics 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 6 -3

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 6 -4

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 6 -5

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 6 -6

Characteristics of selected wireless link standards Data rate (Mbps) 200 54 5 -11 802. 11 n 802. 11 a, g 802. 11 b 4 1 802. 11 a, g point-to-point data 802. 16 (Wi. MAX) UMTS/WCDMA-HSPDA, CDMA 2000 -1 x. EVDO 3 G cellular enhanced 802. 15 . 384 3 G UMTS/WCDMA, CDMA 2000 . 056 2 G IS-95, CDMA, GSM Indoor Outdoor 10 -30 m 50 -200 m Mid-range outdoor Long-range outdoor 200 m – 4 Km 5 Km – 20 Km 6: Wireless and Mobile Networks 6 -7

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 6 -8

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 6 -9

Wireless network taxonomy single hop infrastructure (e. g. , APs) no infrastructure host connects to base station (Wi. Fi, Wi. MAX, cellular) which connects to larger Internet no base station, no connection to larger Internet (Bluetooth, ad hoc nets) Mobile Adhoc Networks multiple hops host may have to relay through several wireless nodes to connect to larger Internet: mesh net no base station, no connection to larger Internet. May have to relay to reach other a given wireless node MANET, VANET Vehicular Adhoc Networks 6: Wireless and Mobile Networks 6 -10

Wireless Communication Systems & Networking - What complicates wireless networking vs. wired networking? 6: Wireless and Mobile Networks 6 -11

- 1 - Channel characteristics - for satellite we get extended propagation delays - high bit error rate ‘BER’ (higher than optical fiber and coax. ) - asymmetry in bandwidth and delay - unidirectional links - effects of wave propagation, attenuation, … etc. - 2 - Mobility: continuous and introduces topology dynamics - 3 - Power constraints in lots of the wireless devices 6: Wireless and Mobile Networks 6 -12

Wireless Link Characteristics (1) 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 6 -13

Wireless Link Characteristics (2) 10 -1 r SNR: signal-to-noise ratio larger SNR – easier to extract signal from noise (a “good thing”) r SNR versus BER tradeoffs m given physical layer: increase power -> increase SNR->decrease BER m given SNR: choose physical layer that meets BER requirement, giving highest thruput 10 -2 m • SNR may change with mobility: dynamically adapt physical layer (modulation technique, rate) BER 10 -3 10 -4 10 -5 10 -6 10 -7 10 20 30 40 SNR(d. B) QAM 256 (8 Mbps) QAM 16 (4 Mbps) BPSK (1 Mbps) Quadrature Amplitude Modulation (QAM) Binary Phase Shift Keying (BPSK) 6: Wireless and Mobile Networks 6 -14

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 attenuation: 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 interfering at B 6: Wireless and Mobile Networks 6 -15

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 6 -16

IEEE 802. 11 Wireless LAN r 802. 11 a r 802. 11 b m 5 -6 GHz range m 2. 4 -5 GHz unlicensed spectrum m up to 54 Mbps m up to 11 Mbps r 802. 11 g m direct sequence spread spectrum (DSSS) in physical m 2. 4 -5 GHz range layer (CDMA: code division m up to 54 Mbps multiple access) r 802. 11 n: multiple antennae • all hosts use same chipping m 2. 4 -5 GHz range code m up to 200 Mbps r all use CSMA/CA for multiple access r all have base-station and ad-hoc network versions 6: Wireless and Mobile Networks 6 -17

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 6 -18

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 service set ID (SSID) and MAC address m selects AP to associate with m may perform authentication m will typically run DHCP to get IP address in AP’s subnet 6: Wireless and Mobile Networks 6 -19

802. 11: passive/active scanning BBS 1 AP 1 BBS 2 1 1 2 AP 2 BBS 1 AP 1 BBS 2 1 2 3 (1) beacon frames sent from APs (2) association Request frame sent: H 1 to selected AP (3) association Response frame sent: selected AP to H 1 AP 2 4 H 1 Passive Scanning: 2 3 Active Scanning: (1) Probe Request frame broadcast from H 1 (2) Probes response frame sent from APs (3) Association Request frame sent: H 1 to selected AP (4) Association Response frame sent: selected AP to H 1 6: Wireless and Mobile Networks 6 -20

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 6 -21

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 2 802. 11 receiver - if frame received OK return ACK after SIFS (ACK needed due to hidden terminal problem) sender receiver DIFS data SIFS ACK Distributed Inter-frame Spacing (DIFS) Short Inter-frame Spacing (SIFS) 6: Wireless and Mobile Networks 6 -22

Hidden Terminal Problem in WLANs 6: Wireless and Mobile Networks 6 -23

Avoiding collisions: RTS/CTS 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 6 -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 6 -25

Check Animations on-line (applet & ns) 6: Wireless and Mobile Networks 6 -26

802. 11 frame: addressing 2 2 6 6 6 frame address duration control 1 2 3 Address 1: MAC address of wireless host or AP to receive this frame 2 6 seq address 4 control 0 - 2312 4 payload CRC Address 4: used only in ad hoc mode Address 3: MAC address of router interface to which AP is attached Address 2: MAC address of wireless host or AP transmitting this frame 6: Wireless and Mobile Networks 6 -27

802. 11 frame: addressing R 1 router H 1 Internet AP R 1 MAC addr AP MAC addr dest. address source address 802. 3 frame AP MAC addr H 1 MAC addr R 1 MAC address 1 address 2 address 3 802. 11 frame 6: Wireless and Mobile Networks 6 -28

802. 11 frame: more frame seq # (for reliable ARQ) duration of reserved transmission time (RTS/CTS) 2 2 6 6 6 frame address duration control 1 2 3 2 Protocol version 2 4 1 Type Subtype To AP 6 2 1 seq address 4 control 1 From More AP frag 1 Retry 1 0 - 2312 4 payload CRC 1 Power More mgt data 1 1 WEP Rsvd frame type (RTS, CTS, ACK, data) 6: Wireless and Mobile Networks 6 -29

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 6 -30

802. 11: advanced capabilities QAM 256 (8 Mbps) QAM 16 (4 Mbps) BPSK (1 Mbps) operating point Rate adaptation can change rate from 100 Mbps to 1 Mbps !! Does this affect higher protocol layers? 10 -1 10 -2 10 -3 BER Rate Adaptation r base station, mobile dynamically change transmission rate (physical layer modulation technique) as mobile moves, SNR varies 10 -4 10 -5 10 -6 10 -7 10 20 30 SNR(d. B) 40 1. SNR decreases, BER increase as node moves away from base station 2. When BER becomes too high, switch to lower transmission rate but with lower BER 6: Wireless and Mobile Networks 6 -31

802. 11: advanced capabilities Power Management r node-to-AP: “I am going to sleep until next beacon frame” m. AP knows not to transmit frames to this node mnode wakes up before next beacon frame r beacon frame: contains list of mobiles with APto-mobile frames waiting to be sent mnode will stay awake if AP-to-mobile frames to be sent; otherwise sleep again until next beacon frame (typically after 100 msec) 6: Wireless and Mobile Networks 6 -32

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 6 -33

802. 16: Wi. MAX r like 802. 11 & cellular: point-to-point base station model m transmissions to/from base station by hosts with omnidirectional antenna m base station-to-base station backhaul with point-to-point antenna point-to-multipoint r unlike 802. 11: m range ~ 6 miles (“city rather than coffee shop”) m ~14 Mbps 6: Wireless and Mobile Networks 6 -34

802. 16: Wi. MAX: downlink, uplink scheduling r transmission frame m down-link subframe: base station to node m uplink subframe: node to base station pream. … DL- ULMAP DL burst 1 DL burst 2 downlink subframe … … DL burst n Initial request SS #1 SS #2 maint. conn. … SS #k uplink subframe base station tells nodes who will get to receive (DL map) and who will get to send (UL map), and when r Wi. MAX standard provide mechanism for scheduling, but not scheduling algorithm 6: Wireless and Mobile Networks 6 -35

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 6 -36

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 6 -37

Wireless Comm. Systems - In general a wireless communication network consists of: - 1 - Users (mobile station) - 2 - Base Station (BS): connects users to MSC - 3 - Mobile Switching Center (MSC): - connects the base stations with each other, and to the PSTN (public switched telephone network) 6: Wireless and Mobile Networks 6 -38

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Cellular Comm. /Networking Terminology - Hand-off: the process of transferring the mobile from one base station to another - Roamer: a mobile operating in a coverage area other than the one in which it subscribed (moving to another MSC) 6: Wireless and Mobile Networks 6 -41

Cellular Telephone Systems - A cellular system services a large number of users over extended geographical coverage with limited frequency spectrum. - High capacity is attained by limiting the coverage of the base station to a cell, so that the same frequency can be re-used in other cells - A problem may occur when moving from one cell to another while keeping the call uninterrupted. [the hand-off problem] 6: Wireless and Mobile Networks 6 -42

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Design concepts: The Cellular Concept and Frequency Re-use - The cellular concept was introduced to solve the problem of frequency limitation (or spectral congestion) and user capacity - Replace a single high power base station with several lower power base stations, each covering a smaller geographical area, a ‘cell’. - Each of the base stations is allocated a number of channels (portion of the overall system channels) 6: Wireless and Mobile Networks 6 -44

- Neighboring base stations (would in general) use different frequency channels to reduce interference. - (more later on interference, channel assignment and frequency planning) 6: Wireless and Mobile Networks 6 -45

Frequency Re-use - A cell uses a set of frequencies - A ‘cluster’ holds several cells - Frequency re-use factor: 1/#cells per cluster 6: Wireless and Mobile Networks 6 -46

B G B C G A F D E C A F B G D E G E A B D C F Cluster Cell D E C A F D E Cellular frequency re-use concept: cells with the same letter use the same set of frequencies. A cluster of cells (highlighted in bold) is replicated over the coverage area. The cluster size, N, is equal to 7. Since each cell contains one-seventh of the overall channels, the cell frequency re-use factor is 1/7. This requires channel/frequency planning and allocation! 6: Wireless and Mobile Networks 6 -47

Multiple Access (MA) Techniques for Wireless Communications - MA schemes allow multiple mobile users to share a limited frequency spectrum. - Main MA schemes: FDMA, TDMA, SSMA (FHMA, CDMA [DSMA]), SDMA 6: Wireless and Mobile Networks 6 -48

FDMA 6: Wireless and Mobile Networks 6 -49

Frequency Division Multiple Access (FDMA) - Assigns individual channels to individual - - users on demand Only 1 user utilizes the channel at a time. Idle times are wasted. Capacity is not shared. Communication is continuous Does not need synchronization Costly filters at the base station Need guard bands to alleviate interference 6: Wireless and Mobile Networks 6 -50

TDMA 6: Wireless and Mobile Networks 6 -51

Time Division Multiple Access (TDMA) - In a time slot only 1 user transmits (or - receives) Several users share a single frequency channel Transmission is non-continuous Power consumption is lower than FDMA (e. g. , the transmitter can be turned off when idle) During idle time, a mobile performs MAHO Synchronization is needed 6: Wireless and Mobile Networks 6 -52

Spread Spectrum Multiple Access (SSMA) - Traditional communication techniques - Strive to conserve bandwidth - By contrast, Spread spectrum techniques - use bandwidth several orders of magnitude larger than the min. required bandwidth !! 6: Wireless and Mobile Networks 6 -53

Spread Spectrum Multiple Access (SSMA) - Spread spectrum techniques use bandwidth larger than the min. required bandwidth - Modulation: - Uses pseudo-noise (PN) sequence to convert the signal into wideband - The PN is random, but can be re-produced by receiver - Demodulation: - Correct correlation using a PN re-produces the signal - Using wrong PN sequence produces noise, hence this scheme is ‘secure’ 6: Wireless and Mobile Networks 6 -54

- Spread Spectrum (SS) uses two techniques: - (1) FHMA: frequency hopped MA - (1) DSMA: direct sequence MA (also called CDMA: code division multiple access) - Frequency Hopped MA (FHMA) - Frequencies of individual users are varied in a pseudo-random fashion within the wideband range - The signal is broken into bursts and each burst is sent on a different frequency 6: Wireless and Mobile Networks 6 -55

CDMA 6: Wireless and Mobile Networks 6 -56

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 6 -57

- Speading the signal power over a wide spread of the frequency spectrum reduces fading effects - only part of the spectrum, hence only part of the signal, is affected by fading - No frequency planning required since users use the same frequency - Soft hand-off can be provided since all the cells use the same frequency. MSC monitors signals. - In soft hand-off the channel (or frequency) remains the same and the base station changes 6: Wireless and Mobile Networks 6 -58

Space Division MA (SDMA) r Controls the radiated energy for each user in space using spot beam (directional) antennas 6: Wireless and Mobile Networks 6 -59

Hybrid Multiple Access Systems - Time division frequency hopping (TDFH): (used in some versions of GSM) - User can hop to new frequency at the start of a new TDMA frame - Hence reducing interference and fading effects - User hops over pre-defined frequencies 6: Wireless and Mobile Networks 6 -60

- FDMA/CDMA: - The available bandwidth is split into subspectra. In each subspectrum CDMA is used - Allows to assign subspectra on-demand 6: Wireless and Mobile Networks 6 -61

FDMA/CDMA 6: Wireless and Mobile Networks 6 -62

Cellular networks: the first hop 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 6: Wireless and Mobile Networks 6 -63

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 CDMA-2000 GPRS EDGE UMT S IS-136 GSM IS-95 Don’t drown in a bowl of alphabet soup: use this for reference only 6: Wireless and Mobile Networks 6 -64

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 data 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 6 -65

Cellular standards: brief survey 3 G systems: voice/data r Universal Mobile Telecommunications Service (UMTS) m data service: High Speed Uplink/Downlink packet Access (HSDPA/HSUPA): 3 Mbps r CDMA-2000: CDMA in TDMA slots m data service: 1 x. Evlution Data Optimized (1 x. EVDO) up to 14 Mbps 6: Wireless and Mobile Networks 6 -66

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 6 -67

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 6 -68

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 6 -69

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 foreign agent: entity in visited network that performs mobility functions on behalf of mobile. 6: Wireless and Mobile Networks 6 -70

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 6 -71

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 6 -72

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 6 -73

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 6 -74

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 6 -75

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 6 -76

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 6 -77

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 6 -78

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 6 -79

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 6 -80

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 6 -81

Mobile IP r RFC 2002, RFC 3344. r Goals: r Attempts to provide support for host mobility while maintaining ‘transparency’: m the correspondent node need not know the location of the mobile node m the connection already established should be maintained during movement even if the mobile node changes its network point of attachment 6: Wireless and Mobile Networks 6 -82

Mobile IP 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 6 -83

Mobile IP r Each mobile node has a home network, home address and home agent Correspondent Node Home Agent (HA) Home Network Mobile Node 6: Wireless and Mobile Networks 6 -84

• When mobile node (MN) moves to a foreign network it obtains a care-of-address (COA) from the foreign agent (FA) that registers it with the home agent (HA) • COA is used by HA to forward packets destined to MN Foreign Agent (FA) Advertisement (FA, COA) Solicitation Foreign Network Correspondent Node Register (HA) Mobile Node Home Agent Home Network 6: Wireless and Mobile Networks 6 -85

Mobile IP: registration example 6: Wireless and Mobile Networks 6 -86

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 6 -87

Packets sent by MN go directly to CN Mobile Node (MN) Correspondent Node (CN) Packets to MN are picked up by the HA and tunneled to MN Home Agent (HA) • Triangle Routing in Mobile-IP 6: Wireless and Mobile Networks 6 -88

Triangular routing can be very inefficient, especially when C << B+A, where A (as shown) is the shortest path from CN to MN C Mobile Node (MN) Correspondent Node (CN) A B Home Agent (HA) • Triangle Routing in Mobile-IP 6: Wireless and Mobile Networks 6 -89

Drawbacks of Mobile IP r Other than (the main problem) of triangular routing m Mobile IP incurs lots of communication with the home agent with every movement m so, may not be fit for ‘micro’ mobility [e. g. , move between rooms or buildings within the same network domain] m handoff delays are significant since registration/packets need to go through the home agent first 6: Wireless and Mobile Networks 6 -90

Suggested solutions r To avoid triangular routing m use ‘route optimization’ m use micro-mobility architectures • Cellular IP (CIP) • Hawaii • Multicast-based Mobility (M&M) 6: Wireless and Mobile Networks 6 -91

(4) CN changes the destination address of the packets to go to MN’s new address (3) When MN gets packets from CN it sends a Binding Update to CN with its new address Mobile Node (MN) Correspondent Node (CN) (2) Initial packets to MN are sent through HA to MN (1) MN registers with HA as in basic Mobile IP. Home Agent (HA) • Route Optimization (simple illustration) 6: Wireless and Mobile Networks 6 -92

r With route optimization m Triangular routing is avoided m Still have problems with micro mobility and smooth hand-off m Need additional mechanisms to deal with these issues, which makes the protocol complex. 6: Wireless and Mobile Networks 6 -93

Micro-Mobility r Hierarchical approach to mobility: m During frequent, intra-domain, movement only local efficient handoff is performed without notifying the home agent (HA) or the correspondent node (CN) m For inter-domain mobility use Mobile IP. Notify HA or CN only during inter-domain movement 6: Wireless and Mobile Networks 6 -94

Distribution tree dynamics while roaming Domain Root FA or CN Wireless link Mobile Node 6: Wireless and Mobile Networks 6 -95

M&M: Join/Prune dynamics to modify distribution Domain Root Wireless link Mobile Node 6: Wireless and Mobile Networks 6 -96

Components of cellular network architecture recall: correspondent wired public telephone network MSC MSC MSC different cellular networks, operated by different providers 6: Wireless and Mobile Networks 6 -97

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 6 -98

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 6 -99

GSM: handoff with common MSC r Handoff goal: route call via new base station (without interruption) r reasons for handoff: VLR Mobile Switching Center old routing old BSS m new routing m new BSS m stronger signal to/from new BSS (continuing connectivity, less battery drain) load balance: free up channel in current BSS GSM doesn’t mandate why to perform handoff (policy), only how (mechanism) r handoff initiated by old BSS 6: Wireless and Mobile Networks 6 -100

GSM: handoff with common MSC VLR Mobile Switching Center 2 4 1 8 old BSS 5 7 3 6 new BSS 1. old BSS informs MSC of impending handoff, provides list of 1+ new BSSs 2. MSC sets up path (allocates resources) to new BSS 3. new BSS allocates radio channel for use by mobile 4. new BSS signals MSC, old BSS: ready 5. old BSS tells mobile: perform handoff to new BSS 6. mobile, new BSS signal to activate new channel 7. mobile signals via new BSS to MSC: handoff complete. MSC reroutes call 8 MSC-old-BSS resources released 6: Wireless and Mobile Networks 6 -101

GSM: handoff between MSCs r anchor MSC: first MSC visited during call home network correspondent Home MSC anchor MSC m call remains routed through anchor MSC r new MSCs add on to end PSTN MSC (a) before handoff of MSC chain as mobile moves to new MSC r IS-41 allows optional path minimization step to shorten multi-MSC chain 6: Wireless and Mobile Networks 6 -102

GSM: handoff between MSCs r anchor MSC: first MSC visited during call home network correspondent Home MSC anchor MSC m call remains routed through anchor MSC r new MSCs add on to end PSTN MSC (b) after handoff of MSC chain as mobile moves to new MSC r IS-41 allows optional path minimization step to shorten multi-MSC chain 6: Wireless and Mobile Networks 6 -103

Mobility: GSM versus Mobile IP GSM element Comment on GSM element Mobile IP element Home system Network to which mobile user’s permanent phone number belongs Home network Gateway Mobile Switching Center, or “home MSC”. Home Location Register (HLR) Home MSC: point of contact to obtain routable address of mobile user. HLR: database in home system containing permanent phone number, profile information, current location of mobile user, subscription information Home agent Visited System Network other than home system where mobile user is currently residing Visited network Visited Mobile services Switching Center. Visitor Location Record (VLR) Visited MSC: responsible for setting up calls Foreign agent to/from mobile nodes in cells associated with MSC. VLR: temporary database entry in visited system, containing subscription information for each visiting mobile user Mobile Station Roaming Number (MSRN), or “roaming number” Routable address for telephone call segment between home MSC and visited MSC, visible to neither the mobile nor the correspondent. Care-ofaddress 6: Wireless and Mobile Networks 6 -104

Wireless, mobility: impact on higher layer protocols r logically, impact should be minimal … m best effort service model remains unchanged m TCP and UDP can (and do) run over wireless, mobile r … but performance-wise: m packet loss/delay due to bit-errors (discarded packets, delays for link-layer retransmissions), and handoff m TCP interprets loss as congestion, will decrease congestion window un-necessarily m delay impairments for real-time traffic m limited bandwidth of wireless links 6: Wireless and Mobile Networks 6 -105

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 6 -106

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 6 -107

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 6 -108

CDMA: two-sender interference 6: Wireless and Mobile Networks 6 -109

Direct Sequence Spread Spectrum r Original signal is m(t) r The spreading signal is p(t) [the PN sequence] r The spread spectrum signal is Sss(t) A single pulse or symbol of the PN waveform is called a chip 6: Wireless and Mobile Networks 6 -110

Sss(t) ~ m(t)p(t)cos(2 fct+ ) B: is the bandwidth of m(t)cos(2 fct+ ) Wss: is the bandwidth of Sss(t) Wss >> B Phase modulation Data m(t) Sss(t) Transmitted Signal p(t) PN Code Generator Oscillator fc Chip Clock Block diagram of a DS-SS system with binary phase modulation Transmitter 6: Wireless and Mobile Networks 6 -111

(A) Symbol Channel (B) encoder f(B, C) (C) Chip Symbol duration for m(t): Ts Chip duration for p(t): Tc Processing Gain PG=Wss/B=Ts/Tc, a measure of interference rejection capability 6: Wireless and Mobile Networks 6 -112

Bit stream (A) Ts Encoded stream (B) m(t) Tc Pseudo-noise sequence (C) p(t) 6: Wireless and Mobile Networks 6 -113

r Example: m f(B, C)=B C, where • 1 1= 0 • 1 0=1 • 0 0=0 m if we have received f(B, C) and we are able to re -generate the PN (C), then we can get B. 6: Wireless and Mobile Networks 6 -114