Slide #1.

Wireless and Mobile Networks Background:  # wireless (mobile) phone subscribers now exceeds # wired phone subscribers!  computer nets: laptops, palmtops, PDAs, Internet-enabled phone promise anytime untethered Internet access  two important (but different) challenges   wireless: communication over wireless link mobility: handling the mobile user who changes point of attachment to network 6: Wireless and Mobile Networks 6-1
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Slide #2.

Outline Introduction Wireless  Wireless links, characteristics  CDMA  IEEE 802.11 wireless LANs (“wi-fi”)  Cellular Internet Access   architecture standards (e.g., GSM) Mobility  Principles: addressing and routing to mobile users  Mobile IP  Handling mobility in cellular networks  Mobility and higherlayer protocols Summary 6: Wireless and Mobile Networks 6-2
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Slide #3.

Elements of a wireless network wireless hosts  laptop, PDA, IP phone  run applications  may be stationary (non-mobile) or mobile network infrastructure  wireless does not always mean mobility 6: Wireless and Mobile Networks 6-3
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Slide #4.

Elements of a wireless network network infrastructure base station  typically connected to wired network  relay - responsible for sending packets between wired network and wireless host(s) in its “area”  e.g., cell towers, 802.11 access points 6: Wireless and Mobile Networks 6-4
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Slide #5.

Elements of a wireless network network infrastructure wireless link  typically used to connect mobile(s) to base station  also used as backbone link  multiple access protocol coordinates link access  various data rates, transmission distance 6: Wireless and Mobile Networks 6-5
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Slide #6.

Characteristics of selected wireless link standards Data rate (Mbps) 200 54 5-11 802.11n 802.11a,g 802.11b 4 1 802.11a,g point-to-point data 802.16 (WiMAX) UMTS/WCDMA-HSPDA, CDMA2000-1xEVDO 3G cellular enhanced 802.15 .384 3G UMTS/WCDMA, CDMA2000 .056 2G IS-95, CDMA, GSM Indoor Outdoor 10-30m 50-200m Mid-range outdoor Long-range outdoor 200m – 4 Km 5Km – 20 Km 6: Wireless and Mobile Networks 6-6
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Slide #7.

Elements of a wireless network network infrastructure infrastructure mode  base station connects mobiles into wired network  handoff: mobile changes base station providing connection into wired network 6: Wireless and Mobile Networks 6-7
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Slide #8.

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 6: Wireless and Mobile Networks 6-8
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Slide #9.

Wireless network taxonomy single hop infrastructure (e.g., APs) no infrastructure host connects to base station (WiFi, WiMAX, cellular) which connects to larger Internet no base station, no connection to larger Internet (Bluetooth, ad hoc nets) 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 6: Wireless and Mobile Networks 6-9
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Slide #10.

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” 6: Wireless and Mobile Networks 6-10
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Slide #11.

Wireless Link Characteristics (2)  SNR: signal-to-noise ratio larger SNR – easier to extract signal from noise (a “good thing”)  SNR versus BER tradeoffs  given physical layer: increase power -> increase SNR->decrease BER  given SNR: choose physical layer that meets BER requirement, giving highest thruput 10-1  • SNR may change with mobility: dynamically adapt physical layer (modulation technique, rate) 10-2 BER 10-3 10-4 10-5 10-6 10-7 10 20 30 40 SNR(dB) QAM256 (8 Mbps) QAM16 (4 Mbps) BPSK (1 Mbps) 6: Wireless and Mobile Networks 6-11
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Slide #12.

Wireless network characteristics Multiple wireless senders and receivers create additional problems (beyond multiple access): B A C C A B Hidden terminal problem  B, A hear each other  B, C hear each other  A, C can not hear each other means A, C unaware of their interference at B C’s signal strength A’s signal strength space Signal attenuation:  B, A hear each other  B, C hear each other  A, C can not hear each other interfering at B 6: Wireless and Mobile Networks 6-12
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Slide #13.

Code Division Multiple Access (CDMA)  used in several wireless broadcast channels      (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 6-13
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Slide #14.

CDMA Encode/Decode sender data bits code Zi,m= di.cm d0 = 1 -1 -1 -1 1 -1 1 1 1 -1 -1 -1 slot 1 -1 slot 1 channel output 1 -1 1 1 1 1 1 1 1 d1 = -1 1 1 1 channel output Zi,m -1 -1 -1 slot 0 1 -1 -1 -1 -1 slot 0 channel output M Di =  Zi,m.cm m=1 received input code receiver 1 1 1 1 1 1 1 -1 -1 -1 -1 1 1 1 1 -1 -1 -1 -1 -1 1 1 1 -1 -1 -1 slot 1 M 1 1 -1 -1 -1 -1 slot 0 d0 = 1 d1 = -1 slot 1 channel output slot 0 channel output 6: Wireless and Mobile Networks 6-14
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Slide #15.

CDMA: two-sender interference 6: Wireless and Mobile Networks 6-15
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Slide #16.

Outline 1 Introduction Wireless  2 Wireless links, characteristics  CDMA  3 IEEE 802.11 wireless LANs (“wi-fi”)  4 cellular Internet access   architecture standards (e.g., GSM) Mobility  5 Principles: addressing and routing to mobile users  6 Mobile IP  7 Handling mobility in cellular networks  8 Mobility and higherlayer protocols 9 Summary 6: Wireless and Mobile Networks 6-16
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Slide #17.

IEEE 802.11 Wireless LAN  802.11b  2.4-5 GHz unlicensed spectrum  up to 11 Mbps  direct sequence spread spectrum (DSSS) in physical layer • all hosts use same chipping code  802.11a  5-6 GHz range  up to 54 Mbps  802.11g   2.4-5 GHz range up to 54 Mbps  802.11n: multiple antennae  2.4-5 GHz range  up to 200 Mbps  all use CSMA/CA for multiple access  all have base-station and ad-hoc network versions 6: Wireless and Mobile Networks 6-17
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Slide #18.

802.11 LAN architecture  wireless host Internet AP BSS 1 hub, switch or router AP BSS 2 communicates with base station  base station = access point (AP)  Basic Service Set (BSS) (aka “cell”) in infrastructure mode contains:  wireless hosts  access point (AP): base station  ad hoc mode: hosts only 6: Wireless and Mobile Networks 6-18
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Slide #19.

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  will typically run DHCP to get IP address in AP’s subnet 6: Wireless and Mobile Networks 6-19
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Slide #20.

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 2 3 AP 2 4 H1 H1 Passive Scanning: Active Scanning: (1) beacon frames sent from APs (2) association Request frame sent: H1 to selected AP (3) association Response frame sent: H1 to selected AP (1) Probe Request frame broadcast from H1 (2) Probes response frame sent from APs (3) Association Request frame sent: H1 to selected AP (4) Association Response frame sent: H1 to selected AP 6: Wireless and Mobile Networks 6-20
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Slide #21.

IEEE 802.11: multiple access  avoid collisions: 2+ nodes transmitting at same time  802.11: CSMA - sense before transmitting  don’t collide with ongoing transmission by other node  802.11: no collision detection!  difficult to receive (sense collisions) when transmitting due to weak received signals (fading)  can’t sense all collisions in any case: hidden terminal, fading  goal: avoid collisions: CSMA/C(ollision)A(voidance) B A C C A B C’s signal strength A’s signal strength space 6: Wireless and Mobile Networks 6-21
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Slide #22.

IEEE 802.11 MAC Protocol: CSMA/CA DIFS: distributed inter-frame space 802.11 senderSIFS: shortest inter-frame space 1 if sense channel idle for DIFS then sender transmit entire frame (no CD) 2 if sense channel busy then start random backoff time timer counts down while channel idle transmit when timer expires if no ACK, increase random backoff interval, repeat 2 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 6-22
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Slide #23.

Avoiding collisions (more) idea: allow sender to “reserve” channel rather than random access of data frames: avoid collisions of long data frames  sender first transmits small request-to-send (RTS) packets to BS using CSMA  RTSs may still collide with each other (but they’re short)  BS broadcasts clear-to-send CTS in response to RTS  CTS heard by all nodes  sender transmits data frame  other stations defer transmissions avoid data frame collisions completely using small reservation packets! 6: Wireless and Mobile Networks 6-23
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Slide #24.

Collision Avoidance: RTS-CTS exchange A B AP RTS(B) RTS(A) reservation collision RTS(A) CTS(A) CTS(A) DATA (A) time ACK(A) defer ACK(A) 6: Wireless and Mobile Networks 6-24
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Slide #25.

802.11 frame: addressing 2 2 6 6 6 frame address address address duration control 1 2 3 Address 1: MAC address of wireless host or AP to receive this frame 2 6 0 - 2312 4 payload CRC seq address 4 control 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 6-25
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Slide #26.

802.11 frame: addressing R1 router H1 Internet AP R1 MAC addr H1 MAC addr dest. address source address 802.3 frame AP MAC addr H1 MAC addr R1 MAC addr address 1 address 2 address 3 802.11 frame 6: Wireless and Mobile Networks 6-26
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Slide #27.

802.11 frame: more duration of reserved transmission time (RTS/CTS) 2 2 6 6 6 Protocol version 2 4 1 Type Subtype To AP 6 2 frame address address address duration control 1 2 3 2 frame seq # (for RDT) 1 seq address 4 control 1 1 From More AP frag 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 6-27
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Slide #28.

802.11: mobility within same subnet  H1 remains in same IP subnet: IP address can remain same  switch: which AP is associated with H1?  self-learning (Ch. 5): switch will see frame from H1 and “remember” which switch port can be used to reach H1 router hub or switch BBS 1 AP 1 AP 2 H1 BBS 2 6: Wireless and Mobile Networks 6-28
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Slide #29.

802.11: advanced capabilities QAM256 (8 Mbps) QAM16 (4 Mbps) BPSK (1 Mbps) operating point 10-1 10-2 10-3 BER Rate Adaptation  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(dB) 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 6-29
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Slide #30.

802.11: advanced capabilities Power Management  node-to-AP: “I am going to sleep until next beacon frame”  AP knows not to transmit frames to this node  node wakes up before next beacon frame  beacon frame: contains list of mobiles with AP-to-mobile frames waiting to be sent  node will stay awake if AP-to-mobile frames to be sent; otherwise sleep again until next beacon frame 6: Wireless and Mobile Networks 6-30
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Slide #31.

802.15: personal area network  less than 10 m diameter  replacement for cables (mouse, keyboard, headphones)  ad hoc: no infrastructure  master/slaves:   slaves request permission to send (to master) master grants requests  802.15: evolved from Bluetooth specification   2.4-2.5 GHz radio band up to 721 kbps P S P radius of coverage M S P S P M Master device S Slave device P Parked device (inactive) 6: Wireless and Mobile Networks 6-31
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Slide #32.

802.16: WiMAX  like 802.11 & cellular: point-to-point base station model transmissions to/from base station by hosts with omnidirectional antenna  base station-to-base station backhaul with point-to-point antenna  point-to-multipoint  unlike 802.11:  range ~ 6 miles (“city rather than coffee shop”)  ~14 Mbps 6: Wireless and Mobile Networks 6-32
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Slide #33.

802.16: WiMAX: downlink, uplink scheduling  transmission frame  down-link subframe: base station to node  uplink subframe: node to base station pream. … DL- ULMAP MAP 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  WiMAX standard provide mechanism for scheduling, but not scheduling algorithm 6: Wireless and Mobile Networks 6-33
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Slide #34.

Chapter 6 outline 6.1 Introduction Wireless  6.2 Wireless links, characteristics  CDMA  6.3 IEEE 802.11 wireless LANs (“wi-fi”)  6.4 Cellular Internet Access   architecture standards (e.g., GSM) Mobility  6.5 Principles: addressing and routing to mobile users  6.6 Mobile IP  6.7 Handling mobility in cellular networks  6.8 Mobility and higher-layer protocols 6.9 Summary 6: Wireless and Mobile Networks 6-34
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Slide #35.

Components of cellular network architecture MSC cell  connects cells to wide area net  manages call setup (more later!)  handles mobility (more later!)  covers geographical region  base station (BS) analogous to 802.11 AP  mobile users attach to network through BS  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 6-35
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Slide #36.

Cellular networks: the first hop Two techniques for sharing mobile-to-BS radio spectrum  combined FDMA/TDMA: divide spectrum in frequency channels, divide each channel into time slots frequency  CDMA: code division bands multiple access time slots 6: Wireless and Mobile Networks 6-36
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Slide #37.

Cellular standards: brief survey 2G systems: voice channels  IS-136 TDMA: combined FDMA/TDMA (north america)  GSM (global system for mobile communications): combined FDMA/TDMA  most widely deployed  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 6-37
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Slide #38.

Cellular standards: brief survey 2.5 G systems: voice and data channels  for those who can’t wait for 3G service: 2G extensions  general packet radio service (GPRS)   evolved from GSM data sent on multiple channels (if available)  enhanced data rates for global evolution (EDGE)  also evolved from GSM, using enhanced modulation  data rates up to 384K  CDMA-2000 (phase 1)   data rates up to 144K evolved from IS-95 6: Wireless and Mobile Networks 6-38
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Slide #39.

Cellular standards: brief survey 3G systems: voice/data  Universal Mobile Telecommunications Service (UMTS)  data service: High Speed Uplink/Downlink packet Access (HSDPA/HSUPA): 3 Mbps  CDMA-2000: CDMA in TDMA slots  data service: 1xEvlution Data Optimized (1xEVDO) up to 14 Mbps ….. more (and more interesting) cellular topics due to mobility (stay tuned for details) 6: Wireless and Mobile Networks 6-39
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Slide #40.

Chapter 6 outline 6.1 Introduction Wireless  6.2 Wireless links, characteristics  CDMA  6.3 IEEE 802.11 wireless LANs (“wi-fi”)  6.4 Cellular Internet Access   architecture standards (e.g., GSM) Mobility  6.5 Principles: addressing and routing to mobile users  6.6 Mobile IP  6.7 Handling mobility in cellular networks  6.8 Mobility and higher-layer protocols 6.9 Summary 6: Wireless and Mobile Networks 6-40
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Slide #41.

What is mobility?  spectrum of mobility, from the network perspective: no mobility mobile wireless user, mobile user, using same access connecting/ point disconnecting from network using DHCP. high mobility mobile user, passing through multiple access point while maintaining ongoing connections (like cell phone) 6: Wireless and Mobile Networks 6-41
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Slide #42.

Mobility: Vocabulary home network: permanent “home” of mobile (e.g., 128.119.40/24) home agent: entity that will perform mobility functions on behalf of mobile, when mobile is remote wide area network Permanent address: address in home network, can always be used to reach mobile correspondent e.g., 128.119.40.186 6: Wireless and Mobile Networks 6-42
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Slide #43.

Mobility: more vocabulary visited network: network in which mobile currently resides (e.g., Permanent address: remains constant (e.g., 79.129.13/24) 128.119.40.186) 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 ofMobile mobile. 6: Wireless and Networks 6-43
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Slide #44.

How do you contact a mobile friend: Consider friend frequently changing addresses, how do you find her? I wonder where Alice moved to?  search all phone books?  call her parents?  expect her to let you know where he/she is? 6: Wireless and Mobile Networks 6-44
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Slide #45.

Mobility: approaches  Let routing handle it: routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange.  routing tables indicate where each mobile located  no changes to end-systems  Let end-systems handle it:  indirect routing: communication from correspondent to mobile goes through home agent, then forwarded to remote  direct routing: correspondent gets foreign address of mobile, sends directly to mobile 6: Wireless and Mobile Networks 6-45
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Slide #46.

Mobility: approaches  Let routing handle it: routers advertise permanent address of mobile-nodes-in-residence via usual not scalable routing table exchange. millions of  routing tables to indicate where each mobile located mobiles  no changes to end-systems  let end-systems handle it:  indirect routing: communication from correspondent to mobile goes through home agent, then forwarded to remote  direct routing: correspondent gets foreign address of mobile, sends directly to mobile 6: Wireless and Mobile Networks 6-46
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Slide #47.

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:  Foreign agent knows about mobile  Home agent knows location of mobile 6: Wireless and Mobile Networks 6-47
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Slide #48.

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 1 correspondent addresses packets using home address of mobile 2 4 mobile replies directly to correspondent 6: Wireless and Mobile Networks 6-48
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Slide #49.

Indirect Routing: comments  Mobile uses two addresses:  permanent address: used by correspondent (hence mobile location is transparent to correspondent)  care-of-address: used by home agent to forward datagrams to mobile  foreign agent functions may be done by mobile itself  triangle routing: correspondent-home-network-mobile  inefficient when correspondent, mobile are in same network 6: Wireless and Mobile Networks 6-49
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Slide #50.

Indirect Routing: moving between networks  suppose mobile user moves to another network  registers with new foreign agent  new foreign agent registers with home agent  home agent update care-of-address for mobile  packets continue to be forwarded to mobile (but with new care-of-address)  mobility, changing foreign networks transparent: on going connections can be maintained! 6: Wireless and Mobile Networks 6-50
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Slide #51.

Mobility via Direct Routing foreign agent receives packets, forwards to mobile correspondent forwards to foreign agent 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 6-51
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Slide #52.

Mobility via Direct Routing: comments  overcome triangle routing problem  non-transparent to correspondent: correspondent must get care-of-address from home agent  what if mobile changes visited network? 6: Wireless and Mobile Networks 6-52
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Slide #53.

Accommodating mobility with direct routing  anchor foreign agent: FA in first visited network  data always routed first to anchor FA  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 correspondent agent 3 new foreign agent new foreign network 6: Wireless and Mobile Networks 6-53
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Slide #54.

Chapter 6 outline 6.1 Introduction Wireless  6.2 Wireless links, characteristics  CDMA  6.3 IEEE 802.11 wireless LANs (“wi-fi”)  6.4 Cellular Internet Access   architecture standards (e.g., GSM) Mobility  6.5 Principles: addressing and routing to mobile users  6.6 Mobile IP  6.7 Handling mobility in cellular networks  6.8 Mobility and higher-layer protocols 6.9 Summary 6: Wireless and Mobile Networks 6-54
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Slide #55.

Mobile IP  RFC 3344  has many features we’ve seen:  home agents, foreign agents, foreign-agent registration, care-of-addresses, encapsulation (packet-within-a-packet)  three components to standard:  indirect routing of datagrams  agent discovery  registration with home agent 6: Wireless and Mobile Networks 6-55
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Slide #56.

Mobile IP: indirect routing packet sent by home agent to foreign agent: a packet within a packet dest: 79.129.13.2 foreign-agent-to-mobile packet dest: 128.119.40.186 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 6-56
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Slide #57.

Mobile IP: agent discovery  agent advertisement: foreign/home agents advertise service by broadcasting ICMP messages (typefield = 9) 16 0 8 24 type = 9 H,F bits: home and/or foreign agent R bit: registration required checksum =9 code = 0 =9 standard ICMP fields router address type = 16 length registration lifetime sequence # RBHFMGV bits reserved 0 or more care-ofaddresses mobility agent advertisement extension 6: Wireless and Mobile Networks 6-57
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Slide #58.

Mobile IP: registration example visited network: 79.129.13/ 24 home agent HA: 128.119.40.7 f oreign agent COA: 79.129.13.2 I CMP agent adv. COA: 79.129.13.2 …. registration req. COA: 79.129.13.2 HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 9999 identification: 714 encapsulation format …. Mobile agent MA: 128.119.40.186 registration req. COA: 79.129.13.2 HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 9999 identification:714 …. registration reply time HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 4999 Identification: 714 encapsulation format …. registration reply HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 4999 Identification: 714 …. 6: Wireless and Mobile Networks 6-58
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Slide #59.

Components of cellular network architecture recall: correspondent wired public telephone network MSC MSC MSC MSC MSC different cellular networks, operated by different providers 6: Wireless and Mobile Networks 6-59
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Slide #60.

Handling mobility in cellular networks  home network: network of cellular provider you subscribe to (e.g., Sprint PCS, Verizon)  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)  visited network: network in which mobile currently resides  visitor location register (VLR): database with entry for each user currently in network  could be home network 6: Wireless and Mobile Networks 6-60
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Slide #61.

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 2nd 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 6-61
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Slide #62.

GSM: handoff with common MSC  Handoff goal: route call via new base station (without interruption)  reasons for handoff: VLR Mobile Switching Center old routing old BSS  new routing  new BSS  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)  handoff initiated by old BSS 6: Wireless and Mobile Networks 6-62
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Slide #63.

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 6-63
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Slide #64.

GSM: handoff between MSCs  anchor MSC: first MSC visited during cal home network correspondent Home MSC anchor MSC MSC  call remains routed through anchor MSC  new MSCs add on to PSTN MSC MSC (a) before handoff end of MSC chain as mobile moves to new MSC  IS-41 allows optional path minimization step to shorten multi-MSC chain 6: Wireless and Mobile Networks 6-64
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Slide #65.

GSM: handoff between MSCs  anchor MSC: first MSC visited during cal home network correspondent Home MSC anchor MSC MSC  call remains routed through anchor MSC  new MSCs add on to PSTN MSC MSC (b) after handoff end of MSC chain as mobile moves to new MSC  IS-41 allows optional path minimization step to shorten multi-MSC chain 6: Wireless and Mobile Networks 6-65
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Slide #66.

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 6-66
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Slide #67.

Wireless, mobility: impact on higher layer protocols  logically, impact should be minimal … best effort service model remains unchanged  TCP and UDP can (and do) run over wireless, mobile  … but performance-wise:  packet loss/delay due to bit-errors (discarded packets, delays for link-layer retransmissions), and handoff  TCP interprets loss as congestion, will decrease congestion window un-necessarily  delay impairments for real-time traffic  limited bandwidth of wireless links  6: Wireless and Mobile Networks 6-67
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Slide #68.

Chapter 6 Summary Wireless  wireless links:    capacity, distance channel impairments CDMA  IEEE 802.11 (“wi-fi”)  CSMA/CA reflects wireless channel characteristics  cellular access   architecture standards (e.g., GSM, CDMA-2000, UMTS) Mobility  principles: addressing, routing to mobile users    home, visited networks direct, indirect routing care-of-addresses  case studies  mobile IP  mobility in GSM  impact on higher-layer protocols 6: Wireless and Mobile Networks 6-68
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