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6: Wireless and Mobile Networks6-1 Chapter 6 Wireless and Mobile Networks Computer Networking: A Top Down Approach 4 th edition. Jim Kurose, Keith Ross.

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Presentation on theme: "6: Wireless and Mobile Networks6-1 Chapter 6 Wireless and Mobile Networks Computer Networking: A Top Down Approach 4 th edition. Jim Kurose, Keith Ross."— Presentation transcript:

1 6: Wireless and Mobile Networks6-1 Chapter 6 Wireless and Mobile Networks Computer Networking: A Top Down Approach 4 th edition. Jim Kurose, Keith Ross Addison-Wesley, July Computer Networking: A Top Down Approach 5 th edition. Jim Kurose, Keith Ross Addison-Wesley, April 2009.

2 6: Wireless and Mobile Networks6-2 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 wireless: communication over wireless link m mobility: handling the mobile user who changes point of attachment to network

3 6: Wireless and Mobile Networks6-3 Chapter 6 outline 6.1 Introduction Wireless r 6.2 Wireless links, characteristics r 6.3 IEEE wireless LANs (wi-fi) r 6.4 Cellular Internet Access m architecture m 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 higher- layer protocols 6.9 Summary

4 6: Wireless and Mobile Networks6-4 Elements of a wireless network network infrastructure wireless hosts r laptop, PDA, IP phone r run applications r may be stationary (non-mobile) or mobile m wireless does not always mean mobility

5 6: Wireless and Mobile Networks6-5 Elements of a wireless network 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, access points

6 6: Wireless and Mobile Networks6-6 Elements of a wireless network 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

7 6: Wireless and Mobile Networks6-7 Characteristics of selected wireless link standards Indoor 10-30m Outdoor m Mid-range outdoor 200m – 4 Km Long-range outdoor 5Km – 20 Km IS-95, CDMA, GSM 2G UMTS/WCDMA, CDMA2000 3G b a,g UMTS/WCDMA-HSPDA, CDMA2000-1xEVDO 3G cellular enhanced (WiMAX) a,g point-to-point n Data rate (Mbps) data

8 6: Wireless and Mobile Networks6-8 Elements of a wireless network network infrastructure infrastructure mode r base station connects mobiles into wired network r handoff: mobile changes base station providing connection into wired network

9 6: Wireless and Mobile Networks6-9 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

10 6: Wireless and Mobile Networks6-10 Wireless network taxonomy single hop multiple hops 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) 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 Mobile Adhoc Networks Vehicular Adhoc Networks

11 6: Wireless and Mobile Networks6-11 Wireless Communication Systems & Networking - What complicates wireless networking vs. wired networking?

12 6: Wireless and Mobile Networks 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 Mobility: continuous and introduces topology dynamics - 3- Power constraints in lots of the wireless devices

13 6: Wireless and Mobile Networks6-13 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

14 6: Wireless and Mobile Networks6-14 Wireless Link Characteristics (2) r SNR: signal-to-noise ratio m 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 SNR may change with mobility: dynamically adapt physical layer (modulation technique, rate) QAM256 (8 Mbps) QAM16 (4 Mbps) BPSK (1 Mbps) SNR(dB) BER Quadrature Amplitude Modulation (QAM) Binary Phase Shift Keying (BPSK)

15 6: Wireless and Mobile Networks6-15 Wireless network characteristics Multiple wireless senders and receivers create additional problems (beyond multiple access): A B C Hidden terminal problem r B, A hear each other r B, C hear each other r A, C can not hear each other means A, C unaware of their interference at B A B C As signal strength space Cs signal strength Signal attenuation: r B, A hear each other r B, C hear each other r A, C can not hear each other interfering at B

16 6: Wireless and Mobile Networks6-16 Chapter 6 outline 6.1 Introduction Wireless r 6.2 Wireless links, characteristics m CDMA r 6.3 IEEE wireless LANs (wi-fi) r 6.4 cellular Internet access m architecture m 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 higher- layer protocols 6.9 Summary

17 6: Wireless and Mobile Networks6-17 IEEE Wireless LAN r b m GHz unlicensed spectrum m up to 11 Mbps m direct sequence spread spectrum (DSSS) in physical layer (CDMA: code division multiple access) all hosts use same chipping code r a m 5-6 GHz range m up to 54 Mbps r g m GHz range m up to 54 Mbps r n: multiple antennae m GHz range m up to 200 Mbps r all use CSMA/CA for multiple access r all have base-station and ad-hoc network versions

18 6: Wireless and Mobile Networks LAN architecture r wireless host communicates 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 BSS 1 BSS 2 Internet hub, switch or router AP

19 6: Wireless and Mobile Networks : Channels, association r b: 2.4GHz-2.485GHz 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 APs 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 APs subnet

20 6: Wireless and Mobile Networks : passive/active scanning AP 2 AP 1 H1 BBS 2 BBS Active Scanning : (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: selected AP to H1 AP 2 AP 1 H1 BBS 2 BBS Passive Scanning: (1)beacon frames sent from APs (2)association Request frame sent: H1 to selected AP (3)association Response frame sent: selected AP to H1

21 6: Wireless and Mobile Networks6-21 IEEE : multiple access r avoid collisions: 2 + nodes transmitting at same time r : CSMA - sense before transmitting m dont collide with ongoing transmission by other node r : no collision detection! m difficult to receive (sense collisions) when transmitting due to weak received signals (fading) m cant sense all collisions in any case: hidden terminal, fading m goal: avoid collisions: CSMA/C(ollision)A(voidance) A B C A B C As signal strength space Cs signal strength

22 6: Wireless and Mobile Networks6-22 IEEE MAC Protocol: CSMA/CA sender 1 if sense channel idle for DIFS then 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 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)

23 6: Wireless and Mobile Networks6-23 Hidden Terminal Problem in WLANs

24 6: Wireless and Mobile Networks6-24 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 theyre 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!

25 6: Wireless and Mobile Networks6-25 Collision Avoidance: RTS-CTS exchange AP A B time RTS(A) RTS(B) RTS(A) CTS(A) DATA (A) ACK(A) reservation collision defer

26 6: Wireless and Mobile Networks6-26 Check Animations on-line (applet & ns)

27 6: Wireless and Mobile Networks6-27 frame control duration address 1 address 2 address 4 address 3 payloadCRC seq control frame: addressing Address 2: MAC address of wireless host or AP transmitting this frame Address 1: MAC address of wireless host or AP to receive this frame Address 3: MAC address of router interface to which AP is attached Address 4: used only in ad hoc mode

28 6: Wireless and Mobile Networks6-28 Internet router AP H1 R1 AP MAC addr H1 MAC addr R1 MAC addr address 1 address 2 address frame R1 MAC addr AP MAC addr dest. address source address frame frame: addressing

29 6: Wireless and Mobile Networks6-29 frame control duration address 1 address 2 address 4 address 3 payloadCRC seq control Type From AP Subtype To AP More frag WEP More data Power mgt RetryRsvd Protocol version frame: more duration of reserved transmission time (RTS/CTS) frame seq # (for reliable ARQ) frame type (RTS, CTS, ACK, data)

30 6: Wireless and Mobile Networks6-30 hub or switch AP 2 AP 1 H1 BBS 2 BBS : mobility within same subnet router r H1 remains in same IP subnet: IP address can remain same r switch: which AP is associated with H1? m self-learning (Ch. 5): switch will see frame from H1 and remember which switch port can be used to reach H1

31 6: Wireless and Mobile Networks : advanced capabilities Rate Adaptation r base station, mobile dynamically change transmission rate (physical layer modulation technique) as mobile moves, SNR varies QAM256 (8 Mbps) QAM16 (4 Mbps) BPSK (1 Mbps) SNR(dB) BER operating point 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 Rate adaptation can change rate from 100Mbps to 1Mbps !! Does this affect higher protocol layers?

32 6: Wireless and Mobile Networks : 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 m node wakes up before next beacon frame r beacon frame: contains list of mobiles with AP- to-mobile frames waiting to be sent m node will stay awake if AP-to-mobile frames to be sent; otherwise sleep again until next beacon frame (typically after 100msec)

33 6: Wireless and Mobile Networks6-33 M radius of coverage S S S P P P P M S Master device Slave device Parked device (inactive) P : 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 slaves request permission to send (to master) m master grants requests r : evolved from Bluetooth specification m GHz radio band m up to 721 kbps

34 6: Wireless and Mobile Networks : WiMAX r like & cellular: 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 r unlike : m range ~ 6 miles (city rather than coffee shop) m ~14 Mbps point-to-multipoint point-to-point

35 6: Wireless and Mobile Networks : WiMAX: downlink, uplink scheduling r transmission frame m down-link subframe: base station to node m uplink subframe: node to base station pream. DL- MAP UL- MAP DL burst 1 SS #1 DL burst 2 DL burst n Initial maint. request conn. downlink subframe SS #2 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 WiMAX standard provide mechanism for scheduling, but not scheduling algorithm

36 6: Wireless and Mobile Networks6-36 Chapter 6 outline 6.1 Introduction Wireless r 6.2 Wireless links, characteristics m CDMA r 6.3 IEEE wireless LANs (wi-fi) r 6.4 Cellular Internet Access m architecture m 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 higher- layer protocols 6.9 Summary

37 6: Wireless and Mobile Networks6-37 Mobile Switching Center Public telephone network, and Internet Mobile Switching Center Components of cellular network architecture connects cells to wide area net manages call setup (more later!) handles mobility (more later!) MSC covers geographical region base station (BS) analogous to AP mobile users attach to network through BS air-interface: physical and link layer protocol between mobile and BS cell wired network

38 6: Wireless and Mobile Networks6-38 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)

39 6: Wireless and Mobile Networks6-39

40 6: Wireless and Mobile Networks6-40

41 6: Wireless and Mobile Networks6-41 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)

42 6: Wireless and Mobile Networks6-42 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 un- interrupted. [the hand-off problem]

43 6: Wireless and Mobile Networks6-43

44 6: Wireless and Mobile Networks6-44 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)

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

46 6: Wireless and Mobile Networks6-46 Frequency Re-use - A cell uses a set of frequencies - A cluster holds several cells - Frequency re-use factor: 1/#cells per cluster

47 6: Wireless and Mobile Networks6-47 F C B D E A G F C B D E A G F C B D E A G F C B D E A G F C B D E A G 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. Cell Cluster This requires channel/frequency planning and allocation!

48 6: Wireless and Mobile Networks6-48 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

49 6: Wireless and Mobile Networks6-49 FDMA

50 6: Wireless and Mobile Networks6-50 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

51 6: Wireless and Mobile Networks6-51 TDMA

52 6: Wireless and Mobile Networks6-52 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

53 6: Wireless and Mobile Networks6-53 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 !!

54 6: Wireless and Mobile Networks6-54 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

55 6: Wireless and Mobile Networks 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

56 6: Wireless and Mobile Networks6-56 CDMA

57 6: Wireless and Mobile Networks6-57 Code Division Multiple Access (CDMA) r used in several wireless broadcast channels (cellular, satellite, etc) standards r unique code assigned to each user; i.e., code set partitioning r all users share same frequency, but each user has own chipping sequence (i.e., code) to encode data r encoded signal = (original data) X (chipping sequence) r decoding: inner-product of encoded signal and chipping sequence r allows multiple users to coexist and transmit simultaneously with minimal interference (if codes are orthogonal)

58 6: Wireless and Mobile Networks 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

59 6: Wireless and Mobile Networks6-59 Space Division MA (SDMA) r Controls the radiated energy for each user in space using spot beam (directional) antennas

60 6: Wireless and Mobile Networks6-60 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

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

62 6: Wireless and Mobile Networks6-62 FDMA/CDMA

63 6: Wireless and Mobile Networks6-63 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 time slots

64 6: Wireless and Mobile Networks6-64 Cellular standards: brief survey 2G 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 IS-136 GSM IS-95 GPRS EDGE CDMA-2000 UMTS TDMA/FDMA Dont drown in a bowl of alphabet soup: use this for reference only

65 6: Wireless and Mobile Networks6-65 Cellular standards: brief survey 2.5 G systems: voice and data channels r for those who cant wait for 3G service: 2G 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 384K r CDMA-2000 (phase 1) m data rates up to 144K m evolved from IS-95

66 6: Wireless and Mobile Networks6-66 Cellular standards: brief survey 3G 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: 1xEvlution Data Optimized (1xEVDO) up to 14 Mbps

67 6: Wireless and Mobile Networks6-67 Chapter 6 outline 6.1 Introduction Wireless r 6.2 Wireless links, characteristics m CDMA r 6.3 IEEE wireless LANs (wi-fi) r 6.4 Cellular Internet Access m architecture m 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 higher- layer protocols 6.9 Summary

68 6: Wireless and Mobile Networks6-68 What is mobility? r spectrum of mobility, from the network perspective: no mobility high mobility mobile wireless user, using same access point mobile user, passing through multiple access point while maintaining ongoing connections ( like cell phone) mobile user, connecting/ disconnecting from network using DHCP.

69 6: Wireless and Mobile Networks6-69 Mobility: Vocabulary home network: permanent home of mobile (e.g., /24) Permanent address: address in home network, can always be used to reach mobile e.g., home agent: entity that will perform mobility functions on behalf of mobile, when mobile is remote wide area network correspondent

70 6: Wireless and Mobile Networks6-70 Mobility: more vocabulary Care-of-address: address in visited network. (e.g., 79, ) wide area network visited network: network in which mobile currently resides (e.g., /24) Permanent address: remains constant ( e.g., ) foreign agent: entity in visited network that performs mobility functions on behalf of mobile. correspondent: wants to communicate with mobile

71 6: Wireless and Mobile Networks6-71 How do you contact a mobile friend: r search all phone books? r call her parents? r expect her to let you know where he/she is? I wonder where Alice moved to? Consider friend frequently changing addresses, how do you find her?

72 6: Wireless and Mobile Networks6-72 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

73 6: Wireless and Mobile Networks6-73 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 not scalable to millions of mobiles

74 6: Wireless and Mobile Networks6-74 Mobility: registration End result: r Foreign agent knows about mobile r Home agent knows location of mobile wide area network home network visited network 1 mobile contacts foreign agent on entering visited network 2 foreign agent contacts home agent home: this mobile is resident in my network

75 6: Wireless and Mobile Networks6-75 Mobility via Indirect Routing wide area network home network visited network correspondent addresses packets using home address of mobile home agent intercepts packets, forwards to foreign agent foreign agent receives packets, forwards to mobile mobile replies directly to correspondent

76 6: Wireless and Mobile Networks6-76 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-network- mobile m inefficient when correspondent, mobile are in same network

77 6: Wireless and Mobile Networks6-77 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!

78 6: Wireless and Mobile Networks6-78 Mobility via Direct Routing wide area network home network visited network correspondent requests, receives foreign address of mobile correspondent forwards to foreign agent foreign agent receives packets, forwards to mobile mobile replies directly to correspondent 3

79 6: Wireless and Mobile Networks6-79 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?

80 6: Wireless and Mobile Networks6-80 wide area network 1 foreign net visited at session start anchor foreign agent 2 4 new foreign agent 3 5 correspondent agent correspondent new foreign network 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)

81 6: Wireless and Mobile Networks6-81 Chapter 6 outline 6.1 Introduction Wireless r 6.2 Wireless links, characteristics m CDMA r 6.3 IEEE wireless LANs (wi-fi) r 6.4 Cellular Internet Access m architecture m 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 higher- layer protocols 6.9 Summary

82 6: Wireless and Mobile Networks6-82 Mobile IP r RFC 2002, RFC 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

83 6: Wireless and Mobile Networks6-83 Mobile IP r has many features weve seen: m home agents, foreign 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

84 6: Wireless and Mobile Networks6-84 Mobile IP r Each mobile node has a home network, home address and home agent Home Agent (HA) Home Network Mobile Node Correspondent Node

85 6: Wireless and Mobile Networks6-85 Home Agent Home Network Correspondent Node Foreign Agent (FA) Foreign Network Mobile Node 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 Solicitation Advertisement (FA,COA) Register (HA) Register

86 6: Wireless and Mobile Networks6-86 Mobile IP: registration example

87 6: Wireless and Mobile Networks6-87 Mobile IP: indirect routing Permanent address: Care-of address: dest: packet sent by correspondent dest: dest: packet sent by home agent to foreign agent: a packet within a packet dest: foreign-agent-to-mobile packet

88 6: Wireless and Mobile Networks6-88 Home Agent (HA) Correspondent Node (CN) Mobile Node (MN) Packets to MN are picked up by the HA and tunneled to MN Packets sent by MN go directly to CN Triangle Routing in Mobile-IP

89 6: Wireless and Mobile Networks6-89 Home Agent (HA) Correspondent Node (CN) Mobile Node (MN) Triangle Routing in Mobile-IP C AB Triangular routing can be very inefficient, especially when C << B+A, where A (as shown) is the shortest path from CN to MN

90 6: Wireless and Mobile Networks6-90 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

91 6: Wireless and Mobile Networks6-91 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)

92 6: Wireless and Mobile Networks6-92 Home Agent (HA) Correspondent Node (CN) Mobile Node (MN) (2) Initial packets to MN are sent through HA to MN (3) When MN gets packets from CN it sends a Binding Update to CN with its new address Route Optimization (simple illustration) (1) MN registers with HA as in basic Mobile IP. (4) CN changes the destination address of the packets to go to MNs new address

93 6: Wireless and Mobile Networks6-93 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.

94 6: Wireless and Mobile Networks6-94 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

95 6: Wireless and Mobile Networks6-95 Distribution tree dynamics while roaming Domain Root Wireless link Mobile Node FA or CN

96 6: Wireless and Mobile Networks6-96 M&M: Join/Prune dynamics to modify distribution Domain Root Wireless link Mobile Node

97 6: Wireless and Mobile Networks6-97 Components of cellular network architecture correspondent MSC wired public telephone network different cellular networks, operated by different providers recall:

98 6: Wireless and Mobile Networks6-98 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

99 6: Wireless and Mobile Networks6-99 Public switched telephone network mobile user home Mobile Switching Center HLR home network visited network correspondent Mobile Switching Center VLR GSM: indirect routing to mobile 1 call routed to home network 2 home MSC consults HLR, gets roaming number of mobile in visited network 3 home MSC sets up 2 nd leg of call to MSC in visited network 4 MSC in visited network completes call through base station to mobile

100 6: Wireless and Mobile Networks6-100 Mobile Switching Center VLR old BSS new BSS old routing new routing GSM: handoff with common MSC r Handoff goal: route call via new base station (without interruption) r reasons for handoff: m stronger signal to/from new BSS (continuing connectivity, less battery drain) m load balance: free up channel in current BSS m GSM doesnt mandate why to perform handoff (policy), only how (mechanism) r handoff initiated by old BSS

101 6: Wireless and Mobile Networks6-101 Mobile Switching Center VLR old BSS GSM: handoff with common MSC 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

102 6: Wireless and Mobile Networks6-102 home network Home MSC PSTN correspondent MSC anchor MSC MSC (a) before handoff GSM: handoff between MSCs r anchor MSC: first MSC visited during call m call remains routed through anchor MSC r new MSCs add on to end of MSC chain as mobile moves to new MSC r IS-41 allows optional path minimization step to shorten multi-MSC chain

103 6: Wireless and Mobile Networks6-103 home network Home MSC PSTN correspondent MSC anchor MSC MSC (b) after handoff GSM: handoff between MSCs r anchor MSC: first MSC visited during call m call remains routed through anchor MSC r new MSCs add on to end of MSC chain as mobile moves to new MSC r IS-41 allows optional path minimization step to shorten multi-MSC chain

104 6: Wireless and Mobile Networks6-104 Mobility: GSM versus Mobile IP GSM elementComment on GSM elementMobile IP element Home systemNetwork to which mobile users 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 SystemNetwork 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 to/from mobile nodes in cells associated with MSC. VLR: temporary database entry in visited system, containing subscription information for each visiting mobile user Foreign agent 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-of- address

105 6: Wireless and Mobile Networks6-105 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

106 6: Wireless and Mobile Networks6-106 Chapter 6 Summary Wireless r wireless links: m capacity, distance m channel impairments m CDMA r IEEE (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 home, visited networks m direct, indirect routing m care-of-addresses r case studies m mobile IP m mobility in GSM r impact on higher-layer protocols

107 6: Wireless and Mobile Networks6-107 Code Division Multiple Access (CDMA) r used in several wireless broadcast channels (cellular, satellite, etc) standards r unique code assigned to each user; i.e., code set partitioning r all users share same frequency, but each user has own chipping sequence (i.e., code) to encode data r encoded signal = (original data) X (chipping sequence) r decoding: inner-product of encoded signal and chipping sequence r allows multiple users to coexist and transmit simultaneously with minimal interference (if codes are orthogonal)

108 6: Wireless and Mobile Networks6-108 CDMA Encode/Decode slot 1 slot 0 d 1 = Z i,m = d i. c m d 0 = slot 0 channel output slot 1 channel output channel output Z i,m sender code data bits slot 1 slot 0 d 1 = -1 d 0 = slot 0 channel output slot 1 channel output receiver code received input D i = Z i,m. c m m=1 M M

109 6: Wireless and Mobile Networks6-109 CDMA: two-sender interference

110 6: Wireless and Mobile Networks6-110 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 S ss (t) A single pulse or symbol of the PN waveform is called a chip

111 6: Wireless and Mobile Networks6-111 S ss (t) ~ m(t)p(t)cos(2 f c t+ ) B: is the bandwidth of m(t)cos(2 f c t+ ) W ss : is the bandwidth of S ss (t) W ss >> B Chip Clock PN Code Generator Oscillator f c S ss (t) Transmitted Signal Data m(t) Phase modulation Block diagram of a DS-SS system with binary phase modulation Transmitter p(t)

112 6: Wireless and Mobile Networks6-112 Channel encoder (A) (B) (C) f(B,C) Symbol duration for m(t): Ts Chip duration for p(t): Tc Processing Gain PG=W ss /B=Ts/Tc, a measure of interference rejection capability Symbol Chip

113 6: Wireless and Mobile Networks6-113 Bit stream (A) Encoded stream (B) Pseudo-noise sequence (C) m(t)m(t) p(t)p(t) Tc Ts

114 6: Wireless and Mobile Networks6-114 r Example: m f(B,C)=B C, where 1 1= = = 0 m if we have received f(B,C) and we are able to re-generate the PN (C), then we can get B.


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