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6: Wireless and Mobile Networks6-1 Chapter 6 Wireless and Mobile Networks A note on the use of these ppt slides: The notes used in this course are substantially.

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Presentation on theme: "6: Wireless and Mobile Networks6-1 Chapter 6 Wireless and Mobile Networks A note on the use of these ppt slides: The notes used in this course are substantially."— Presentation transcript:

1 6: Wireless and Mobile Networks6-1 Chapter 6 Wireless and Mobile Networks A note on the use of these ppt slides: The notes used in this course are substantially based on powerpoint slides developed and copyrighted by J.F. Kurose and K.W. Ross, 2007 Computer Networking: A Top Down Approach 4 th edition. Jim Kurose, Keith Ross Addison-Wesley, July 2007.

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 End-to-end mobility r 6.9 Mobility and higher- layer protocols 6.10 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

11 6: Wireless and Mobile Networks6-11 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

12 6: Wireless and Mobile Networks6-12 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

13 6: Wireless and Mobile Networks6-13 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

14 6: Wireless and Mobile Networks6-14 Exposed Terminal Problem A B C D r B talks to A r C wants to talk to D r C senses channel and finds it to be busy (as B is transmitting to A) r C stays quiet (when it could have ideally transmitted) not possible

15 6: Wireless and Mobile Networks6-15 Hidden and Exposed Terminal Problems r Hidden Terminal m More collisions m Wastage of resources r Exposed Terminal m Underutilization of channel m Lower effective throughput Carrier sense at sender may not prevent collision at receiver

16 6: Wireless and Mobile Networks6-16 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 End-to-end mobility r 6.9 Mobility and higher- layer protocols 6.10 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 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 (SSID) and MAC address m Selects AP to associate with m May perform authentication [Chapter 8] m Will typically run DHCP to get IP address in 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: H1 to selected AP 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: H1 to selected AP

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

23 6: Wireless and Mobile Networks6-23 Avoiding Collisions (more) Idea: allow sender to reserve channel rather than random access of data frames: avoid collisions of long data frames r Sender first transmits small request-to-send (RTS) packets to BS using CSMA m RTSs may still collide with each other (but 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!

24 6: Wireless and Mobile Networks6-24 Collision Avoidance: RTS-CTS Exchange AP A B time RTS(A) RTS(B) RTS(A) CTS(A) DATA (A) ACK(A) reservation collision defer

25 6: Wireless and Mobile Networks6-25 RTS-CTS Exchange r Uses RTS-CTS exchange to avoid hidden terminal problem m Question: how long should sender reserve the channel? m Network Allocation Vector (NAV): each message includes length of time other nodes must wait to send m Any node receiving the RTS cannot transmit for the duration of the transfer m Any node overhearing a CTS cannot transmit for the duration of the transfer

26 6: Wireless and Mobile Networks6-26 CFABED RTS RTS = Request-to-Send RTS-CTS and NAV Pretending a circular range

27 6: Wireless and Mobile Networks6-27 CFABED RTS RTS = Request-to-Send RTS-CTS and NAV NAV = 10 NAV = remaining duration to keep quiet

28 6: Wireless and Mobile Networks6-28 CFABED CTS CTS = Clear-to-Send RTS-CTS and NAV

29 6: Wireless and Mobile Networks6-29 CFABED CTS CTS = Clear-to-Send RTS-CTS and NAV NAV = 8

30 6: Wireless and Mobile Networks6-30 CFABED DATA DATA packet follows CTS Successful data reception acknowledged using ACK RTS-CTS and NAV

31 6: Wireless and Mobile Networks6-31 CFABED ACK RTS-CTS and NAV

32 6: Wireless and Mobile Networks6-32 CFABED ACK RTS-CTS and NAV Reserved area

33 6: Wireless and Mobile Networks6-33 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

34 6: Wireless and Mobile Networks6-34 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

35 6: Wireless and Mobile Networks6-35 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)

36 6: Wireless and Mobile Networks6-36 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

37 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

38 6: Wireless and Mobile Networks6-38 Rate Adaptation r Multiple rates are supported by each wireless standard according to the channel quality m b supports 1M, 2M,5.5M and 11Mbps m g supports 6M,9M,12M,18M,36M,48M,54M r The channel conditions vary m Temporal dimension m Spatial dimension (multiuser diversity) m Each user has independent channel condition r Multiple rates can be exploited to improve the transmission performance m Throughput, latency, etc.

39 6: Wireless and Mobile Networks6-39 A Simple Example A B C D A B C D A B C D T0T0 T1T1 T2T2 Scheme 1: A DA C A B Scheme 2: A BA D A C Of course, scheme 2 is better than scheme 1

40 6: Wireless and Mobile Networks : Advanced Capabilities r Mobile devices are battery powered r Current LAN protocols assume stations are always ready to receive m Idle receive state dominates LAN adapter power consumption over time r How can we power off during idle periods, yet maintain an active session? r Power Management protocol m Allows transceiver to be off as much as possible m Is transparent to existing protocols m Is flexible to support different applications Possible to trade off throughput for battery life Power Management

41 6: Wireless and Mobile Networks6-41 Power Management Approach r Allow idle stations to go to sleep m Stations power save mode stored in AP r APs buffer packets for sleeping stations m AP announces which stations have frames buffered m Traffic Indication Map (TIM) sent with every Beacon r Power saving stations wake up periodically m Listen for Beacons r Time Synchronization Function (TSF) assures AP and power save stations are synchronized m Stations will wake up to hear a Beacon m Synchronization allows extreme low power operation

42 6: Wireless and Mobile Networks6-42 Infrastructure Power Management r Broadcast frames are also buffered in AP m Broadcasts/multicasts are only sent after DTIM m DTIM interval is a multiple of TIM interval r Stations wake up prior to an expected (D)TIM r If TIM indicates frame buffered m Station sends PS-Poll and stays awake to receive data TIM TIM-Interval Time-axis Busy Medium AP activity TIM DTIM DTIM interval Broadcast PS Station Tx operation PS-Poll

43 6: Wireless and Mobile Networks6-43 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

44 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

45 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

46 6: Wireless and Mobile Networks6-46 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 End-to-end mobility r 6.9 Mobility and higher- layer protocols 6.10 Summary

47 6: Wireless and Mobile Networks6-47 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

48 6: Wireless and Mobile Networks6-48 Cellular Networks: the First Hop Two techniques for sharing mobile-to-BS radio spectrum r Combined FDMA/TDMA: divide spectrum in frequency channels, divide each channel into time slots r CDMA: code division multiple access frequency bands time slots

49 6: Wireless and Mobile Networks6-49 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

50 6: Wireless and Mobile Networks6-50 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

51 6: Wireless and Mobile Networks6-51 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 ….. more (and more interesting) cellular topics due to mobility (stay tuned for details)

52 6: Wireless and Mobile Networks6-52 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 Homeless Mobile IP r 6.9 Mobility and higher- layer protocols 6.10 Summary

53 6: Wireless and Mobile Networks6-53 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.

54 6: Wireless and Mobile Networks6-54 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

55 6: Wireless and Mobile Networks6-55 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

56 6: Wireless and Mobile Networks6-56 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?

57 6: Wireless and Mobile Networks6-57 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

58 6: Wireless and Mobile Networks6-58 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

59 6: Wireless and Mobile Networks6-59 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

60 6: Wireless and Mobile Networks6-60 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

61 6: Wireless and Mobile Networks6-61 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

62 6: Wireless and Mobile Networks6-62 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!

63 6: Wireless and Mobile Networks6-63 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

64 6: Wireless and Mobile Networks6-64 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?

65 6: Wireless and Mobile Networks6-65 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)

66 6: Wireless and Mobile Networks6-66 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 End-to-end mobility r 6.9 Mobility and higher- layer protocols 6.10 Summary

67 6: Wireless and Mobile Networks6-67 Mobile IP r RFC 3344 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

68 6: Wireless and Mobile Networks6-68 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

69 6: Wireless and Mobile Networks6-69 Mobile IP: Agent Discovery r Agent advertisement: foreign/home agents advertise service by broadcasting ICMP messages (typefield = 9) R bit: registration required H,F bits: home and/or foreign agent

70 6: Wireless and Mobile Networks6-70 Mobile IP: Registration Example

71 6: Wireless and Mobile Networks6-71 Components of Cellular Network Architecture correspondent MSC wired public telephone network different cellular networks, operated by different providers recall:

72 6: Wireless and Mobile Networks6-72 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

73 6: Wireless and Mobile Networks6-73 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

74 6: Wireless and Mobile Networks6-74 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

75 6: Wireless and Mobile Networks6-75 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

76 6: Wireless and Mobile Networks6-76 home network Home MSC PSTN correspondent MSC anchor MSC MSC (a) before handoff GSM: Handoff between MSCs r Anchor MSC: first MSC visited during cal 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

77 6: Wireless and Mobile Networks6-77 home network Home MSC PSTN correspondent MSC anchor MSC MSC (b) after handoff GSM: Handoff between MSCs r Anchor MSC: first MSC visited during cal 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

78 6: Wireless and Mobile Networks6-78 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

79 6: Wireless and Mobile Networks6-79 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 End-to-end mobility r 6.9 Mobility and higher- layer protocols 6.10 Summary

80 6: Wireless and Mobile Networks6-80 End-to-End Mobility r Re-visit Mobile IP solution m Network centric m Home Agent needs handle not only signaling but also data packets m Network is hard to change r End-to-end mobility m Mobility solution without Home Agent! m Easy to deploy

81 6: Wireless and Mobile Networks6-81 Local Address Translation ConnectionsOld Address and Port Info New Address and Port Info Mapping to Application Conn_A C A A A

82 6: Wireless and Mobile Networks6-82 Transparent to Legacy Applications ConnectionsOld Address and Port Info New Address and Port Info Mapping to Application Conn_A C A B Receives Packet with From A () From A ( ) r Issue r Solution B A A Conn_B

83 6: Wireless and Mobile Networks6-83 Subscribe /Notify service Simultaneous Movements Support A moves from to B moves from to C A A B B

84 6: Wireless and Mobile Networks6-84 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 End-to-end mobility r 6.9 Mobility and higher- layer protocols 6.10 Summary

85 6: Wireless and Mobile Networks6-85 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

86 6: Wireless and Mobile Networks6-86 Chapter 6 Summary Wireless r Wireless links: m Capacity, distance m Channel impairments 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 m End-to-end mobility r Impact on higher-layer protocols


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