Chapter 3: Wireless and Mobile Networks

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1 Computer Network Architectures and Multimedia Guy Leduc Chapter 3 Wireless and Mobile Networks Chapter 7 of Computer Networking: A Top Down Approach, 7 th edition. Jim Kurose, Keith Ross Addison-Wesley, April From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-1 Chapter 3: Wireless and Mobile Networks Background: # wireless (mobile) phone subscribers now exceeds # wired phone subscribers (5-to-1)! # wireless Internet-connected devices exceeds # wireline Internet-connected devices laptops, Internet-enabled phones 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 From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-2 1

2 Chapter 3 outline 3.1 Introduction Wireless 3.2 Wireless links, characteristics CDMA 3.3 IEEE wireless LANs ( Wi-Fi ) 3.4 Cellular Internet Access architecture standards (e.g.3g, LTE) Mobility 3.5 Principles: addressing and routing to mobile users 3.6 Mobile IP 3.7 Handling mobility in cellular s 3.8 Mobility and higherlayer protocols 3.9 Summary From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-3 Elements of a wireless infrastructure From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-4 2

3 Elements of a wireless infrastructure wireless hosts! laptop, smartphone! run applications! may be stationary (non-mobile) or mobile " wireless does not always mean mobility From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-5 Elements of a wireless infrastructure base station! typically connected to wired! relay - responsible for sending packets between wired and wireless host(s) in its area " e.g., cell towers, access points From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-6 3

4 Elements of a wireless 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 From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-7 Characteristics of selected wireless link standards ac Data rate (Mbps) n a,g b a,g point-to-point 4G: LTWE WIMAX 3G: UMTS/WCDMA-HSPDA, CDMA2000-1xEVDO 2.5G: UMTS/WCDMA, CDMA2000 2G: IS-95, CDMA, GSM Indoor 10-30m Outdoor m Mid-range outdoor 200m 4 Km Long-range outdoor 5Km 20 Km From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-8 4

5 Elements of a wireless infrastructure infrastructure mode! base station connects mobiles into wired! handoff: mobile changes base station providing connection into wired From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-9 Elements of a wireless ad hoc mode no base stations nodes can only transmit to other nodes within link coverage nodes organize themselves into a : route among themselves From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks

6 Wireless taxonomy infrastructure (e.g., APs) no infrastructure single hop 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 another given wireless node (MANET, VANET) From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-11 Chapter 3 outline 3.1 Introduction Wireless 3.2 Wireless links, characteristics CDMA 3.3 IEEE wireless LANs ( Wi-Fi ) 3.4 cellular Internet access architecture standards (e.g., 3G, LTE) Mobility 3.5 Principles: addressing and routing to mobile users 3.6 Mobile IP 3.7 Handling mobility in cellular s 3.8 Mobility and higherlayer protocols 3.9 Summary From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks

7 Wireless Link Characteristics (1) Important differences from wired link decreased signal strength: radio signal attenuates as it propagates through matter (path loss) interference from other sources: standardized wireless 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 at destination at slightly different times make communication across (even a point to point) wireless link much more difficult From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-13 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 throughput SNR may change with mobility: dynamically adapt physical layer (modulation SNR(dB) QAM256 (8 Mbps) QAM16 (4 Mbps) BPSK (1 Mbps) technique, rate) From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-14 BER

8 Wireless characteristics Multiple wireless senders and receivers create additional problems (beyond multiple access): C A B C A B A s signal strength C s signal strength Hidden terminal problem B, A hear each other B, C hear each other A, C cannot hear each other; means A, C unaware of their interference at B space Signal attenuation: B, A hear each other B, C hear each other A, C cannot hear each other interfering at B From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-15 Code Division Multiple Access (CDMA) 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 allows multiple users to coexist and transmit simultaneously with minimal interference (if codes are orthogonal : their inner-product = 0) encoded signal = (original data) X (chipping sequence) decoding: inner-product of encoded signal and chipping sequence From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks

9 CDMA Encode/Decode sender data bits code d 0 = 1 d 1 = slot 1 slot 0 Z i,m = d i. cm channel output Z i,m slot 1 channel output slot 0 channel output M received input receiver code slot 1 slot 0 D i = Σ Z. i,m c m=1 m M d 1 = -1 slot 1 channel output d 0 = 1 slot 0 channel output From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-17 CDMA: two-sender interference channel sums together transmissions by sender 1 and 2 using same code as sender 1, receiver recovers sender 1 s original data from summed channel data! From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks

10 Chapter 3 outline 3.1 Introduction Wireless 3.2 Wireless links, characteristics CDMA 3.3 IEEE wireless LANs ( Wi-Fi ) 3.4 cellular Internet access architecture standards (e.g., 3G, LTE) Mobility 3.5 Principles: addressing and routing to mobile users 3.6 Mobile IP 3.7 Handling mobility in cellular s 3.8 Mobility and higherlayer protocols 3.9 Summary From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-19 IEEE Wireless LAN b GHz unlicensed spectrum up to 11 Mbps direct sequence spread spectrum (DSSS) in physical layer all hosts use same chipping code a 5-6 GHz range up to 54 Mbps g GHz range up to 54 Mbps n MIMO (multiple antennas) GHz and 5-6 GHz ranges up to 200 Mbps ac MIMO 5-6 GHz range up to 1.3 Gbps all use CSMA/CA for multiple access all have base-station and ad-hoc versions From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks

11 LAN architecture BSS 1 Internet switch or router wireless host 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 BSS 2 From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks : Channels, association 2.4GHz-2.485GHz spectrum divided into 13 overlapping channels in Europe (11 in USA, 14 in Japan) at different frequencies (bandwidth of 20 MHz each) AP admin chooses channel for AP Typically channels 1, 6 or 11, which do not overlap interference possible: channel can be same as that chosen by neighboring AP! 5-6GHz spectrum divided into 19 non overlapping channels in Europe (25 in USA) 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 From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks

12 802.11: passive/active scanning BBS 1 BBS 2 BBS 1 BBS 2 AP AP 2 AP AP 2 H1 H1 passive scanning: (1) beacon frames sent from APs (2) association Request frame sent: H1 to selected AP (3) association Response frame sent from selected AP to H1 active scanning: (1) Probe Request frame broadcast from H1 (2) Probe Response frames sent from APs (3) Association Request frame sent: H1 to selected AP (4) Association Response frame sent from selected AP to H1 From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-23 IEEE : multiple access avoid collisions: 2 + nodes transmitting at same time : CSMA - sense before transmitting don t collide with ongoing transmission by other node : 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) C A B C A B A s signal strength C s signal strength From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-24 space 12

13 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 DIFS sender data ACK receiver SIFS - if frame received OK return ACK after SIFS (ACK needed due to hidden terminal problem) From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-25 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) frames 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 frames! From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks

14 Collision Avoidance: RTS-CTS exchange A AP B RTS(A) RTS(B) reservation collision RTS(A) CTS(A) CTS(A) DATA (A) defer time ACK(A) ACK(A) From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks frame: addressing frame control duration address 1 address 2 address 3 seq control address 4 payload CRC Address 1: MAC address of wireless host or AP to receive this frame Address 2: MAC address of wireless host or AP transmitting this frame Address 3: MAC address of router interface to which AP is attached Address 4: used only in ad hoc mode From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks

15 frame: addressing (2) H1 R1 router Internet R1 MAC addr H1 MAC addr dest. address source address frame AP MAC addr H1 MAC addr R1 MAC addr The AP is transparent for the router, as a address 1 address 2 address 3 classical layer-2 bridge The AP is not transparent for the host frame From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks frame: addressing (3) H1 R1 router Internet H1 MAC addr AP MAC addr R1 MAC addr address 1 address 2 address 3 wireless dest. add. wireless source add frame The AP is not transparent for the host H1 MAC addr R1 MAC addr dest. address source address frame The AP is transparent for the router, as a classical layer-2 bridge From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks

16 frame: more duration of reserved transmission time (RTS/CTS) frame seq # (for reliable data transfer) frame control duration address 1 address 2 address 3 seq control address 4 payload CRC Protocol To From More Power More Type Subtype Retry WEP Rsvd version AP AP frag mgt data frame type (RTS, CTS, ACK, data) From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks : mobility within same subnet H1 remains in same IP subnet: IP address can remain same switch: which AP is associated with H1? self-learning: switch will see frame from H1 and remember which switch port can be used to reach H1 BBS 1 H1 BBS 2 From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks

17 802.11: advanced capabilities Rate Adaptation 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) operating point BER SNR(dB) 1. SNR decreases, BER increases as node moves away from base station 2. When BER becomes too high, switch to lower transmission rate but with lower BER From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks : advanced capabilities (2) 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 waiting to be sent; otherwise sleep again until next beacon frame (100 ms) Mobile can be asleep 99% of the time! From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks

18 802.15: Personal Area Network (PAN) 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 : evolved from Bluetooth specification GHz radio band (TDM) FHSS: Frequency Hopping up to 4 Mbps S M S P S P M P S P Master device Piconet radius of coverage P Slave device (up to 7) Parked device (inactive) From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-35 Chapter 3 outline 3.1 Introduction Wireless 3.2 Wireless links, characteristics CDMA 3.3 IEEE wireless LANs ( wi-fi ) 3.4 Cellular Internet Access architecture standards (e.g., 3G, LTE) Mobility 3.5 Principles: addressing and routing to mobile users 3.6 Mobile IP 3.7 Handling mobility in cellular s 3.8 Mobility and higherlayer protocols 3.9 Summary From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks

19 Components of cellular architecture cell # covers geographical region # base station (BS) analogous to AP # mobile users attach to through BS # air-interface: physical and link layer protocol between mobile and BS # connects cells to wide area net # manages call setup (more later!) # handles mobility (more later!) Mobile Switching Center Mobile Switching Center Public telephone, and Internet wired From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-37 Cellular s: the first hop Techniques for sharing mobile-to-bs radio spectrum combined FDMA/TDMA: divide spectrum in frequency channels, divide each channel into time slots CDMA: code division multiple access frequency bands time slots From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks

20 2G (voice) architecture (GSM) Base station system (BSS) BTS BSC G Gateway Public telephone Legend Base transceiver station (BTS) Combined FDMA/TDMA o 200 khz frequency bands o Each band supporting 8 slots o Encoding at 13 kbps or 12.2 kbps Base station controller (BSC) Mobile Switching Center () Mobile subscribers From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks G (voice+data) architecture (1) UMTS = Universal Mobile Telecommunications Service radio controller (RNC) G Gateway Public telephone Key insight: new cellular data operates in parallel (except at edge) with existing cellular voice # voice unchanged in core # data operates in parallel SGSN G GGSN Public Internet Serving GPRS Support Node (SGSN) Gateway GPRS Support Node (GGSN) From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks

21 3G (voice+data) architecture (2) radio controller (RNC) G Gateway Public telephone CDMA within TDMA slots over multiple frequencies (FDMA) All schemes combined! promises rates up to 14 Mbps radio interface (WCDMA, HSPA) radio access Universal Terrestrial Radio Access Network (UTRAN) SGSN core General Packet Radio Service (GPRS) Core Network G GGSN Public Internet public Internet From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks G versus 4G architecture 3G 4G-LTE radio controller MME SGSN HSS G Public telephone Gateway G GGSN Public Internet G G Public Internet radio access Universal Terrestrial Radio Access Network (UTRAN) Evolved Packet Core (EPC) S-GW P-GW From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks

22 4G: differences from 3G # all IP core: IP packets tunneled (through core IP ) from base station to gateway # no separation between voice and data all traffic carried over IP core to gateway UE (user element) enodeb (base station) radio access Universal Terrestrial Radio Access Network (UTRAN) Mobility Management Entity (MME) control data Home Subscriber Server (HSS) Serving Gateway HSS (S-GW) MME Evolved Packet Core (EPC) S-GW P-GW Public Internet From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-43 G G Packet data Gateway (P-GW) 4G: LTE (Long-Term Evolution) LTE Radio Access Network Combination of FDMA and TDMA: OFDM " 0.5 ms time slots, frame is one or more slots Uses MIMO antennas Up to 100 Mbps downstream, and 50Mbps upstream, when using 20 MHz worth of wireless spectrum enodeb: similar to RNC in 3G and base station in 2G S-GW (Serving Gateway): similar to SGSN in 3G and in 2G o Data plane mobility anchor point o Performs charging/billing functions and lawful traffic interception P-GW (Packet Data Network Gateway): similar to GGSN in 3G and G- in 2G o Allocates IP addresses to UEs, performs QoS enforcement # Mobility management (see later) o MME: Mobility Management Entity o HSS: Home Subscriber Server (HLR, VLR combined) From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks

23 Radio + Tunneling: UE enodeb P-GW IP packet from UE encapsulated in GPRS Tunneling Protocol (GTP) message at ENodeB GTP message encapsulated in UDP, then encapsulated in IP. Large IP packet addressed to S-GW UE enodeb G S-GW G P-GW tunnel link-layer radio net Wireless and Mobile Networks 7-45 From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-45 Quality of Service in LTE " QoS from enodeb to SGW: min and max guaranteed bit rate (GBR) " QoS in radio access : one of 12 QCI values From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks

24 Chapter 3 outline 3.1 Introduction Wireless 3.2 Wireless links, characteristics CDMA 3.3 IEEE wireless LANs ( Wi-Fi ) 3.4 Cellular Internet Access architecture standards (e.g., 3G, LTE) Mobility 3.5 Principles: addressing and routing to mobile users 3.6 Mobile IP 3.7 Handling mobility in cellular s 3.8 Mobility and higherlayer protocols 3.9 Summary From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-47 What is mobility? spectrum of mobility, from the perspective: no mobility high mobility mobile wireless user, using same access point mobile user, connecting/ disconnecting from using DHCP mobile user, passing through multiple access point while maintaining ongoing connections (like cell phone) From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks

25 Mobility: Vocabulary home : permanent home of mobile (e.g., /24) home agent: entity that will perform mobility functions on behalf of mobile, when mobile is remote Permanent address: address in home, can always be used to reach mobile e.g., wide area From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-49 Mobility: more vocabulary Permanent address: remains constant (e.g., ) visited : in which mobile currently resides (e.g., /24) Care-of-address: address in visited (e.g., ) correspondent: wants to communicate with mobile wide area foreign agent: entity in visited that performs mobility functions on behalf of mobile From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks

26 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 she is? social s! From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-51 Mobility: approaches Let routing handle it: routers advertise permanent address of mobile-nodes-in-residence via usual routing protocols (IGP and BGP): routing tables indicate where each mobile (/32) is 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 From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks

27 Mobility: approaches Let routing handle it: routers advertise permanent address of mobile-nodes-in-residence not via usual routing protocols (IGP scalable and BGP): to millions of routing tables indicate mobiles where each mobile (/32) is 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 From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-53 Mobility: registration home visited wide 2 area foreign agent contacts home agent: this mobile is resident in my 1 mobile contacts foreign agent on entering visited end result: foreign agent knows about mobile home agent knows location of mobile From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks

28 Mobility via Indirect Routing home home agent intercepts packets, forwards to foreign agent foreign agent receives packets, forwards to mobile 3 visited correspondent addresses packets using home address of mobile 1 wide area 2 From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks mobile replies directly to correspondent (using home address as source: issue?) 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 In IPv6: one care-of-address per mobile is possible In IPv4: typically one care-of-address per foreign agent Triangle routing: correspondent-home--mobile inefficient when correspondent and mobile are in the same area From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks

29 Indirect Routing: moving between s suppose mobile user moves to another registers with new foreign agent new foreign agent registers with home agent home agent updates care-of-address for mobile packets continue to be forwarded to mobile (but with new care-of-address) mobility, changing foreign s transparent: on-going connections can be maintained! From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-57 Mobility via Direct Routing correspondent forwards to foreign agent foreign agent receives packets, forwards to mobile visited home correspondent requests, receives foreign address of mobile mobile replies directly to correspondent From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks

30 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? From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-59 Accommodating mobility with direct routing anchor foreign agent: FA in first visited data always routed first to anchor FA when mobile moves: new FA arranges to have data forwarded from old FA (chaining) correspondent wide area 1 correspondent agent anchor foreign agent new foreign agent foreign net visited at session start 2 new foreign From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks

31 Chapter 3 outline 3.1 Introduction Wireless 3.2 Wireless links, characteristics CDMA 3.3 IEEE wireless LANs ( Wi-Fi ) 3.4 Cellular Internet Access architecture standards (e.g., 3G, LTE) Mobility 3.5 Principles: addressing and routing to mobile users 3.6 Mobile IP 3.7 Handling mobility in cellular s 3.8 Mobility and higherlayer protocols 3.9 Summary From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-61 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 From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks

32 Mobile IP: indirect routing packet sent by home agent to foreign agent: a packet within a packet dest: dest: Needs MAC address of mobile when packet is encapsulated foreign-agent-to-mobile packet dest: Permanent address: dest: packet sent by correspondent Care-of address: (here assigned to agent) From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-63 Mobile IP: agent discovery agent advertisement: foreign/home agents (in routers) advertise service by broadcasting ICMP messages (typefield = 9) H,F bits: home and/ or foreign agent type = 9 code = 0 = 9 router address checksum = 9 standard ICMP fields R bit: registration required type = 16 registration lifetime length sequence # RBHFMGV bits 0 or more care-ofaddresses reserved mobility agent advertisement extension From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks

33 Mobile IP: registration example home agent HA: Binds COA and MA time Records mobile agent (MA, HA, MAC address) registration req. COA: HA: MA: Lifetime: 9999 identification: 714 encapsulation format. registration reply HA: MA: Lifetime: 4999 Identification: 714 encapsulation format. visited : /24 foreign agent COA: ICMP agent adv. COA: registration req. COA: HA: MA: Lifetime: 9999 identification:714. registration reply HA: MA: Lifetime: 4999 Identification: 714. mobile agent MA: Sent to well-known port From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-65 Chapter 3 outline 3.1 Introduction Wireless 3.2 Wireless links, characteristics CDMA 3.3 IEEE wireless LANs ( Wi-Fi ) 3.4 Cellular Internet Access architecture standards (e.g., 3G, LTE) Mobility 3.5 Principles: addressing and routing to mobile users 3.6 Mobile IP 3.7 Handling mobility in cellular s 3.8 Mobility and higherlayer protocols 3.9 Summary From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks

34 Components of cellular architecture recall: wired public telephone correspondent different cellular s, operated by different providers From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-67 Handling mobility in cellular s home : of cellular provider you subscribe to (e.g., Proximus, Mobistar, Base) home location register (HLR): database in home containing permanent cell phone #, profile information (services, preferences, billing), information about current location (could be in another ) visited : in which mobile currently resides visitor location register (VLR): database with entry for each user currently in could be home From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks

35 GSM: indirect routing to mobile home consults HLR, gets roaming number of mobile in visited mobile user HLR 2 home home Mobile Switching Center VLR Mobile Switching Center 4 visited correspondent 1 call routed to home Public switched telephone From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks home sets up 2 nd leg of call to in visited in visited completes call through base station to mobile GSM: handoff with common old BSS VLR Mobile Switching Center old routing new routing new BSS Handoff goal: route call via new base station (without interruption) reasons for handoff: 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: signal deteriorates, and/or cell becomes overloaded From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks

36 GSM: handoff with common old BSS VLR Mobile Switching Center new BSS 1. old BSS informs of impending handoff, provides list of 1 + new BSSs 2. sets up path (allocates resources) to new BSS 3. new BSS allocates radio channel for use by mobile 4. new BSS signals, old BSS: ready 5. old BSS tells mobile: perform handoff to new BSS 6. mobile and new BSS: signal to activate new channel 7. mobile signals via new BSS to : handoff complete. reroutes call 8. -old-bss resources released From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-71 GSM: handoff between s (in the same ) home Home anchor correspondent PSTN anchor : first visited during call call remains routed through anchor new s add on to end of chain as mobile moves to new (a) before handoff From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks

37 GSM: handoff between s (2) home Home anchor correspondent PSTN optional path minimization step to shorten multi- chain (b) after handoff From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-73 Handling mobility in LTE: control plane # MME: Mobility Management Entity o performs connection and mobility management on behalf of the UE o receives UE subscription info from the HHS # HSS: Home Subscriber Server (HLR, VLR combined) o Contains UE information including roaming access capabilities, QoS profiles, and authentication info # Paging: idle UE may move from cell to cell: does not know where the idle UE is resident o Paging message from MME broadcast by all enodeb to locate UE # handoff: similar to 3G: o preparation phase o execution phase o completion phase source MME old enodeb old routing P-GW new routing new enodeb From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-74 UE target MME 37

38 Mobility: GSM versus Mobile IP GSM element Comment on GSM element Mobile IP element Home system Gateway Mobile Switching Center, or home. Home Location Register (HLR) Visited System Visited Mobile services Switching Center. Visitor Location Record (VLR) Mobile Station Roaming Number (MSRN), or roaming number Network to which mobile user s permanent phone number belongs Home : 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 Network other than home system where mobile user is currently residing Visited : responsible for setting up calls to/from mobile nodes in cells associated with. VLR: temporary database entry in visited system, containing subscription information for each visiting mobile user Routable address for telephone call segment between home and visited, visible to neither the mobile nor the correspondent. Home Home agent Visited Foreign agent Care-ofaddress From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-75 Chapter 3 outline 3.1 Introduction Wireless 3.2 Wireless links, characteristics CDMA 3.3 IEEE wireless LANs ( Wi-Fi ) 3.4 Cellular Internet Access architecture standards (e.g., 3G, LTE) Mobility 3.5 Principles: addressing and routing to mobile users 3.6 Mobile IP 3.7 Handling mobility in cellular s 3.8 Mobility and higherlayer protocols 3.9 Summary From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks

39 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 unnecessarily delay impairments for real-time traffic limited bandwidth of wireless links From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks 3-77 Chapter 3 Summary Wireless wireless links: capacity, distance channel impairments CDMA IEEE ( Wi-Fi ) CSMA/CA reflects wireless channel characteristics cellular access architecture standards (e.g., 3G, LTE) Mobility principles: addressing, routing to mobile users home, visited s direct, indirect routing care-of-addresses case studies mobile IP mobility in GSM, LTE impact on higher-layer protocols From Computer Networking, by Kurose&Ross 3: Wireless and Mobile Networks

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