Chapter 7 Wireless and Mobile Networks PDF

Chapter 7 Wireless and Mobile Networks A note on the use of these Powerpoint slides: We’re making these slides freely available to all (faculty, students, readers). They’re in PowerPoint form so you see the animations; and can add, modify, and delete slides (including this one) and slide content to...

Chapter 7 Wireless and Mobile Networks A note on the use of these Powerpoint slides: We’re making these slides freely available to all (faculty, students, readers). They’re in PowerPoint form so you see the animations; and can add, modify, and delete slides (including this one) and slide content to suit your needs. Computer They obviously represent a lot of work on our part. In return for use, we only ask the following:  If you use these slides (e.g., in a class) that you mention their source (after all, we’d like people to use our book!) Networking: A Top  If you post any slides on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this Down Approach material. 7th edition Thanks and enjoy! JFK/KWR Jim Kurose, Keith Ross All material copyright 1996-2016 Pearson/Addison Wesley J.F Kurose and K.W. Ross, All Rights Reserved April 2016 Wireless and Mobile Networks 7-1 Ch. 6: Wireless and Mobile Networks Background:  # wireless (mobile) phone subscribers now exceeds # wired phone subscribers (5-to- 1)!  # wireless Internet-connected devices equals # 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 network Wireless and Mobile Networks 7-2 Chapter 7 outline 7.1 Introduction Mobility Wireless 7.5 Principles: addressing and 7.2 Wireless links, routing to mobile characteristics users CDMA 7.6 Mobile IP 6.73 IEEE 802.11 wireless LANs (“Wi- 7.7 Handling mobility in Fi”) cellular networks 67.4 Cellular Internet 7.8 Mobility and higher- Access layer protocols architecture standards (e.g., 3G, LTE) Wireless and Mobile Networks 7-3 Elements of a wireless network wireless hosts  laptop, smartphone  run applications  may be stationary (non-mobile) or network mobile infrastructure wireless does not always mean mobility Wireless and Mobile Networks 7-5 Elements of a wireless network base station  typically connected to wired network  relay - responsible for sending packets between wired network network and infrastructure wireless host(s) in its “area” e.g., cell towers, 802.11 access points Wireless and Mobile Networks 7-6 Elements of a wireless network wireless link  typically used to connect mobile(s) to base station  also used as backbone link network  multiple access infrastructure protocol coordinates link access  various data rates, transmission distance Wireless and Mobile Networks 7-7 Characteristics of selected wireless links 1300 802.11 ac 450 802.11n 54 802.11a,g 802.11a,g point-to-point Data rate (Mbps) 5-11 802.11b 4G: LTWE WIMAX 4 3G: UMTS/WCDMA-HSPDA, CDMA2000-1xEVDO 1 802.15.384 2.5G: UMTS/WCDMA, CDMA2000.056 2G: IS-95, CDMA, GSM Indoor Outdoor Mid-range Long-range 10-30m 50-200m outdoor outdoor 200m – 4 Km 5Km – 20 Km Wireless and Mobile Networks 7-8 Elements of a wireless network infrastructure mode  base station connects mobiles into wired network network  handoff: mobile infrastructure changes base station providing connection into wired network Wireless and Mobile Networks 7-9 Elements of a wireless network ad hoc mode  no base stations  nodes can only transmit to other nodes within link coverage  nodes organize themselves into a network: route among themselves Wireless and Mobile Networks 7-10 Wireless network taxonomy single hop multiple hops host connects to host may have to infrastructure base station (WiFi, relay through several WiMAX, cellular) wireless nodes to (e.g., APs) which connects to connect to larger larger Internet Internet: mesh net no base station, no connection to larger no no base station, no Internet. May have to infrastructure connection to larger relay to reach other Internet (Bluetooth, a given wireless node ad hoc nets) MANET, VANET Wireless and Mobile Networks 7-11 Chapter 7 outline 7.1 Introduction Mobility Wireless 7.5 Principles: addressing and 7.2 Wireless links, routing to mobile characteristics users CDMA 7.6 Mobile IP 7.3 IEEE 802.11 wireless LANs (“Wi- 7.7 Handling mobility in Fi”) cellular networks 7.4 Cellular Internet 7.8 Mobility and higher- Access layer protocols architecture standards (e.g., 3G, LTE) Wireless and Mobile Networks 7-12 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 network frequencies (e.g., 2.4 GHz) shared by other devices (e.g., phone); devices (motors) interfere as well  multipath propagation: radio signal reflects off objects ground, arriving at destination at slightly different times …. make communication across (even a point to point) wireless link much more Wireless “difficult” and Mobile Networks 7-13 Wireless Link Characteristics (2)  SNR: signal-to-noise 10-1 ratio 10-2 larger SNR – easier to extract signal from 10-3 noise (a “good thing”) BER 10-4  SNR versus BER tradeoffs 10-5 given physical layer: 10-6 increase power -> increase SNR->decrease 10-7 10 20 30 BER 40 SNR(dB) given SNR: choose physical layer that meets QAM256 (8 Mbps) BER requirement, giving highest thruput QAM16 (4 Mbps) SNR may change with BPSK (1 Mbps) mobility: dynamically adapt physical layer Wireless and Mobile Networks 7-14 https://documentation.meraki.com/MR/WiFi_Basics_and_Best_Practices/Wireless_fundamentals %3A_Signal-to-Noise_Ratio_(SNR)__and_wireless_signal_strength 15 Wireless network characteristics Multiple wireless senders and receivers create additional problems (beyond multiple access): A B C C A’s signal C’s signal B strength strength A space Hidden terminal problem  B, A hear each other Signal attenuation:  B, C hear each other  B, A hear each other  A, C can not hear each  B, C hear each other other means A, C  A, C can not hear each unaware of their other interfering at B interference at B Wireless and Mobile Networks 7-16 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”)  encoded signal = (original data) X (chipping sequence)  decoding: inner-product of encoded signal and chipping sequence Wireless and Mobile Networks 7-17 CDMA encode/decode channel output Zi,m Zi,m= di.cm data d0 = 1 1 1 1 1 1 1 1 1 d1 = -1 bits -1 -1 -1 -1 -1 -1 -1 -1 sender 1 1 1 1 1 1 1 slot 1 slot 0 code 1 channel channel -1 -1 -1 -1 -1 -1 -1 -1 output output slot 1 slot 0 M Di = S Zi,m.cm m=1 M received 1 1 1 1 1 1 1 1 d0 = 1 input -1 -1 -1 -1 -1 -1 -1 -1 d1 = -1 1 1 1 1 1 1 1 slot 1 slot 0 code 1 channel channel -1 -1 -1 -1 -1 -1 -1 -1 receiver output output slot 1 slot 0 Wireless and Mobile Networks 7-18 CDMA: two-sender interference channel sums together transmissions by Sender 1 sender 1 and 2 Sender 2 using same code as sender 1, receiver recovers sender 1’s original data from summed channel data! Wireless and Mobile Networks 7-19 Chapter 7 outline 7.1 Introduction Mobility Wireless 7.5 Principles: addressing and 7.2 Wireless links, routing to mobile characteristics users CDMA 7.6 Mobile IP 7.3 IEEE 802.11 wireless LANs (“Wi- 7.7 Handling mobility in Fi”) cellular networks 7.4 Cellular Internet 7.8 Mobility and higher- Access layer protocols architecture standards (e.g., 3G, LTE) Wireless and Mobile Networks 7-20  IEEE 802.11 Wireless LAN 802.11b 802.11a  2.4-5 GHz unlicensed  5-6 GHz range spectrum  up to 54 Mbps  up to 11 Mbps 802.11g  direct sequence spread  2.4-5 GHz range spectrum (DSSS) in  up to 54 Mbps physical layer 802.11n: multiple all hosts use same antennae chipping code  2.4-5 GHz range  up to 200 Mbps  all use CSMA/CA for multiple access  Strength of signal received is typically small compared to strength transmitted, so it is COSTLY to build an adapter that can detect collisions Wireless and Mobile Networks 7-21 802.11 LAN architecture  wireless host communicates with Internet base station base station = access point (AP)  Basic Service Set hub, switch (BSS) (aka “cell”) in or router infrastructure mode contains: BSS 1 wireless hosts access point (AP): base station ad hoc mode: hosts BSS 2 only Wireless and Mobile Networks 7-22 802.11: Channels, association  802.11b: 2.4GHz-2.485GHz spectrum divided into 11 channels at different frequencies AP admin chooses frequency for AP interference possible: channel can be same as that chosen by neighboring AP! 2 channels are non-overlapping IFF they are separated by 4 or more channels  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 [Chapter 8] will typically run DHCP to get IP address in AP’s subnet Wireless and Mobile Networks 7-23 Channel Interference starbucks M&P McDonalds https://www.metageek.com/training/resources/why-channels-1-6-11.html Wireless, Mobile Networks 6-24 Non Overlapping Channels https://www.metageek.com/training/resources/why-channels-1-6-11.html Wireless, Mobile Networks 6-25  802.11: passive/active scanning BBS 1 BBS 2 BBS 1 BBS 2 1 1 1 2 2 AP 2 AP 1 AP 2 AP 1 2 3 3 4 H1 H1 passive scanning: active scanning: (1)beacon frames sent from APs (1) Probe Request frame broadcast (2)association Request frame from H1 sent: H1 to selected AP (2) Probe Response frames sent (3)association Response frame from APs sent from selected AP to H1 (3) Association Request frame sent: H1 to selected AP (4) Association Response frame sent from selected AP to H1 Wireless and Mobile Networks 7-26 IEEE 802.11: multiple access  avoid collisions: 2+ nodes transmitting at same time  802.11: CSMA - sense before transmitting don’t collide with ongoing transmission by other node  802.11: no collision detection! difficult to receive (sense collisions) when transmitting due to weak received signals (fading) can’t sense all collisions in any case: hidden terminal, fading goal: avoid collisions: CSMA/C(ollision)A(voidance) A B C C A’s signal C’s signal B strength A strength space Wireless and Mobile Networks 7-27 IEEE 802.11 MAC Protocol: CSMA/CA 802.11 sender 1 if sense channel idle for DIFS then transmit entire frame (no CD) sender receiver 2 if sense channel busy then start random backoff time DIFS timer counts down while channel idle transmit when timer expires data if no ACK, increase random backoff interval, repeat 2 802.11 receiver SIFS - if frame received OK return ACK after SIFS (ACK needed due to ACK hidden terminal problem) SIFS – Short inter-frame spacing DIFS – Distributed inter-frame spacing Wireless and Mobile Networks 7-28 Avoiding collisions (more) idea: allow sender to “reserve” channel rather than random access of data frames: avoid collisions of long data frames  sender first transmits small request-to-send (RTS) packets to BS using CSMA RTSs may still collide with each other (but they’re short)  BS broadcasts clear-to-send CTS in response to RTS  CTS heard by all nodes sender transmits data frame other stations defer transmissions avoid data frame collisions completely using small reservation packets! Wireless and Mobile Networks 7-29  Collision Avoidance: RTS-CTS exchange A B AP RTS(A) RTS(B) reservation collision RTS(A) CTS(A) CTS(A) DATA (A) defer time ACK(A) ACK(A) Wireless and Mobile Networks 7-30  802.11 frame: addressing 2 2 6 6 6 2 6 0 - 2312 4 frame address address address seq address duration payload CRC control 1 2 3 control 4 Address 4: used Address 1: MAC address only in ad hoc of wireless host or AP mode Address 3: MAC to receive this frame address of router interface to Address 2: MAC addresswhich AP is attached of wireless host or AP transmitting this frame Wireless and Mobile Networks 7-31 802.11 frame: addressing Internet H1 R1 router R1 MAC addr H1 MAC addr dest. address source address 802.3 frame AP MAC addr H1 MAC addr R1 MAC addr address 1 address 2 address 3 802.11 frame Wireless and Mobile Networks 7-32 802.11 frame: more frame seq # duration of reserved (for RDT) transmission time (RTS/CTS) 2 2 6 6 6 2 6 0 - 2312 4 frame address address address seq address duration payload CRC control 1 2 3 control 4 2 2 4 1 1 1 1 1 1 1 1 Protocol To From More Power More Type Subtype Retry WEP Rsvd version AP AP frag mgt data frame type (RTS, CTS, ACK, data) Wireless and Mobile Networks 7-33 802.11: mobility within same subnet  H1 remains in same IP subnet: IP address can remain same  switch: which AP is associated with H1? self-learning (Ch. 5): switch will see frame from H1 BBS 1 H1 BBS 2 and “remember” which switch port can be used to reach H1 Wireless and Mobile Networks 7-34 802.11: advanced capabilities Rate adaptation 10-1  base station, mobile 10-2 dynamically change 10-3 BER transmission rate 10-4 (physical layer 10-5 modulation 10-6 technique) as mobile 10-7 10 20 30 40 moves, SNR varies SNR(dB) 1. SNR decreases, BER increase as node moves QAM256 (8 Mbps) away from base station QAM16 (4 Mbps) BPSK (1 Mbps) 2. When BER becomes too operating point high, switch to lower transmission rate but with lower BER Wireless and Mobile Networks 7-35 802.11: advanced capabilities power management  node-to-AP: “I am going to sleep until next beacon frame” AP knows not to transmit frames to this node node wakes up before next beacon frame (~102.4 ms)  beacon frame: contains list of mobiles with AP-to-mobile frames waiting to be sent node will stay awake if AP-to-mobile frames to be sent; otherwise sleep again until next beacon frame Wireless and Mobile Networks 7-36 802.15: personal area network  less than 10 m diameter  replacement for cables (mouse, keyboard, P S headphones)  ad hoc: no infrastructure P radius of M  master/slaves: coverage slaves request S P S permission to send (to P master) master grants requests  802.15: evolved from M Master device Bluetooth specification S Slave device 2.4-2.5 GHz radio P Parked device (inactive) band up to 721 kbps Wireless and Mobile Networks 7-37 Chapter 7 outline 7.1 Introduction Mobility Wireless 7.5 Principles: addressing and 7.2 Wireless links, characteristics CDMA routing to mobile users 7.3 IEEE 802.11 wireless LANs (“Wi-Fi”) 7.6 Mobile IP 7.4 Cellular Internet access architecture 7.7 Handling mobility in standards (e.g., 3G, LTE) cellular networks 7.8 Mobility and higher- layer protocols Wireless and Mobile Networks 7-38 omponents of cellular network architecture MSC  connects cells to wired tel. net.  manages call setup (more later!)  handles mobility (more later!) cell  covers geographical Mobile region Switching  base station Center Public telephone (BS) analogous network to 802.11 AP  mobile users Mobile attach to Switching network through Center BS  air-interface: wired network physical and link layer protocol Wireless and Mobile Networks between mobile 7-39 Cellular networks: the first hop Two techniques for sharing mobile-to-BS radio spectrum  combined FDMA/TDMA: divide spectrum in frequency channels, time slots divide each channel into time slots  CDMA: code division frequency multiple access bands Wireless and Mobile Networks 7-40 2G (voice) network architecture Base station system (BSS) MSC BTS BSC G Public telephone network Gateway MSC Legend Base transceiver station (BTS) Base station controller (BSC) Mobile Switching Center (MSC) Mobile subscribers Wireless and Mobile Networks 7-41 G (voice+data) network architecture MSC G Public telephone network radio network Gateway controller MSC G Public SGSN Internet Key insight: new cellular data network operates in parallel GGSN (except at edge) with existing cellular voice network Serving GPRS Support Node (SGSN)  voice network unchanged in core  data network operates in parallel Gateway GPRS Support Node (GGSN) Wireless and Mobile Networks 7-42 G (voice+data) network architecture MSC G Public telephone network radio network Gateway controller MSC G Public SGSN Internet GGSN radio interface (WCDMA, HSPA) radio access network core network public Universal Terrestrial Radio General Packet Radio Service Internet Access Network (UTRAN) (GPRS) Core Network Wireless and Mobile Networks 7-43 G versus 4G LTE network architectur MSC G Public telephone network radio Gateway 3G network controller MSC G Public SGSN Internet GGSN HSS 4G-LTE MME G G Public Internet S-GW P-GW radio access network Evolved Packet Core Universal Terrestrial Radio Access Network (UTRAN) (EPC) Wireless and Mobile Networks 7-44 4G: differences from 3G  all IP core: IP packets tunneled (through core IP network) from base station to gateway  no separation between voice and data – all traffic carried over IP core to gateway Mobility Home Subscriber Management Server(HSS) Serving Packet data Entity (MME) (like HLR+VLR) Gateway network UE eNodeB (user element)(base station) HSS (S-GW) Gateway MME (P-GW) control G G Public data Internet S-GW P-GW radio access network Evolved Packet Core Universal Terrestrial Radio Access Network (UTRAN) (EPC) Wireless and Mobile Networks 7-45 unctional split of major LTE components handles idle/active UE transitions pages UE sets up eNodeB-PGW tunnel (aka bearer) holds idle UE info QoS enforcement Wireless and Mobile Networks 7-46 Radio+Tunneling: UE – eNodeB – PGW IP packet from UE GTP message encapsulated in encapsulated in GPRS UDP, then encapsulated in IP. Tunneling Protocol (GTP) large IP packet addressed to message at ENodeB SGW G G UE S-GW eNodeB P-GW tunnel link-layer radio net Wireless and Mobile Networks 7-47 Quality of Service in LTE  QoS from eNodeB to SGW: min and max guaranteed bit rate  QoS in radio access network: one of 12 QCI values Wireless and Mobile Networks 7-48 Chapter 7 outline 7.1 Introduction Mobility Wireless 7.5 Principles: addressing and 7.2 Wireless links, characteristics CDMA routing to mobile users 7.3 IEEE 802.11 wireless LANs (“Wi-Fi”) 7.6 Mobile IP 7.4 Cellular Internet Access architecture 7.7 Handling mobility in standards (e.g., 3G, LTE) cellular networks 7.8 Mobility and higher- layer protocols Wireless and Mobile Networks 7-49 What is mobility?  spectrum of mobility, from the network perspective: no mobility high mobility mobile wireless user, mobile user, mobile user, passing using same access connecting/ through multiple point disconnecting from access point while network using maintaining ongoing DHCP. connections (like cell phone) Wireless and Mobile Networks 7-50  Mobility: vocabulary home network: permanent home agent: entity that will “home” of mobile perform mobility functions on (e.g., 128.119.40/24) behalf of mobile, when mobile is remote wide area network permanent address: address in home network, can always be used to reach mobile e.g., 128.119.40.186 Wireless and Mobile Networks 7-51 Mobility: more vocabulary permanent address: remains visited network: network in constant (e.g., 128.119.40.186) which mobile currently resides (e.g., 79.129.13/24) care-of-address: address in visited network. (e.g., 79,129.13.2) wide area network foreign agent: entity in visited network that performs mobility correspondent: wants functions on behalf of to communicate with mobile. mobile Wireless and Mobile Networks 7-52 How do you contact a mobile friend: Consider friend frequently I wonder where changing addresses, how Alice moved to?  do you all search find her? phone books?  call her parents?  expect her to let you know where he/she is?  Facebook! Wireless and Mobile Networks 7-53 Mobility: approaches  let routing handle it: routers advertise permanent address of mobile-nodes-in- residence via usual routing table exchange. routing tables indicate where each mobile located no changes to end-systems  let end-systems handle it: indirect routing: communication from correspondent to mobile goes through home agent, then forwarded to remote direct routing: correspondent gets foreign address of mobile, sends directly to mobile Wireless and Mobile Networks 7-54 Mobility: approaches  let routing handle it: routers advertise permanent address not of mobile-nodes-in- residence via usual scalablerouting table exchange. to millions of routing tablesmobiles indicate where each mobile located no changes to end-systems  let end-systems handle it: indirect routing: communication from correspondent to mobile goes through home agent, then forwarded to remote direct routing: correspondent gets foreign address of mobile, sends directly to mobile Wireless and Mobile Networks 7-55 Mobility: registration visited network home network 1 2 wide area network mobile contacts foreign agent contacts home foreign agent on agent home: “this mobile is entering visited resident in my network” network end result:  foreign agent knows about mobile  home agent knows location of mobile Wireless and Mobile Networks 7-56 Mobility via indirect routing foreign agent receives packets, home agent intercepts forwards to mobile packets, forwards to visited foreign agent network home network 3 wide area network 2 1 correspondent 4 addresses packets mobile replies using home address of directly to mobile correspondent Wireless and Mobile Networks 7-57 Indirect Routing: comments  mobile uses two addresses: permanent address: used by correspondent (hence mobile location is transparent to correspondent) care-of-address: used by home agent to forward datagrams to mobile  foreign agent functions may be done by mobile itself  triangle routing: correspondent-home- network-mobile inefficient when correspondent, mobile are in same network Wireless and Mobile Networks 7-58 Indirect routing: moving between networks  suppose mobile user moves to another network registers with new foreign agent new foreign agent registers with home agent home agent update care-of-address for mobile packets continue to be forwarded to mobile (but with new care-of-address)  mobility, changing foreign networks transparent: on going connections can be maintained! Wireless and Mobile Networks 7-59 Mobility via direct routing foreign agent receives packets, correspondent forwards forwards to mobile to foreign agent visited network home network 3 1 2 4 mobile replies correspondent directly to requests, receives correspondent foreign address of mobile Wireless and Mobile Networks 7-60 Mobility via direct routing: comments  overcome triangle routing problem  non-transparent to correspondent: correspondent must get care-of-address from home agent what if mobile changes visited network? 3 1 2 4 Wireless and Mobile Networks 7-61 Accommodating mobility with direct routing  anchor foreign agent: FA in first visited network  data always routed first to anchor FA  when mobile moves: new FA arranges to have data forwarded from old FA (chaining) foreign net visited at session start anchor foreign wide area agent 2 network 1 4 3 5 new correspondent foreign new foreign agent network correspondent agent Wireless and Mobile Networks 7-62 Chapter 7 outline 7.1 Introduction Mobility Wireless 7.5 Principles: addressing and 7.2 Wireless links, characteristics CDMA routing to mobile users 7.3 IEEE 802.11 wireless LANs (“Wi-Fi”) 7.6 Mobile IP 7.4 Cellular Internet Access architecture 7.7 Handling mobility in standards (e.g., 3G, LTE) cellular networks 7.8 Mobility and higher- layer protocols Wireless and Mobile Networks 7-63 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 Wireless and Mobile Networks 7-64  Mobile IP: indirect routing foreign-agent-to-mobile packet packet sent by home agent to foreign dest: 128.119.40.186 agent: a packet within a packet dest: 79.129.13.2 dest: 128.119.40.186 Permanent address: 128.119.40.186 Care-of address: 79.129.13.2 dest: 128.119.40.186 packet sent by correspondent Wireless and Mobile Networks 7-65  Mobile IP: agent discovery  agent advertisement: foreign/home agents advertise service by broadcasting ICMP messages (typefield = 9) 0 8 16 24 type = 9 code = 0 checksum =9 =9 H,F bits: home and/or standard foreign agent router address ICMP fields R bit: registration required type = 16 length sequence # RBHFMGV registration lifetime reserved bits mobility agent advertisement 0 or more care-of- extension addresses Wireless and Mobile Networks 7-66 Mobile IP: registration example home agent visited network: 79.129.13/24 foreign agent HA: 128.119.40.7 COA: 79.129.13.2 mobile agent MA: 128.119.40.186 ICMP agent adv. COA: 79.129.13.2 …. registration registration req. COA:req. 79.129.13.2 COA: 79.129.13.2 HA: 128.119.40.7 HA: 128.119.40.7 MA: 128.119.40.186 MA: 128.119.40.186 Lifetime: 9999 Lifetime: 9999 identification:714 identification: 714 …. encapsulation format …. registration reply HA: 128.119.40.7 registration MA: 128.119.40.186 reply HA: 128.119.40.7 Lifetime: 4999 MA: 128.119.40.186 Identification: 714 Lifetime: 4999 encapsulation format Identification: 714 …. …. time Wireless and Mobile Networks 7-67 omponents of cellular network architectu recall: correspondent wired public telephone network MSC MSC MSC MSC MSC different cellular networks, operated by different providers Wireless and Mobile Networks 7-68 Handling mobility in cellular networks  home network: network of cellular provider you subscribe to (e.g., Sprint PCS, Verizon) home location register (HLR): database in home network containing permanent cell phone #, profile information (services, preferences, billing), information about current location (could be in another network)  visited network: network in which mobile currently resides visitor location register (VLR): database with entry for each user currently in network could be home network Wireless and Mobile Networks 7-69 GSM: indirect routing to mobile home HLR network correspondent 2 home Mobile home MSC consults HLR, Switching gets roaming number of Center mobile in visited network 1 call routed to home network 3 Public VLR switched Mobile telephone Switching network Center 4 home MSC sets up 2nd leg of call to MSC in visited network mobile user MSC in visited network completes visited call through base station to mobile network Wireless and Mobile Networks 7-70 GSM: handoff with common MSC  handoff goal: route call via new base station (without interruption) VLR Mobile  reasons for handoff: Switching stronger signal to/from Center new BSS (continuing connectivity, less old new routing routing battery drain) old BSS load balance: free up new BSS channel in current BSS GSM doesn't mandate why to perform handoff (policy), only how (mechanism)  handoff initiated by old BSS Wireless and Mobile Networks 7-71  GSM: handoff with common MSC 1. old BSS informs MSC of impending handoff, provides list of 1+ new BSSs 2. MSC sets up path (allocates resources) to new BSS VLR Mobile 3. new BSS allocates radio channel for Switching Center 2 use by mobile 1 4 4. new BSS signals MSC, old BSS: ready 7 8 5. old BSS tells mobile: perform handoff to 3 new BSS old BSS 5 6 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 Wireless and Mobile Networks 7-72 GSM: handoff between MSCs  anchor MSC: first MSC visited during call home network call remains routed correspondent Home through anchor MSC MSC  new MSCs add on to anchor MSC end of MSC chain as PSTN MSC mobile moves to new MSC MSC MSC  optional path minimization step to shorten multi-MSC chain (a) before handoff Wireless and Mobile Networks 7-73 GSM: handoff between MSCs  anchor MSC: first MSC home network visited during call correspondent call remains routed Home MSC through anchor MSC  new MSCs add on to anchor MSC PSTN MSC end of MSC chain as MSC mobile moves to new MSC MSC  optional path minimization step to (b) after handoff shorten multi-MSC chain Wireless and Mobile Networks 7-74 Handling Mobility in LTE  Paging: idle UE may move from cell to cell: network does not know where the idle UE is resident paging message from MME broadcast by all eNodeB to locate UE  handoff: similar source P-GW target MME MME to 3G:  preparation phase  execution phase  completion phase old new old routing routing new eNodeB eNodeB Wireless and Mobile Networks 7-75 Mobility: cellular versus Mobile IP cellular element Comment on cellular element Mobile IP element Home system Network to which mobile user’s permanent Home phone number belongs network Gateway Mobile Home MSC: point of contact to obtain routable Home agent Switching Center, or address of mobile user. HLR: database in “home MSC”. Home home system containing permanent phone Location Register number, profile information, current location of (HLR) mobile user, subscription information Visited System Network other than home system where mobile Visited user is currently residing network Visited Mobile Visited MSC: responsible for setting up calls Foreign agent services Switching to/from mobile nodes in cells associated with Center. MSC. VLR: temporary database entry in visited Visitor Location system, containing subscription information for Record (VLR) each visiting mobile user Mobile Station Routable address for telephone call segment Care-of- Roaming Number between home MSC and visited MSC, visible address (MSRN), or “roaming to neither the mobile nor the correspondent. number” Wireless and Mobile Networks 7-76 Wireless, mobility: impact on higher layer protocols  logically, impact should be minimal … best effort service model remains unchanged TCP and UDP can (and do) run over wireless, mobile  … but performance-wise: packet loss/delay due to bit-errors (discarded packets, delays for link-layer retransmissions), and handoff TCP interprets loss as congestion, will decrease congestion window un-necessarily delay impairments for real-time traffic limited bandwidth of wireless links Wireless and Mobile Networks 7-77 Chapter 7 summary Wireless Mobility  wireless links:  principles: addressing, capacity, distance routing to mobile channel impairments users CDMA home, visited networks  IEEE 802.11 (“Wi-Fi”) direct, indirect routing care-of-addresses CSMA/CA reflects wireless channel characteristics  cellular access  case studies architecture mobile IP standards (e.g., 3G, 4G LTE) mobility in GSM, LTE  impact on higher-layer protocols Wireless and Mobile Networks 7-78