Chapter 7 Wireless and Mobile Networks A note

Chapter 7 Wireless and Mobile Networks A note on the use of these Power. Point slides: We’re making these slides freely available to all (faculty, students, readers). They’re in Power. Point form so you see the animations; and can add, modify, and delete slides (including this one) and slide content to suit your needs. 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!) 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 material. For a revision history, see the slide note for this page. Thanks and enjoy! JFK/KWR All material copyright 1996 -2020 J. F Kurose and K. W. Ross, All Rights Reserved Computer Networking: A Top-Down Approach 8 th edition Jim Kurose, Keith Ross Pearson, 2020

Wireless and Mobile Networks: context § more wireless (mobile) phone subscribers than fixed (wired) phone subscribers (10 -to-1 in 2019)! § more mobile-broadband-connected devices than fixed-broadbandconnected devices (5 -1 in 2019)! • 4 G/5 G cellular networks now embracing Internet protocol stack, including SDN § 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 § Introduction Wireless Mobility § Wireless Links and network characteristics § Wi. Fi: 802. 11 wireless LANs § Cellular networks: 4 G and 5 G § Mobility management: principles § Mobility management: practice • 4 G/5 G networks • Mobile IP § Mobility: impact on higher-layer protocols Wireless and Mobile Networks: 7 - 3

Elements of a wireless network wired network infrastructure Wireless and Mobile Networks: 7 - 4

Elements of a wireless network wireless hosts wired network infrastructure § laptop, smartphone, Io. T § run applications § may be stationary (non-mobile) or mobile • wireless does not always mean mobility! Wireless and Mobile Networks: 7 - 5

Elements of a wireless network base station wired network infrastructure § typically connected to wired network § relay - responsible for sending packets between wired network and wireless host(s) in its “area” • e. g. , cell towers, 802. 11 access points Wireless and Mobile Networks: 7 - 6

Elements of a wireless network wireless link wired network infrastructure § typically used to connect mobile(s) to base station, also used as backbone link § multiple access protocol coordinates link access § various transmission rates and distances, frequency bands Wireless and Mobile Networks: 7 - 7

Characteristics of selected wireless links 14 Gbps 10 Gbps 3. 5 Gbps 600 Mbps 54 Mbps 11 Mbps 2 Mbps 802. 11 ax 5 G 802. 11 ac 802. 11 af, ah 802. 11 n 4 G LTE 802. 11 g 802. 11 b Bluetooth Indoor Outdoor 10 -30 m 50 -200 m Midrange outdoor 200 m-4 Km Long range outdoor 4 Km-15 Km Wireless and Mobile Networks: 7 - 8

Elements of a wireless network wired network infrastructure mode § base station connects mobiles into wired network § handoff: mobile 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 infrastructure (e. g. , APs) host connects to base station (Wi. Fi, cellular) which connects to larger Internet host may have to relay through several wireless nodes to connect to larger Internet: mesh net no infrastructure no base station, no connection to larger Internet (Bluetooth, ad hoc nets) no base station, no connection to larger Internet. May have to relay to reach other a given wireless node MANET, VANET Wireless and Mobile Networks: 7 - 11

Chapter 7 outline § Introduction Wireless Mobility § Wireless links and network characteristics § Wi. Fi: 802. 11 wireless LANs § Cellular networks: 4 G and 5 G § Mobility management: principles § Mobility management: practice • 4 G/5 G networks • Mobile IP § Mobility: impact on higher-layer protocols Link Layer: 6 -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: wireless network frequencies (e. g. , 2. 4 GHz) shared by many devices (e. g. , Wi. Fi, cellular, motors): interference § 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” Wireless and Mobile Networks: 7 - 13

Wireless link characteristics (2) § SNR: signal-to-noise ratio 10 -1 • larger SNR – easier to extract signal from noise (a “good thing”) • 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 technique, rate) 10 -3 BER § SNR versus BER tradeoffs 10 -2 10 -4 10 -5 10 -6 10 -7 10 20 30 40 SNR(d. B) QAM 256 (8 Mbps) QAM 16 (4 Mbps) BPSK (1 Mbps) Wireless and Mobile Networks: 7 - 14

Wireless link characteristics (3) Multiple wireless senders, receivers create additional problems (beyond multiple access): B A C C A B C’s signal strength A’s signal strength space Hidden terminal problem § B, A hear each other § B, C hear each other § A, C can not hear each other means A, C unaware of their interference at B Signal attenuation: § B, A hear each other § B, C hear each other § A, C can not hear each other interfering at B Wireless and Mobile Networks: 7 - 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”) § encoding: inner product: (original data) X (chipping sequence) § decoding: summed inner-product: (encoded data) X (chipping sequence) Wireless and Mobile Networks: 7 - 16

CDMA encode/decode sender data bits code Zi, m= di. cm d 0 = 1 -1 -1 -1 1 1 1 -1 -1 -1 slot 1 channel output 1 -1 1 1 1 d 1 = -1 1 channel output Zi, m -1 -1 -1 slot 0 channel output M Di = S Zi, m. cm m=1 receiver received input 1 1 1 1 code -1 -1 1 1 -1 -1 -1 slot 1 M 1 1 -1 -1 slot 0 d 0 = 1 d 1 = -1 slot 1 channel output slot 0 channel output … but this isn’t really useful yet! Wireless and Mobile Networks: 7 - 17

CDMA: two-sender interference Sender 1 channel sums together transmissions by sender 1 and 2 Sender 2 using same code as sender 1, receiver recovers sender 1’s original data from summed channel data! … now that’s useful! Wireless and Mobile Networks: 7 - 18

Chapter 7 outline § Introduction Wireless Mobility § Wireless links and network characteristics § Wi. Fi: 802. 11 wireless LANs § Cellular networks: 4 G and 5 G § Mobility management: principles § Mobility management: practice • 4 G/5 G networks • Mobile IP § Mobility: impact on higher-layer protocols Link Layer: 6 -19

IEEE 802. 11 Wireless LAN IEEE 802. 11 standard 802. 11 b 802. 11 g 802. 11 n (Wi. Fi 4) Year Max data rate Range Frequency 1999 2003 2009 11 Mbps 54 Mbps 600 30 m 30 m 70 m 2. 4 Ghz 2. 4, 5 Ghz 802. 11 ac (Wi. Fi 5) 2013 3. 47 Gpbs 70 m 5 Ghz 802. 11 ax (Wi. Fi 6) 2020 (exp. ) 14 Gbps 70 m 2. 4, 5 Ghz 802. 11 af 2014 35 – 560 Mbps 1 Km 802. 11 ah 2017 347 Mbps 1 Km unused TV bands (54 -790 MHz) 900 Mhz § all use CSMA/CA for multiple access, and have base-station and ad-hoc network versions Wireless and Mobile Networks: 7 - 20

802. 11 LAN architecture Internet switch or router BSS 1 § 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 Wireless and Mobile Networks: 7 - 21

802. 11: Channels, association § spectrum divided into channels at different frequencies • AP admin chooses frequency for AP • interference possible: channel can be same as that chosen by neighboring AP! § arriving 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 • then may perform authentication [Chapter 8] • then typically run DHCP to get IP address in AP’s subnet BSS Wireless and Mobile Networks: 7 - 22

802. 11: passive/active scanning BBS 1 AP 1 BBS 2 1 1 2 AP 2 3 H 1 passive scanning: (1) beacon frames sent from APs (2) association Request frame sent: H 1 to selected AP (3) association Response frame sent from selected AP to H 1 AP 1 BBS 2 2 1 2 3 AP 2 4 H 1 active scanning: (1) Probe Request frame broadcast from H 1 (2) Probe Response frames sent from APs (3) Association Request frame sent: H 1 to selected AP (4) Association Response frame sent from selected AP to H 1 Wireless and Mobile Networks: 7 - 23

IEEE 802. 11: multiple access § avoid collisions: 2+ nodes transmitting at same time § 802. 11: CSMA - sense before transmitting • don’t collide with detected ongoing transmission by another node § 802. 11: no collision detection! • difficult to sense collisions: high transmitting signal, weak received signal due to fading • can’t sense all collisions in any case: hidden terminal, fading • goal: avoid collisions: CSMA/Collision. Avoidance C A B C C’s signal strength A’s signal strength space Wireless and Mobile Networks: 7 - 24

IEEE 802. 11 MAC Protocol: CSMA/CA 802. 11 sender 1 if sense channel idle for DIFS then transmit entire frame (no CD) 2 if sense channel busy then start random backoff timer counts down while channel idle transmit when timer expires if no ACK, increase random backoff interval, repeat 2 802. 11 receiver sender receiver DIFS data SIFS ACK if frame received OK return ACK after SIFS (ACK needed due to hidden terminal problem) Wireless and Mobile Networks: 7 - 25

Avoiding collisions (more) idea: sender “reserves” channel use for data frames using small reservation packets § sender first transmits small request-to-send (RTS) packet 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 Wireless and Mobile Networks: 7 - 26

Collision Avoidance: RTS-CTS exchange A B AP RTS(B) RTS(A) reservation collision RTS(A) CTS(A) time DATA (A) ACK(A) defer ACK(A) Wireless and Mobile Networks: 7 - 27

802. 11 frame: addressing 2 2 6 6 6 2 6 frame duration address seq address control 1 2 3 4 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 0 - 2312 payload 4 CRC Address 4: used only in ad hoc mode Address 3: MAC address of router interface to which AP is attached Wireless and Mobile Networks: 7 - 28

802. 11 frame: addressing H 1 Internet R 1 802. 3 Ethernet frame R 1 MAC addr H 2 MAC addr MAC dest addr MAC source addr AP MAC addr H 1 MAC addr R 1 MAC address 1 address 2 address 3 802. 11 Wi. Fi frame Wireless and Mobile Networks: 7 - 29

802. 11 frame: addressing duration of reserved transmission time (RTS/CTS) 2 2 6 6 frame sequence # (for reliable data transfer) 6 2 frame duration address seq address control 1 2 3 4 2 protocol version 2 4 1 1 type subtype to AP from AP more frag retry 4 0 - 2312 6 payload 1 1 power more mgt data CRC 1 1 WEP rsvd frame type (RTS, CTS, ACK, data) Wireless and Mobile Networks: 7 - 30

802. 11: mobility within same subnet § H 1 remains in same IP subnet: IP address can remain same § switch: which AP is associated with H 1? • self-learning (Ch. 6): switch will see frame from H 1 and “remember” which switch port can be used to reach H 1 BBS 1 H 1 BBS 2 Wireless and Mobile Networks: 7 - 31

802. 11: advanced capabilities Rate adaptation 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 10 -1 10 -2 BER § base station, mobile dynamically change transmission rate (physical layer modulation technique) as mobile moves, SNR varies 10 -3 10 -4 10 -5 10 -6 10 -7 10 20 30 SNR(d. B) 40 QAM 256 (8 Mbps) QAM 16 (4 Mbps) BPSK (1 Mbps) operating point Wireless and Mobile Networks: 7 - 32

802. 11: advanced capabilities power management § node-to-AP: “I am going to sleep until next beacon frame” • AP knows not to transmit frames to this node • node wakes up before next beacon frame § beacon frame: contains list of mobiles with AP-to-mobile frames waiting to be sent • node will stay awake if AP-to-mobile frames to be sent; otherwise sleep again until next beacon frame Wireless and Mobile Networks: 7 - 33

Personal area networks: Bluetooth § less than 10 m diameter § replacement for cables (mouse, keyboard, headphones) § ad hoc: no infrastructure § 2. 4 -2. 5 GHz ISM radio band, up to 3 Mbps § master controller / clients devices: • master polls clients, grants requests for client transmissions P C P radius of coverage M C P M master device C client device P parked device (inactive) Wireless and Mobile Networks: 7 - 34

Personal area networks: Bluetooth § TDM, 625 msec sec. slot § FDM: sender uses 79 frequency channels in known, pseudo-random order slot-toslot (spread spectrum) • other devices/equipment not in piconet only interfere in some slots § parked mode: clients can “go to sleep” (park) and later wakeup (to preserve battery) § bootstrapping: nodes self-assemble (plug and play) into piconet P C P radius of coverage M C P M master device C client device P parked device (inactive) Wireless and Mobile Networks: 7 - 35

Chapter 7 outline § Introduction Wireless Mobility § Wireless links and network characteristics § Wi. Fi: 802. 11 wireless LANs § Cellular networks: 4 G and 5 G § Mobility management: principles § Mobility management: practice • 4 G/5 G networks • Mobile IP § Mobility: impact on higher-layer protocols Link Layer: 6 -36

4 G/5 G cellular networks § § the solution for wide-area mobile Internet widespread deployment/use: more mobile-broadband-connected devices than fixedbroadband-connected devices (5 -1 in 2019)! • 4 G availability: 97% of time in Korea (90% in US) transmission rates up to 100’s Mbps technical standards: 3 rd Generation Partnership Project (3 GPP) • wwww. 3 gpp. org • 4 G: Long-Term Evolution (LTE)standard • § § Wireless and Mobile Networks: 7 - 37

4 G/5 G cellular networks similarities to wired Internet § edge/core distinction, but both below to same carrier § global cellular network: a network of networks § widespread use of protocols we’ve studied: HTTP, DNS, TCP, UDP, IP, NAT, separation of data/control planes, SDN, Ethernet, tunneling § interconnected to wired Internet differences from wired Internet § different wireless link layer § mobility as a 1 st class service § user “identity” (via SIM card) § business model: users subscribe to a cellular provider • • strong notion of “home network” versus roaming on visited nets global access, with authentication infrastructure, and inter-carrier settlements Wireless and Mobile Networks: 7 - 38

Elements of 4 G LTE architecture Mobile device: § smartphone, tablet, laptop, Io. T, . . . with 4 G LTE radio § 64 -bit International Mobile Subscriber Identity (IMSI), stored on SIM (Subscriber Identity Module) card § LTE jargon: User Equipment (UE) Mobile device (UE) Base station (e. Node-B) Mobility Management Entity (MME) … radio access network Home Subscriber Service (HSS) to Internet PDN gateway (P-GW) Serving Gateway (S-GW) all-IP Enhanced Packet Core (EPC) Wireless and Mobile Networks: 7 - 39

Elements of 4 G LTE architecture Base station: § at “edge” of carrier’s network § manages wireless radio resources, mobile devices in its coverage area (“cell”) § coordinates device authentication with other elements § similar to Wi. Fi AP but: • active role in user mobility • coordinates with nearly base stations to optimize radio use § LTE jargon: e. Node-B Mobile device (UE) Base station (e. Node-B) Mobility Management Entity (MME) … Home Subscriber Service (HSS) to Internet PDN gateway (P-GW) Serving Gateway (S-GW) Wireless and Mobile Networks: 7 - 40

Elements of 4 G LTE architecture Home Subscriber Service § stores info about mobile devices for which the HSS’s network is their “home network” § works with MME in device authentication Mobile device (UE) Base station (e. Node-B) Mobility Management Entity (MME) … Home Subscriber Service (HSS) to Internet PDN gateway (P-GW) Serving Gateway (S-GW) Wireless and Mobile Networks: 7 - 41

Elements of 4 G LTE architecture Serving Gateway (S-GW), PDN Gateway (P-GW) § lie on data path from mobile to/from Internet § P-GW • gateway to mobile cellular network • Looks like nay other internet gateway router • provides NAT services § other routers: • extensive use of tunneling Mobile device (UE) Base station (e. Node-B) Mobility Management Entity (MME) … Home Subscriber Service (HSS) to Internet PDN gateway (P-GW) Serving Gateway (S-GW) Wireless and Mobile Networks: 7 - 42

Elements of 4 G LTE architecture Mobility Management Entity Mobile device (UE) § device authentication (device -to-network, network-todevice) coordinated with mobile home network HSS § mobile device management: • device handover between cells • tracking/paging device location § path (tunneling) setup from mobile device to P-GW Base station (e. Node-B) Mobility Management Entity (MME) … Home Subscriber Service (HSS) to Internet PDN gateway (P-GW) Serving Gateway (S-GW) Wireless and Mobile Networks: 7 - 43

LTE: data plane control plane separation HSS base station MME S-GW S-GW base station IP tunnels control plane § new protocols for mobility management , security, authentication (later) P-GW data plane § new protocols at link, physical layers P-GW § extensive use of tunneling to facilitate mobility Wireless and Mobile Networks: 7 - 44

Link LTE data plane protocol stack: first hop LTE link layer protocols: Application Transport IP IP Packet Data Convergence Radio Link Medium Access Physical § Packet Data Convergence: header compression, encryption § Radio Link Control (RLC) Protocol: fragmentation/reassembly, reliable data transfer § Medium Access: requesting, use of radio transmission slots Physical base station S-GW data plane P-GW Wireless and Mobile Networks: 7 - 45

Link LTE data plane protocol stack: first hop LTE radio access network: Application Transport IP IP Packet Data Convergence Radio Link Medium Access Physical base station § downstream channel: FDM, TDM within frequency channel (OFDM - orthogonal frequency division multiplexing) • “orthogonal”: minimal interference between channels • upstream: FDM, TDM similar to OFDM § each active mobile device allocated two or more 0. 5 ms time slots over 12 frequencies • scheduling algorithm not standardized – up to operator • 100’s Mbps per device possible Wireless and Mobile Networks: 7 - 46

LTE data plane protocol stack: packet core tunneling: IP Packet Data Convergence Radio Link Medium Access Physical GTP-U UDP IP link Physical base station GTP-U UDP IP link Physical S-GW § mobile datagram encapsulated using GPRS Tunneling Protocol (GTP), sent inside UDP datagram to S-GW § S-GW re-tunnels datagrams to P-GW § supporting mobility: only tunneling endpoints change when mobile user P-GW moves Wireless and Mobile Networks: 7 - 47

1 2 data 3 plane P-GW S-GW base station BS broadcasts primary synch signal every 5 ms on all frequencies § BSs from multiple carriers may be broadcasting synch signals nd synch signal on this freq. mobile finds a primary synch signal, then locates 2 § mobile then finds info broadcast by BS: channel bandwidth, configurations; BS’s cellular carrier info LTE data plane: associating with a BS 1 2 § mobile may get info from multiple base stations, multiple cellular networks 3 mobile selects which BS to associate with (e. g. , preference for home carrier) 4 more steps still needed to authenticate, establish state, set up data plane Wireless and Mobile Networks: 7 - 48

ZZZZ. . . data plane as in Wi. Fi, Bluetooth: LTE mobile may put radio to “sleep” to conserve battery: § light sleep: after 100’s msec of inactivity § wake up periodically (100’s msec) to check for downstream transmissions LTE mobiles: sleep modes § deep sleep: after 5 -10 secs of inactivity § mobile may change cells while deep sleeping – need to re-establish association Wireless and Mobile Networks: 7 - 49

Global cellular network: a network of IP networks home network HSS: Home Subscriber Server home mobile carrier network P-GW public Internet and … inter-carrier IPX … in home network P-GW roaming in visited network visited mobile carrier network … SIM card: global identify info in home network § identify & services info, while in home network and roaming all IP: § carriers interconnect with each other, and public internet at exchange points § legacy 2 G, 3 G: not all IP, handled otherwise Wireless and Mobile Networks: 7 - 50

On to 5 G! § goal: 10 x increase in peak bitrate, 10 x decrease in latency, 100 x increase in traffic capacity over 4 G § 5 G NR (new radio): § two frequency bands: FR 1 (450 MHz– 6 GHz) and FR 2 (24 GHz– 52 GHz): millimeter wave frequencies § not backwards-compatible with 4 G § MIMO: multiple directional antennae § millimeter wave frequencies: much higher data rates, but over shorter distances § pico-cells: cells diameters: 10 -100 m § massive, dense deployment of new base stations required Wireless and Mobile Networks: 7 - 51

Chapter 7 outline § Introduction Wireless Mobility § Wireless links and network characteristics § Wi. Fi: 802. 11 wireless LANs § Cellular networks: 4 G and 5 G § Mobility management: principles § Mobility management: practice • 4 G/5 G networks • Mobile IP § Mobility: impact on higher-layer protocols Link Layer: 6 -52

What is mobility? § spectrum of mobility, from the network perspective: no mobility device moves between networks, but powers down while moving high mobility device moves within same AP in one provider network device moves among APs in one provider network We’re interested in these! device moves among multiple provider networks, while maintaining ongoing connections Wireless and Mobile Networks: 7 - 53

Mobility approaches § let network (routers) handle it: • routers advertise well-known name, address (e. g. , permanent 32 -bit IP address), or number (e. g. , cell #) of visiting mobile node via usual routing table exchange • Internet routing could do this already with no changes! Routing tables indicate where each mobile located via longest prefix match! Wireless and Mobile Networks: 7 - 54

Mobility approaches § let network (routers) handle it: • routers advertise well-known name, address (e. g. , permanent 32 -bit not scalable IP address), or number (e. g. , cell #) of visiting mobile node via usual routing table exchange to billions of mobiles • Internet routing could do this already with no changes! Routing tables indicate where each mobile located via longest prefix match! § let end-systems handle it: functionality at the “edge” • indirect routing: communication from correspondent to mobile goes through home network, then forwarded to remote mobile • direct routing: correspondent gets foreign address of mobile, send directly to mobile Wireless and Mobile Networks: 7 - 55

Contacting a mobile friend: Consider friend frequently changing locations, how do you find him/her? I wonder where Alice moved to? § search all phone books? § expect her to let you know where he/she is? § call his/her parents? § Facebook! The importance of having a “home”: § a definitive source of information about you § a place where people can find out where you are Wireless and Mobile Networks: 7 - 56

Home network, visited network: 4 G/5 G home network: Home Subscriber Server home mobile carrier network P-GW public Internet and … inter-carrier IPX … in home network P-GW visited mobile carrier network … SIM card: global identify info including home roaming in network visited network § (paid) service plan with cellular provider, e. g. , Verizon, Orange § home network HSS stores identify & services info visited network: § any network other than your home network § service agreement with other networks: to provide access to visiting mobile Wireless and Mobile Networks: 7 - 57

Home network, visited network: ISP/Wi. Fi: no notion of global “home” authentication access server … … attach public Internet authentication access server … attach § credentials from ISP (e. g. , username, password) stored on device or with user § ISPs may have national, international presence § different networks: different credentials • some exceptions (e. g. , eduroam) • architectures exist (mobile IP) for 4 G-like mobility, but not used Wireless and Mobile Networks: 7 - 58

Home network, visited network: generic Home Network Visited Network e. g. , : 128. 119/16 e. g. , : 79. 129/16 Permanent IP: 128. 119. 40. 186 IMSI 78: 4 f: 43: 98: d 9: 27 Mobility manager Home Subscriber Server Home network Home gateway NAT IP: 10. 0. 0. 99 IMSI 78: 4 f: 43: 98: d 9: 27 Mobility manager Visited network gateway public or private Internet Correspondent Wireless and Mobile Networks: 7 - 59

Registration: home needs to know where you are! Home Network Visited Network e. g. , : 128. 119/16 Permanent IP: 128. 119. 40. 186 IMSI 78: 4 f: 43: 98: d 9: 27 Mobility manager Home Subscriber Server 1 2 Home network Home gateway e. g. , : 79. 129/16 NAT IP: 10. 0. 0. 99 IMSI 78: 4 f: 43: 98: d 9: 27 Visited network gateway public or private Internet Mobility manager mobile associates with visited mobility manager registers mobile’s location with home HSS end result: § visited mobility manager knows about mobile § home HSS knows location of mobile Wireless and Mobile Networks: 7 - 60

Mobility with indirect routing Home Network Visited Network e. g. , : 128. 119/16 e. g. , : 79. 129/16 Permanent IP: 128. 119. 40. 186 IMSI 78: 4 f: 43: 98: d 9: 27 Mobility manager Home Subscriber Server 2 Home network Home gateway home gateway receives datagram, forwards (tunnels) to remote gateway correspondent uses home address as datagram destination address NAT IP: 10. 0. 0. 99 IMSI Mobility manager 78: 4 f: 43: 98: d 9: 27 4 a public or private Internet 1 3 4 b Visited network visited gateway router forwards to mobile gateway visited gateway router forwards reply to correspondent via home network (4 a) or directly (4 b) Correspondent Wireless and Mobile Networks: 7 - 61

Mobility with indirect routing: comments § triangle routing: • inefficient when correspondent and mobile are in same network § mobile moves among visited networks: transparent to correspondent! • registers in new visited network • new visited network registers with home HSS • datagrams continue to be forwarded from home network to mobile in new network • on-going (e. g. , TCP) connections between correspondent and mobile can be maintained! Wireless and Mobile Networks: 7 - 62

Mobility with direct routing Home Network Visited Network e. g. , : 128. 119/16 e. g. , : 79. 129/16 Home Subscriber Server Permanent IP: 128. 119. 40. 186 IMSI 78: 4 f: 43: 98: d 9: 27 Mobility manager IMSI 4 78: 4 f: 43: 98: d 9: 27 Home gateway correspondent contacts home HSS, gets mobile’s visited network NAT IP: 10. 0. 0. 99 Visited network Mobility manager visited gateway router forwards to mobile gateway 2 public or private Internet 1 Correspondent 3 Correspondent addresses datagram to visited network address Wireless and Mobile Networks: 7 - 63

Mobility with direct routing: comments § overcomes triangle routing inefficiencies § non-transparent to correspondent: correspondent must get care-ofaddress from home agent § what if mobile changes visited network? • can be handled, but with additional complexity Wireless and Mobile Networks: 7 - 64

Chapter 7 outline § Introduction Wireless Mobility § Wireless links and network characteristics § Wi. Fi: 802. 11 wireless LANs § Cellular networks: 4 G and 5 G § Mobility management: principles § Mobility management: practice • 4 G/5 G networks • Mobile IP § Mobility: impact on higher-layer protocols Link Layer: 6 -65

Mobility in 4 G networks: major mobility tasks Home Subscriber Server Home network 1 Mobility manager MME base station 3 S-GW P-GW Internet Streaming server mobile handover: 4 P-GW 4 1 2 2 Visited network 3 base station association: § covered earlier § mobile provides IMSI – identifying itself, home network control-plane configuration: § MME, home HSS establish control-plane state - mobile is in visited network data-plane configuration: § MME configures forwarding tunnels for mobile § visited, home network establish tunnels from home P-GW to mobile § mobile device changes its point of attachment to visited network Wireless and Mobile Networks: 7 - 66

Configuring LTE control-plane elements Home Subscriber Server Home network Mobility manager MME 2 base station P-GW S-GW Visited network § Mobile communicates with local MME via BS control-plane channel § MME uses mobile’s IMSI info to contact mobile’s home HSS • retrieve authentication, encryption, network service information • home HHS knows mobile now resident in visited network § BS, mobile select parameters for BS-mobile data-plane radio channel Wireless and Mobile Networks: 7 - 67

Configuring data-plane tunnels for mobile § S-GW to BS tunnel: when mobile changes base stations, simply change endpoint IP address of tunnel § S-GW to home P-GW tunnel: implementation of indirect routing Home Subscriber Server Home network Mobility manager MME base station S-GW P-GW Internet P-GW Visited network Streaming server § tunneling via GTP (GPRS tunneling protocol): mobile’s datagram to streaming server encapsulated using GTP inside UDP, inside datagram Wireless and Mobile Networks: 7 - 68

Handover between BSs in same cellular network data path before handover P-GW data path after handover S-GW MME source BS 1 2 3 4 target BS 1 current (source) BS selects target BS, sends Handover Request message to target BS 2 target BS pre-allocates radio time slots, responds with HR ACK with info for mobile 3 source BS informs mobile of new BS § mobile can now send via new BS - handover looks complete to mobile 4 source BS stops sending datagrams to mobile, instead forwards to new BS (who forwards to mobile over radio channel) Wireless and Mobile Networks: 7 - 69

Handover between BSs in same cellular network source BS P-GW 3 1 4 2 6 S-GW 5 7 5 MME target BS 5 target BS informs MME that it is new BS for mobile § MME instructs S-GW to change tunnel endpoint to be (new) target BS 6 target BS ACKs back to source BS: handover complete, source BS can release resources 7 mobile’s datagrams now flow through new tunnel from target BS to S-GW Wireless and Mobile Networks: 7 - 70

Mobile IP § mobile IP architecture standardized ~20 years ago [RFC 5944] • long before ubiquitous smartphones, 4 G support for Internet protocols • did not see wide deployment/use • perhaps Wi. Fi for Internet, and 2 G/3 G phones for voice were “good enough” at the time § mobile IP architecture: • indirect routing to node (via home network) using tunnels • mobile IP home agent: combined roles of 4 G HSS and home P-GW • mobile IP foreign agent: combined roles of 4 G MME and S-GW • protocols for agent discovery in visited network, registration of visited location in home network via ICMP extensions Wireless and Mobile Networks: 7 - 71

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 handover loss • TCP interprets loss as congestion, will decrease congestion window unnecessarily • delay impairments for real-time traffic • bandwidth a scare resource for wireless links Wireless and Mobile Networks: 7 - 72

Chapter 7 summary Wireless § Wireless Links and network characteristics § Wi. Fi: 802. 11 wireless LANs § Cellular networks: 4 G and 5 G Mobility § Mobility management: principles § Mobility management: practice • 4 G/5 G networks • Mobile IP § Mobility: impact on higher-layer protocols Wireless and Mobile Networks: 7 - 73