1. 6: Wireless and Mobile Networks6-1 Chapter 6 outline 6.1 Introduction Wireless r 6.2 Wireless links, characteristics m CDMA r 6.3 IEEE 802.11 wireless LANs (“wi-fi”) r 6.4 Cellular Internet Access m architecture m standards (e.g., GSM) Mobility r 6.5 Principles: addressing and routing to mobile users r 6.6 Mobile IP r 6.7 Handling mobility in cellular networks r 6.8 Mobility and higher- layer protocols 6.9 Summary

2. 6: Wireless and Mobile Networks6-2 Characteristics of selected wireless link standards 384 Kbps 56 Kbps 54 Mbps 5-11 Mbps 1 Mbps 802.15 802.11b 802.11{a,g} IS-95 CDMA, GSM UMTS/WCDMA, CDMA2000.11 p-to-p link 2G 3G Indoor 10 – 30m Outdoor 50 – 200m Mid range outdoor 200m – 4Km Long range outdoor 5Km – 20Km

3. 6: Wireless and Mobile Networks6-3 Wireless Link Characteristics Differences from wired link …. m decreased signal strength (path loss) m interference from other sources m multipath propagation …. make communication across wireless link much more “difficult”

4. 6: Wireless and Mobile Networks6-4 802.11 LAN architecture r wireless host communicates with base station m base station (AP) r Basic Service Set (BSS) in infrastructure mode contains: m wireless hosts m access point (AP): base station m ad hoc mode: hosts only BSS 1 BSS 2 Internet hub, switch or router AP

5. 6: Wireless and Mobile Networks6-5 802.11: Channels, association r 802.11b: 2.4GHz-2.485GHz spectrum divided into 11 channels at different frequencies m AP admin chooses frequency for AP m interference possible: channel can be same as that chosen by neighboring AP! r host: must associate with an AP m scans channels, listening for beacon frames containing AP’s name (SSID) and MAC address m selects AP to associate with m may perform authentication [Chapter 8] m will typically run DHCP to get IP address in AP’s subnet

6. 6: Wireless and Mobile Networks6-6 IEEE 802.11: multiple access r avoid collisions: 2 + nodes transmitting at same time r 802.11: CSMA - sense before transmitting m don’t collide with ongoing transmission by other node r 802.11: no collision detection! m difficult to receive (sense collisions) when transmitting due to weak received signals (fading) m can’t sense all collisions in any case: hidden terminal, fading m goal: avoid collisions: CSMA/C(ollision)A(voidance) A B C A B C A’s signal strength space C’s signal strength

7. 6: Wireless and Mobile Networks6-7 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 time timer counts down while channel idle transmit when timer expires if no ACK, increase random backoff interval, repeat 2 802.11 receiver - if frame received OK return ACK after SIFS (ACK needed due to hidden terminal problem) sender receiver DIFS data SIFS ACK

8. 6: Wireless and Mobile Networks6-8 Avoiding collisions (more) idea: allow sender to “reserve” channel rather than random access of data frames: avoid collisions of long data frames r sender first transmits small RTS packets to BS using CSMA m RTS may still collide with each other r BS broadcasts CTS in response to RTS r RTS heard by all nodes m sender transmits data frame m other stations defer transmissions Avoid data frame collisions completely using small reservation packets!

9. 6: Wireless and Mobile Networks6-9 Collision Avoidance: RTS-CTS exchange AP A B time RTS(A) RTS(B) RTS(A) CTS(A) DATA (A) ACK(A) reservation collision defer

10. 6: Wireless and Mobile Networks6-10 hub or switch AP 2 AP 1 H1 BBS 2 BBS 1 802.11: mobility within same subnet router r H1 remains in same IP subnet: IP address can remain same r switch: which AP is associated with H1? m self-learning (Ch. 5): switch will see frame from H1 and “remember” which switch port can be used to reach H1

11. 6: Wireless and Mobile Networks6-11 M radius of coverage S S S P P P P M S Master device Slave device Parked device (inactive) P 802.15: personal area network r less than 10 m diameter r replacement for cables (mouse, keyboard, headphones) r ad hoc: no infrastructure r master/slaves: m slaves request permission to send (to master) m master grants requests r 802.15: evolved from Bluetooth specification m 2.4-2.5 GHz radio band m up to 721 kbps

12. 6: Wireless and Mobile Networks6-12 Mobile Switching Center Public telephone network, and Internet Mobile Switching Center Components of cellular network architecture  connects cells to wide area net  manages call setup (more later!)  handles mobility (more later!) MSC  covers geographical region  base station (BS) analogous to 802.11 AP  mobile users attach to network through BS  air-interface: physical and link layer protocol between mobile and BS cell wired network

13. 6: Wireless and Mobile Networks6-13 Cellular networks: the first hop Two techniques for sharing mobile-to-BS radio spectrum r combined FDMA/TDMA: divide spectrum in frequency channels, divide each channel into time slots r CDMA: code division multiple access frequency bands time slots

14. 6: Wireless and Mobile Networks6-14 Cellular standards: brief survey 2G systems: voice channels r IS-136 TDMA: combined FDMA/TDMA (north America) r GSM (global system for mobile communications): combined FDMA/TDMA m most widely deployed r IS-95 CDMA: code division multiple access IS-136 GSM IS-95 GPRS EDGE CDMA-2000 UMTS TDMA/FDMA

15. 6: Wireless and Mobile Networks6-15 Cellular standards: brief survey 2.5 G systems: voice and data channels r for those who can’t wait for 3G service: 2G extensions r general packet radio service (GPRS) m evolved from GSM m data sent on multiple channels (if available) r enhanced data rates for global evolution (EDGE) m also evolved from GSM, using enhanced modulation m Date rates up to 384K r CDMA-2000 (phase 1) m data rates up to 144K m evolved from IS-95

16. 6: Wireless and Mobile Networks6-16 Cellular standards: brief survey 3G systems: voice/data r Universal Mobile Telecommunications Service (UMTS) m GSM next step, but using CDMA r CDMA-2000 ….. more (and more interesting) cellular topics due to mobility (stay tuned for details)

17. 6: Wireless and Mobile Networks6-17 What is mobility? r spectrum of mobility, from the network perspective: no mobility high mobility mobile wireless user, using same access point mobile user, passing through multiple access point while maintaining ongoing connections ( like cell phone) mobile user, connecting/ disconnecting from network using DHCP.

18. 6: Wireless and Mobile Networks6-18 Mobility: Vocabulary home network: permanent “home” of mobile (e.g., 128.119.40/24) Permanent address: address in home network, can always be used to reach mobile e.g., 128.119.40.186 home agent: entity that will perform mobility functions on behalf of mobile, when mobile is remote wide area network correspondent

19. 6: Wireless and Mobile Networks6-19 Mobility: more vocabulary Care-of-address: address in visited network. (e.g., 79,129.13.2) wide area network visited network: network in which mobile currently resides (e.g., 79.129.13/24) Permanent address: remains constant ( e.g., 128.119.40.186) foreign agent: entity in visited network that performs mobility functions on behalf of mobile. correspondent: wants to communicate with mobile

20. 6: Wireless and Mobile Networks6-20 Mobility: approaches r Let routing handle it: routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange. m routing tables indicate where each mobile located m no changes to end-systems r Let end-systems handle it: m indirect routing: communication from correspondent to mobile goes through home agent, then forwarded to remote m direct routing: correspondent gets foreign address of mobile, sends directly to mobile

21. 6: Wireless and Mobile Networks6-21 Mobility: approaches r Let routing handle it: routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange. m routing tables indicate where each mobile located m no changes to end-systems r let end-systems handle it: m indirect routing: communication from correspondent to mobile goes through home agent, then forwarded to remote m direct routing: correspondent gets foreign address of mobile, sends directly to mobile not scalable to millions of mobiles

22. 6: Wireless and Mobile Networks6-22 Mobility: registration End result: r Foreign agent knows about mobile r Home agent knows location of mobile wide area network home network visited network 1 mobile contacts foreign agent on entering visited network 2 foreign agent contacts home agent: “this mobile is resident in my network”

23. 6: Wireless and Mobile Networks6-23 Mobility via Indirect Routing wide area network home network visited network 3 2 4 1 correspondent addresses packets using home address of mobile home agent intercepts packets, forwards to foreign agent foreign agent receives packets, forwards to mobile mobile replies directly to correspondent

24. 6: Wireless and Mobile Networks6-24 Indirect Routing: comments r Mobile uses two addresses: m permanent address: used by correspondent (hence mobile location is transparent to correspondent) m care-of-address: used by home agent to forward datagrams to mobile r foreign agent functions may be done by mobile itself r triangle routing: correspondent-home-network- mobile m inefficient when correspondent, mobile are in same network

25. 6: Wireless and Mobile Networks6-25 Indirect Routing: moving between networks r suppose mobile user moves to another network m registers with new foreign agent m new foreign agent registers with home agent m home agent update care-of-address for mobile m packets continue to be forwarded to mobile (but with new care-of-address) r mobility, changing foreign networks transparent: on going connections can be maintained!

26. 6: Wireless and Mobile Networks6-26 Mobility via Direct Routing wide area network home network visited network 4 2 4 1 correspondent requests, receives foreign address of mobile correspondent forwards to foreign agent foreign agent receives packets, forwards to mobile mobile replies directly to correspondent 3

27. 6: Wireless and Mobile Networks6-27 Mobility via Direct Routing: comments r overcome triangle routing problem r non-transparent to correspondent: correspondent must get care-of-address from home agent m what if mobile changes visited network?

28. 6: Wireless and Mobile Networks6-28 wide area network 1 foreign net visited at session start anchor foreign agent 2 4 new foreign agent 3 5 correspondent agent correspondent new foreign network Accommodating mobility with direct routing r anchor foreign agent: FA in first visited network r data always routed first to anchor FA r when mobile moves: new FA arranges to have data forwarded from old FA (chaining)