1. 6-1 Chapter 6 outline Introduction Wireless r Wireless links, characteristics r IEEE 802.11 wireless LANs (“wi-fi”) Mobility r Principles: addressing and routing to mobile users r Mobility and higher- layer protocols Summary

2. 6-2 Elements of a wireless network network infrastructure wireless hosts r laptop, PDA, IP phone r run applications r may be stationary (non-mobile) or mobile m wireless does not always mean mobility

3. 6-3 Elements of a wireless network network infrastructure base station r typically connected to wired network r relay - responsible for sending packets between wired network and wireless host(s) in its “area” m e.g., cell towers, 802.11 access points

4. 6-4 Elements of a wireless network network infrastructure wireless link r typically used to connect mobiles to base station r can also be used as backbone link r multiple access protocol for link access r various data rates, transmission distance

5. 6-5 Characteristics of selected wireless link standards Indoor 10-30m Outdoor 50-200m Mid-range outdoor 200m – 4 Km Long-range outdoor 5Km – 20 Km.056.384 1 4 5-11 54 IS-95, CDMA, GSM 2G UMTS/WCDMA, CDMA2000 3G 802.15 802.11b 802.11a,g UMTS/WCDMA-HSPDA, CDMA2000-1xEVDO 3G cellular enhanced 802.16 (WiMAX) 802.11a,g point-to-point 200 802.11n Data rate (Mbps) data

6. 6-6 Elements of a wireless network network infrastructure infrastructure mode r base station connects mobiles into wired network r handoff: mobile changes base station providing connection into wired network

7. 6-7 Elements of a wireless network ad hoc mode r no base stations r nodes can only transmit to other nodes within link coverage r nodes organize themselves into a network: route among themselves

8. 6-8 Wireless network taxonomy single hop multiple hops infrastructure (e.g., APs) no infrastructure host connects to base station (WiFi, WiMAX, cellular) which connects to larger Internet no base station, no connection to larger Internet (Bluetooth, ad hoc nets) host may have to relay through several wireless nodes to connect to larger Internet: mesh net no base station, no connection to larger Internet. May have to relay through other wireless nodes to reach some node: MANET, VANET

9. 6-9 Wireless Link Characteristics (1) Differences from wired link …. m decreased signal strength: radio signal attenuates as it propagates through matter (path loss) m interference from other sources: standardized wireless network frequencies (e.g., 2.4 GHz) shared by other devices (e.g., cordless phone); devices (motors) interfere as well m multipath propagation: radio signal reflects off objects, reaching destination at slightly different times …. make communication across a wireless link much more “difficult”

10. 6-10 Wireless network characteristics Multiple wireless senders and receivers create additional problems (carrier sensing is unreliable): A B C Hidden terminal problem r B, A hear each other r B, C hear each other r A, C can not hear each other means A, C unaware of their interference at B A B C A’s signal strength space C’s signal strength Signal attenuation: r B, A hear each other r B, C hear each other r A, C can not hear each other interfering at B

11. 6-11 Chapter 6 outline Introduction Wireless r Wireless links, characteristics r IEEE 802.11 wireless LANs (“wi-fi”) Mobility r Principles: addressing and routing to mobile users r Mobility and higher- layer protocols Summary

12. 6-12 802.11 LAN architecture Basic Service Set (BSS) aka “cell” r in infrastructure mode contains: m wireless hosts, and m access point (AP): base station m adjacent APs should use different channels r in ad hoc mode, hosts only BSS 1 BSS 2 Internet hub, switch or router AP

13. 6-13 802.11: channels, association r frequency band divided into 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 [more in Chapter 8] m will typically run DHCP to get IP address in AP’s subnet

14. 6-14 802.11: passive/active scanning AP 2 AP 1 H1 BBS 2 BBS 1 1 2 2 3 4 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: selected AP to H1 AP 2 AP 1 H1 BBS 2 BBS 1 1 2 3 1 Passive Scanning: (1)beacon frames sent from APs (2)association Request frame sent: H1 to selected AP (3)association Response frame sent: selected AP to H1

15. 6-15 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

16. 6-16 Collision Avoidance: RTS-CTS exchange AP A B time RTS(A) RTS(B) RTS(A) CTS(A) DATA (A) ACK(A) reservation collision defer

17. 6-17 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

18. 6-18 802.16: WiMAX r like 802.11 & cellular: base station model m transmissions to/from base station by hosts with omnidirectional antenna m base station-to-base station backhaul with point-to-point antenna r unlike 802.11: m range ~ 6 miles (“city rather than coffee shop”), highway speed m ~14 Mbps point-to-multipoint point-to-point

19. 6-19 Chapter 6: Wireless and Mobile Networks Two important (but different) challenges r wireless: communication over wireless link r mobility: handling the mobile user who changes point of attachment to network

20. 6-20 Chapter 6 outline Introduction Wireless r Wireless links, characteristics r IEEE 802.11 wireless LANs (“wi-fi”) Mobility r Principles: addressing and routing to mobile users r Mobility and higher- layer protocols Summary

21. 6-21 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.

22. 6-22 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

23. 6-23 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

24. 6-24 How do you contact a mobile friend: r search all phone books? r call her parents? r expect her to let you know where he/she is? I wonder where Alice moved to? Consider friend frequently changing addresses, how do you find her?

25. 6-25 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

26. 6-26 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

27. 6-27 Mobility: registration End result: r Foreign agent knows about mobile r Home agent knows location of mobile wide area network home network visited network 1 mobile contacts foreign agent on entering visited network 2 foreign agent contacts home agent home: “this mobile is resident in my network”

28. 6-28 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

29. 6-29 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

30. 6-30 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!

31. 6-31 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

32. 6-32 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?

33. 6-33 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)

34. 6-34 Mobile IP r RFC 3344 r has many features we’ve seen: m home agents, foreign agents, foreign-agent registration, care-of-addresses, encapsulation (packet-within-a-packet) r three components to standard: m indirect routing of datagrams m agent discovery m registration with home agent

35. 6-35 Mobile IP: indirect routing Permanent address: 128.119.40.186 Care-of address: 79.129.13.2 dest: 128.119.40.186 packet sent by correspondent dest: 79.129.13.2 dest: 128.119.40.186 packet sent by home agent to foreign agent: a packet within a packet dest: 128.119.40.186 foreign-agent-to-mobile packet

36. 6-36 Mobile IP: agent discovery r agent advertisement: foreign/home agents advertise service by broadcasting ICMP messages (typefield = 9) R bit: registration required H,F bits: home and/or foreign agent

37. 6-37 Mobile IP: registration example

38. 6-38 Wireless, mobility: impact on higher layer protocols r logically, impact should be minimal … m best effort service model remains unchanged m TCP and UDP can (and do) run over wireless, mobile r … but performance-wise: m packet loss/delay due to bit-errors (discarded packets, delays for link-layer retransmissions), and handoff m TCP interprets loss as congestion, will decrease congestion window un-necessarily m delay impairments for real-time traffic m limited bandwidth of wireless links

39. 6-39 Chapter 6 Summary Wireless r wireless links: m capacity, distance m channel impairments m CDMA r IEEE 802.11 (“wi-fi”) m CSMA/CA reflects wireless channel characteristics Mobility r principles: addressing, routing to mobile users m home, visited networks m direct, indirect routing m care-of-addresses r impact on higher-layer protocols