1. CPSC 441: Wireless1 Instructor: Anirban Mahanti Office: ICT 745 Email: mahanti@cpsc.ucalgary.ca Class Location: ICT 121 Lectures: MWF 12:00 – 12:50 hours Notes derived from “ Computer Networking: A Top Down Approach Featuring the Internet”, 2005, 3 rd edition, Jim Kurose, Keith Ross, Addison-Wesley. Slides are adapted from the companion web site of the book, as modified by Anirban Mahanti (and Carey Williamson). Wireless and Mobile Networks

2. CPSC 441: Wireless2 Outline r Introduction r Standards and Link Characteristics r IEEE 802.11 Wireless LANS r Mobility r Wireless/Mobility Performance Issues r Summary

3. CPSC 441: Wireless3 What is Wireless Networking? r The use of infra-red (IR) or radio frequency (RF) signals to share information and resources between devices r Promises anytime, anywhere connectivity m laptops, palmtops, PDAs, Internet-enabled phone promise anytime untethered Internet access r Two important (but different) challenges m communication over wireless link m handling mobile user who changes point of attachment to network r Buzz words! m Mobile Internet, Pervasive Computing, Nomadic Computing, M-Commerce, Ubiquitous Computing …

4. CPSC 441: Wireless4 Wireless Networking Technologies r Mobile devices – laptop, PDA, cellular phone, wearable computer, … r Operating modes m Infrastructure mode (Access Point) m Ad hoc mode r Access technology m Bluetooth (1 Mbps, up to 3 meters) m IEEE 802.11 (up to 55 Mbps, 20 – 100 meters)

5. CPSC 441: Wireless5 Infrastructure Mode network infrastructure infrastructure mode r base station connects mobiles into wired network r handoff: mobile changes base station providing connection into wired network

6. CPSC 441: Wireless6 Ad hoc Mode 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

7. CPSC 441: Wireless7 Outline r Introduction r Standards and Link Characteristics r IEEE 802.11 Wireless LANS r Mobility r Wireless/Mobility Performance Issues r Summary

8. CPSC 441: Wireless8 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

9. CPSC 441: Wireless9 Two Popular 2.4 GHz Standards: r IEEE 802.11 m Fast (11b) m High Power m Long range m Single-purpose m Ethernet replacement m Easily Available Apple Airport, iBook, G4 Cisco Aironet 350 r Bluetooth m Slow m Low Power m Short range m Flexible m Cable replacement

10. CPSC 441: Wireless10 Wireless Link Characteristics Differences from wired link …. m Decreasing 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., phone); devices (motors) interfere as well m Multi-path 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”

11. CPSC 441: Wireless11 Wireless Network Characteristics Multiple wireless senders and receivers create additional problems (beyond multiple access): 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 fading: r B, A hear each other r B, C hear each other r A, C can not hear each other interfering at B

12. CPSC 441: Wireless12 Outline r Introduction r Standards and Link Characteristics r IEEE 802.11 Wireless LANS r Mobility r Wireless/Mobility Performance Issues r Summary

13. CPSC 441: Wireless13 IEEE 802.11 Organization Tree:

14. CPSC 441: Wireless14 IEEE 802.11 Wireless LAN r 802.11b m 2.4-5 GHz unlicensed radio spectrum m up to 11 Mbps m direct sequence spread spectrum (DSSS) in physical layer all hosts use same chipping code m widely deployed, using base stations r 802.11a m 5-6 GHz range m up to 54 Mbps r 802.11g m 2.4-5 GHz range m up to 54 Mbps r All use CSMA/CA for multiple access r All have base-station and ad-hoc network versions

15. CPSC 441: Wireless15 802.11 LAN architecture r wireless host communicates with base station m base station = access point (AP) r Basic Service Set (BSS) (aka “cell”) 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

16. CPSC 441: Wireless16 Wireless Cells r 802.11 has 11 channels r Channels 1, 6, and 11 are non-overlapping r Each AP coverage area is called a “cell” r Wireless nodes can roam between cells r Q. Suppose an administrator setups three 802.11b APs at the same physical location. What is the maximum possible aggregate throughput of this WLAN? AP Channel 1 Channel 6 Channel 1 Channel 11 Channel 6 Channel 1

17. CPSC 441: Wireless17 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

18. CPSC 441: Wireless18 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 3 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

19. CPSC 441: Wireless19 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 request-to-send (RTS) packets to base station using CSMA m RTSs may still collide with each other (but they’re short) r BS broadcasts clear-to-send 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!

20. CPSC 441: Wireless20 Collision Avoidance: RTS-CTS exchange AP A B time RTS(A) RTS(B) RTS(A) CTS(A) DATA (A) ACK(A) reservation collision defer

21. CPSC 441: Wireless21 frame control duration address 1 address 2 address 4 address 3 payloadCRC 226662 6 0 - 2312 4 seq control 802.11 frame: addressing Address 2: MAC address of wireless host or AP transmitting this frame Address 1: MAC address of wireless host or AP to receive this frame Address 3: MAC address of router interface to which AP is attached Address 3: used only in ad hoc mode

22. CPSC 441: Wireless22 Internet router AP H1 R1 AP MAC addr H1 MAC addr R1 MAC addr address 1 address 2 address 3 802.11 frame R1 MAC addr AP MAC addr dest. address source address 802.3 frame 802.11 frame: addressing

23. CPSC 441: Wireless23 frame control duration address 1 address 2 address 4 address 3 payloadCRC 226662 6 0 - 2312 4 seq control Type From AP Subtype To AP More frag WEP More data Power mgt RetryRsvd Protocol version 2 2411111111 802.11 frame: more duration of reserved transmission time (RTS/CTS) frame seq # (for reliable ARQ) frame type (RTS, CTS, ACK, data)

24. CPSC 441: Wireless24 Outline r Introduction r Standards and Link Characteristics r IEEE 802.11 Wireless LANS r Mobility r Wireless/Mobility Performance Issues r Summary

25. CPSC 441: Wireless25 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.

26. CPSC 441: Wireless26 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

27. CPSC 441: Wireless27 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

28. CPSC 441: Wireless28 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) home agent: entity in visited network that performs mobility functions on behalf of mobile. correspondent: wants to communicate with mobile

29. CPSC 441: Wireless29 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?

30. CPSC 441: Wireless30 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

31. CPSC 441: Wireless31 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

32. CPSC 441: Wireless32 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”

33. CPSC 441: Wireless33 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

34. CPSC 441: Wireless34 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

35. CPSC 441: Wireless35 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!

36. CPSC 441: Wireless36 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

37. CPSC 441: Wireless37 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?

38. CPSC 441: Wireless38 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)

39. CPSC 441: Wireless39 Mobile IP r RFC 3220 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

40. CPSC 441: Wireless40 Outline r Introduction r Standards and Link Characteristics r IEEE 802.11 Wireless LANS r Mobility r Wireless/Mobility Performance Issues r Summary

41. CPSC 441: Wireless41 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

42. CPSC 441: Wireless42 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 Mobile IP r impact on higher-layer protocols