6-1 Chapter 6 Wireless and Mobile Networks All material copyright J.F Kurose and K.W. Ross, All Rights Reserved

6: Wireless and Mobile Networks 6-2 Chapter 6 outline 6.1 Introduction Wireless r 6.2 Wireless links, characteristics m CDMA r 6.3 IEEE 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

6: Wireless and Mobile Networks 6-3 Chapter 6: Wireless and Mobile Networks Background: r # wireless (mobile) phone subscribers now exceeds # wired phone subscribers! m “Mobile subscriptions outnumber fixed lines 5:1” r computer nets: laptops, palmtops, PDAs, Internet-enabled phone promise anytime Internet access r two important (but different) challenges m wireless: communication over wireless link m mobility: handling the mobile user who changes point of attachment to network

r The Wireless LAN is usually an extension of the Ethernet LAN. Wireless Networks

Comparing a WLAN to a LAN Wireless Access Points (AP) instead of a switch. Wireless NICs tend to reduce battery life. CSMA/CA (Avoidance) instead of CSMA/CD CSMA/CA (Avoidance) instead of CSMA/CD Different Frame Format Privacy Issues

Comparing a WLAN to a LAN Network Architecture Standards Physical Media

6: Wireless and Mobile Networks 6-7 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

6: Wireless and Mobile Networks 6-8 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, access points

Base Stations: 6: Wireless and Mobile Networks 6-9

6: Wireless and Mobile Networks 6-10 Elements of a wireless network network infrastructure wireless link r typically used to connect mobile(s) to base station r also used as backbone link r various data rates, transmission distance

6: Wireless and Mobile Networks 6-11 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

6: Wireless and Mobile Networks 6-12 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

6: Wireless and Mobile Networks 6-13 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 to reach other a given wireless node MANET, VANET

6: Wireless and Mobile Networks 6-14 Wireless Link Characteristics r decreased signal strength: radio signal attenuates as it propagates through matter (path loss) r 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 r multipath propagation: radio signal reflects off objects ground, arriving ad destination at slightly different times …. make communication across (even a point to point) wireless link much more “difficult”

6: Wireless and Mobile Networks 6-15 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 attenuation: r B, A hear each other r B, C hear each other r A, C can not hear each other interfering at B

6: Wireless and Mobile Networks 6-16 Chapter 6 outline 6.1 Introduction Wireless r 6.2 Wireless links, characteristics m CDMA r 6.3 IEEE 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

r An IEEE standard defines m how radio frequency (RF) in the unlicensed industrial, scientific, and medical (ISM) frequency bands is used for the Physical layer and the MAC sub-layer of wireless links. m Typically, the choice of which standard to use is based on data rate. Wireless LAN Standards

6: Wireless and Mobile Networks 6-18 Wireless Link Standards Indoor 10-30m Outdoor m Mid-range outdoor 200m – 4 Km Long-range outdoor 5Km – 20 Km IS-95, CDMA, GSM 2G UMTS/WCDMA, CDMA2000 3G b a,g UMTS/WCDMA-HSPDA, CDMA2000-1xEVDO 3G cellular enhanced (WiMAX) a,g point-to-point n Data rate (Mbps) data

Wireless Standards

6: Wireless and Mobile Networks 6-20 IEEE b r b m GHz unlicensed spectrum m up to 11 Mbps m direct sequence spread spectrum (DSSS) in physical layer r Pros :lowest cost; signal range is good and not easily obstructed r Cons : slowest maximum speed; home appliances may interfere

6: Wireless and Mobile Networks 6-21 IEEE a r a m 5-6 GHz range m up to 54 Mbps r Pros :fast maximum speed; regulated frequencies prevent signal interference r Cons: highest cost; high frequency signal that is more easily obstructed

6: Wireless and Mobile Networks 6-22 r g r GHz range r up to 54 Mbps r Pros: fast maximum speed; signal range is good and not easily obstructed r Cons: costs more than b; appliances may interfere on the unregulated signal frequency IEEE g r all use CSMA/CA for multiple access r all have base-station and ad-hoc network versions

6: Wireless and Mobile Networks 6-23 IEEE n r n: m GHz range m up to 200 Mbps m utilizing multiple wireless signals and antennas (called MIMO technology) instead of one. r Pros : fastest maximum speed and best signal range r Cons :- standard is not yet finalized; costs more than g; the use of multiple signals may greatly interfere with nearby b/g based networks.

6: Wireless and Mobile Networks 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

6: Wireless and Mobile Networks : Channels, association r Each AP has a identifier called SSID(Service Set Identifier). r A 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 m will typically run DHCP to get IP address in AP’s subnet

6: Wireless and Mobile Networks : Channels, association r b: 2.4GHz-2.485GHz spectrum divided into 11 partially overlapping channels at different frequencies. m AP admin chooses frequency for AP m Channels chosen must be non overlapping. (Separated by 4 or more channels) m So out of 85 MHz band, 1,6,11 are non overlapping. m interference possible: channel can be same as that chosen by neighboring AP!

6: Wireless and Mobile Networks : Channels

6: Wireless and Mobile Networks : Passive scanning AP 2 AP 1 H1 BBS 2 BBS Passive Scanning:  Beacon frames sent from APs  Beacon contains SSID and MAC of AP.  H1 chooses AP, with highest signal strength.  Association Request frame sent: from H1 to selected AP  Association Response frame sent: to H1 from selected AP

6: Wireless and Mobile Networks : Active scanning AP 2 AP 1 H1 BBS 2 BBS Active Scanning :  Probe Request frame broadcast from H1  Probes response frame sent from APs  Association Request frame sent: from H1 to selected AP  Association Response frame sent: to H1 from selected AP

Association: r Once associated with AP, H1 will acquire IP address of the subnet that the AP belongs to. r Before association authentication may be required with the AP: m Based on host’s MAC address m Based on Usernames and Passwords. 6: Wireless and Mobile Networks 6-30

6: Wireless and Mobile Networks 6-31 IEEE : multiple access r avoid collisions: 2 + nodes transmitting at same time r : CSMA - sense before transmitting r : 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 r goal: avoid collisions: CSMA/C(ollision)A(voidance)

6: Wireless and Mobile Networks 6-32 IEEE MAC Protocol: CSMA/CA sender 1 if sense channel idle for DIFS then m transmit entire frame 2 if sense channel busy then m start random backoff time m timer counts down while channel idle m transmit when timer expires m if no ACK, increase random backoff interval, repeat receiver 1. if frame received OK m return ACK after SIFS (ACK needed due to hidden terminal problem) sender receiver DIFS data SIFS ACK

6: Wireless and Mobile Networks 6-33 Avoiding collisions (more) idea: allow sender to “reserve” channel rather than random access of data frames. r sender first transmits small request-to-send (RTS) packets to BS using CSMA r BS broadcasts clear-to-send CTS in response to RTS r CTS heard by all nodes m sender transmits data frame m other stations defer transmissions avoid data frame collisions completely using small reservation packets!

6: Wireless and Mobile Networks 6-34 Collision Avoidance: RTS-CTS exchange AP A B time RTS(A) RTS(B) RTS(A) CTS(A) DATA (A) ACK(A) reservation collision defer

RTS/CTS Exchange r RTS and CTS are short, so collisions involving an RTS or CTS are short. r RTS/CTS also introduces delay and consumes channel resources. r So RTS/CTS only used if long DATA frame is sent. 6: Wireless and Mobile Networks 6-35

6: Wireless and Mobile Networks 6-36 frame control duration address 1 address 2 address 4 address 3 payloadCRC seq control 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 4: used only in ad hoc mode

6: Wireless and Mobile Networks 6-37 Internet router AP H1 R1 AP MAC addr H1 MAC addr R1 MAC addr address 1 address 2 address frame R1 MAC addr H1 MAC addr dest. address source address frame frame: addressing

6: Wireless and Mobile Networks 6-38 frame control duration address 1 address 2 address 4 address 3 payloadCRC seq control frame: more duration of reserved transmission time (RTS/CTS) frame seq #

6: Wireless and Mobile Networks 6-39 frame control duration address 1 address 2 address 4 address 3 payloadCRC seq control Type From AP Subtype To AP More frag WEP More data Power mgt RetryRsvd Protocol version frame: more frame type (RTS, CTS, ACK, data)

6: Wireless and Mobile Networks 6-40 hub or switch AP 2 AP 1 H1 BBS 2 BBS : mobility within same subnet router r 2 BSSs is interconnected by a switch r As H1 moves, detects higher beacon signal of AP2 and associates with AP2. r H1 remains in same IP subnet: IP address can remain same. r No problem with TCP connections.

6: Wireless and Mobile Networks 6-41 hub or switch AP 2 AP 1 H1 BBS 2 BBS : mobility within same subnet router r Switch: which AP is associated with H 1? Which port? r Solution: m AP2 sends a broadcast frame with H1 source address. m Switch updates table. m Or use different inter AP Protocols.

6: Wireless and Mobile Networks 6-42 Chapter 6 outline 6.1 Introduction Wireless r 6.2 Wireless links, characteristics m CDMA r 6.3 IEEE 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

6: Wireless and Mobile Networks 6-43 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.

6: Wireless and Mobile Networks 6-44 Mobility: Vocabulary home network: permanent “home” of mobile (e.g., /24) Permanent address: address in home network, can always be used to reach mobile e.g., home agent: entity that will perform mobility functions on behalf of mobile, when mobile is remote wide area network correspondent

6: Wireless and Mobile Networks 6-45 Mobility: more vocabulary Care-of-address: address in visited network. (e.g., 79, ) wide area network visited network: network in which mobile currently resides (e.g., /24) Permanent address: remains constant ( e.g., ) foreign agent: entity in visited network that performs mobility functions on behalf of mobile. correspondent: wants to communicate with mobile

6: Wireless and Mobile Networks 6-46 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?

6: Wireless and Mobile Networks 6-47 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

6: Wireless and Mobile Networks 6-48 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

6: Wireless and Mobile Networks 6-49 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”

6: Wireless and Mobile Networks 6-50 Mobility via Indirect Routing wide area network home network visited network 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

6: Wireless and Mobile Networks 6-51 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

6: Wireless and Mobile Networks 6-52 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!

6: Wireless and Mobile Networks 6-53 Mobility via Direct Routing wide area network home network visited network 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

6: Wireless and Mobile Networks 6-54 Mobility via Direct Routing: comments r overcome triangle routing problem but increases complexity. r non-transparent to correspondent: correspondent must get care-of-address from home agent m what if mobile changes visited network?

6: Wireless and Mobile Networks 6-55 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)

6: Wireless and Mobile Networks 6-56 Chapter 6 outline 6.1 Introduction Wireless r 6.2 Wireless links, characteristics m CDMA r 6.3 IEEE 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

6: Wireless and Mobile Networks 6-57 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

6: Wireless and Mobile Networks 6-58 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

6: Wireless and Mobile Networks 6-59 Mobile IP: indirect routing Permanent address: Care-of address: dest: packet sent by correspondent dest: dest: packet sent by home agent to foreign agent: a packet within a packet dest: foreign-agent-to-mobile packet

6: Wireless and Mobile Networks 6-60 Mobile IP: registration example

6: Wireless and Mobile Networks 6-61 Chapter 6 Summary Wireless r wireless links: m capacity, distance m channel impairments m CDMA r IEEE (“wi-fi”) m CSMA/CA reflects wireless channel characteristics r cellular access m architecture m standards (e.g., GSM, CDMA-2000, UMTS) Mobility r principles: addressing, routing to mobile users m home, visited networks m direct, indirect routing m care-of-addresses r case studies m mobile IP m mobility in GSM r impact on higher-layer protocols