Wireless and Mobile Networks Raj Jain Washington University in Saint Louis Saint Louis, MO 63130 [email protected] Audio/Video recordings of this lecture are available on-line at: http://www.cse.wustl.edu/~jain/cse473-16/ Washington University in St. Louis http://www.cse.wustl.edu/~jain/cse473-16/ ©2016 Raj Jain 7-1 Overview 1. Wireless Link Characteristics 2. Wireless LANs and PANs 3. Cellular Networks 4. Mobility Management 5. Impact on Higher Layers Note: This class lecture is based on Chapter 7 of the textbook (Kurose and Ross) and the figures provided by the authors. Washington University in St. Louis http://www.cse.wustl.edu/~jain/cse473-16/ ©2016 Raj Jain 7-2 Wireless Link Overview Characteristics q Mobile vs. Wireless q Wireless Networking Challenges q Peer-to-Peer or Base Stations? q Code Division Multiple Access (CDMA) q Direct-Sequence Spread Spectrum q Frequency Hopping Spread Spectrum Washington University in St. Louis http://www.cse.wustl.edu/~jain/cse473-16/ ©2016 Raj Jain 7-3 Mobile vs Wireless Mobile Wireless q Mobile vs Stationary q Wireless vs Wired q Wireless ⇒ media sharing issues q Mobile ⇒ routing, addressing issues Washington University in St. Louis http://www.cse.wustl.edu/~jain/cse473-16/ ©2016 Raj Jain 7-4 Wireless Networking Challenges 1. Propagation Issues: Shadows, Multipath 2. Interference ⇒ High loss rate, Variable Channel ⇒ Retransmissions and Cross-layer optimizations 3. Transmitters and receivers moving at high speed ⇒ Doppler Shift 4. Low power transmission ⇒ Limited reach 100mW in WiFi base station vs. 100 kW TV tower 5. License-Exempt spectrum ⇒ Media Access Control 6. Limited spectrum ⇒ Limited data rate Original WiFi (1997) was 2 Mbps. New standards allow up to 200 Mbps 7. No physical boundary ⇒ Security 8. Mobility ⇒ Seamless handover Washington University in St. Louis http://www.cse.wustl.edu/~jain/cse473-16/ ©2016 Raj Jain 7-5 Peer-to-Peer or Base Stations? q Ad-hoc (Autonomous) Group: q Two stations can communicate q All stations have the same logic q No infrastructure, Suitable for small area q Infrastructure Based: Access points (base units) q Stations can be simpler than bases. q Base provide connection for off-network traffic q Base provides location tracking, directory, authentication ⇒ Scalable to large networks q IEEE 802.11 provides both. Washington University in St. Louis http://www.cse.wustl.edu/~jain/cse473-16/ ©2016 Raj Jain 7-6 Characteristics of Selected Wireless Link Standards 200 802.11n 802.11a,g 54 802.11a,g point-to-point data 5-11 802.11b 802.16 (WiMAX) 4 UMTS/WCDMA-HSPDA, CDMA2000-1xEVDO 3G cellular enhanced 1 802.15 Data rate (Mbps) rate Data .384 UMTS/WCDMA, CDMA2000 3G .056 IS-95, CDMA, GSM 2G Indoor Outdoor Mid-range Long-range 10-30m 50-200m outdoor outdoor 200m – 4 Km 5Km – 20 Km Washington University in St. Louis http://www.cse.wustl.edu/~jain/cse473-16/ ©2016 Raj Jain 7-7 Wireless Network Taxonomy Single hop Multiple hops Host connects to Host may have to Infrastructure base station (WiFi, relay through several (Access Points, WiMAX, cellular) wireless nodes to connect to larger Towers) which connects to larger Internet Internet: Mesh net No Relay to reach other a given No base station Infrastructure wireless node. Mobile Ad- (Bluetooth, hoc Network (MANET), ad hoc nets) Vehicular Ad-hoc Network (VANET) Washington University in St. Louis http://www.cse.wustl.edu/~jain/cse473-16/ ©2016 Raj Jain 7-8 Wireless and Mobile Networks 7-8 Hidden Node Problem C B A B C A q B and A can hear each other B and C can hear each other A and C cannot hear each other ⇒ C is hidden for A and vice versa q C may start transmitting while A is also transmitting A and C can't detect collision. q Only the receiver can help avoid collisions Washington University in St. Louis http://www.cse.wustl.edu/~jain/cse473-16/ ©2016 Raj Jain 7-9 Direct-Sequence Spread Spectrum CDMA 0 1 Data 01 0 0 1 0 1 1 0 1 1 0 1 1 0 1 0 0 1 0 Amplitude 5µs Time q Spreading factor = Code bits/data bit, 10-100 commercial (Min 10 by FCC), 10,000 for military q Signal bandwidth >10 × data bandwidth q Code sequence synchronization q Correlation between codes ⇒Interference⇒Orthogonal Washington University in St. Louis http://www.cse.wustl.edu/~jain/cse473-16/ ©2016 Raj Jain 7-10 DS Spectrum Time Domain Frequency Domain Time Frequency (a) Data (b) Code Frequency Washington University in St. Louis http://www.cse.wustl.edu/~jain/cse473-16/ ©2016 Raj Jain 7-11 Two Sender CDMA Example Washington University in St. Louis http://www.cse.wustl.edu/~jain/cse473-16/ ©2016 Raj Jain 7-12 Homework 7A q Two CDMA sender use the codes of (1, -1, 1, -1) and (-1, 1, -1, 1). First sender transmits data bit 1 while the 2nd transmits –1 at the same time. What is the combined signal waveform seen by a receiver? Draw the waveform. Washington University in St. Louis http://www.cse.wustl.edu/~jain/cse473-16/ ©2016 Raj Jain 7-13 Frequency Hopping Spread Spectrum Frequency 50 ms Time q Pseudo-random frequency hopping q Spreads the power over a wide spectrum ⇒ Spread Spectrum q Developed initially for military q Patented by actress Hedy Lamarr (1942) q Narrowband interference can't jam Washington University in St. Louis http://www.cse.wustl.edu/~jain/cse473-16/ ©2016 Raj Jain 7-14 Spectrum Signal Noise Noise Signal (a) Normal (b) Frequency Hopping Washington University in St. Louis http://www.cse.wustl.edu/~jain/cse473-16/ ©2016 Raj Jain 7-15 Review: Wireless Link Characteristics 1. Wireless is not the same as mobile. However, most mobile nodes are wireless. 2. Wireless signal is affected by shadows, multipath, interference, Doppler shift 3. A wireless network can be ad-hoc or infrastructure based. 4. Multi-hop ad-hoc networks are called MANET 5. It is not possible to do collision detection in wireless 6. Code division multiple access is commonly used in wireless Ref: Section 7.2, Review Exercises R3-R4 Washington University in St. Louis http://www.cse.wustl.edu/~jain/cse473-16/ ©2016 Raj Jain 7-16 Overview Wireless LANs and PANs q IEEE 802.11 Wireless LAN PHYs q 4-Way Handshake q IEEE 802.11 MAC q 802.11 Frame Format q 802.11 Frame Addressing q 802.11 Rate Adaptation q Power Management q IEEE 802.15.4 q IEEE 802.15.4 MAC q ZigBee Overview Washington University in St. Louis http://www.cse.wustl.edu/~jain/cse473-16/ ©2016 Raj Jain 7-17 IEEE 802.11 Wireless LAN PHYs q 802.11: 2.4 GHz, 1-2 Mbps q 802.11b: 2.4 GHz, 11 Mbps nominal q Direct sequence spread spectrum (DSSS) in physical layer q All hosts use the same chipping code q 802.11a: 5.8 GHz band, 54 Mbps nominal q 802.11g: 2.4 GHz band, 54 Mbps nominal q 802.11n: 2.4 or 5.8 GHz, Multiple antennae, up to 200 Mbps q These are different PHY layers. All have the same MAC layer. q All use CSMA/CA for multiple access q All have base-station and ad-hoc network versions q Supports multiple priorities q Supports time-critical and data traffic q Power management allows a node to doze off Washington University in St. Louis http://www.cse.wustl.edu/~jain/cse473-16/ ©2016 Raj Jain 7-18 802.11: Passive/Active Scanning BBS 1 BBS 2 BBS 1 BBS 2 AP 1 AP 2 AP 1 1 AP 2 1 1 2 2 2 3 3 4 H1 H1 Passive Scanning: Active Scanning: (1) Beacon frames sent from APs (1) Probe Request frame broadcast (2) Association Request frame sent: H1 to from H1 selected AP (2) Probes response frame sent from APs (3) Association Response frame sent: (3) Association Request frame sent: H1 selected AP to H1 to selected AP (4) Association Response frame sent: selected AP to H1 Washington University in St. Louis http://www.cse.wustl.edu/~jain/cse473-16/ ©2016 Raj Jain 7-19 4-Way Handshake Access Mobile Point Node Ready to send Clear to send Data Ack Washington University in St. Louis http://www.cse.wustl.edu/~jain/cse473-16/ ©2016 Raj Jain 7-20 IEEE 802.11 MAC q Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) q Listen before you talk. If the medium is busy, the transmitter backs off for a random period. q Avoids collision by sending a short message: Ready to send (RTS) RTS contains dest. address and duration of message. Tells everyone to backoff for the duration. q Destination sends: Clear to send (CTS) q Can not detect collision ⇒ Each packet is acked. q MAC level retransmission if not acked. Washington University in St. Louis http://www.cse.wustl.edu/~jain/cse473-16/ ©2016 Raj Jain 7-21 IEEE 802.11 Architecture Server Access Access Ad-hoc Point Point Station Station Ad-hoc Station Station Station Station Basic Service Set 2nd BSS Ad-hoc network Washington University in St. Louis http://www.cse.wustl.edu/~jain/cse473-16/ ©2016 Raj Jain 7-22 Architecture (Cont.) q Basic Service Area (BSA) = Cell q Each BSA may have several wireless LANs q Extended Service Area (ESA) = Multiple BSAs interconnected via Access Points (AP) q Basic Service Set (BSS) = Set of stations associated with an AP q Extended Service Set (ESS) = Set of stations in an ESA q Ad-hoc networks coexist and interoperate with infrastructure-based networks.