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Ch 6. Wireless and Mobile Networks

Myungchul Kim mckim@icu.ac.kr. Ch 6. Wireless and Mobile Networks. Wirless hosts Wireless links Base station: (e.g., cell towers, access points) handoff Infrastructure mode Ad hoc mode. Wireless network taxonomy. multiple hops. single hop. host may have to relay through several

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Ch 6. Wireless and Mobile Networks

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  1. Myungchul Kim mckim@icu.ac.kr Ch 6. Wireless and Mobile Networks

  2. Wirless hosts • Wireless links • Base station: (e.g., cell towers, access points) handoff • Infrastructure mode • Ad hoc mode

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

  4. Wireless links and network characteristics • Differences between a wired link and a wireless link • Decreasing signal strength • Interference from other source • Multipath propagation • Signal-to-noise ration (SNR) • A relative measure of the strength of the received signal and the noise. • dB • Bit error rate (BER)

  5. Physical-layer characteristics of higher-layer wireless communication protocols • For a given modulation scheme, the higher the SNR, the lower the BER. • For a given SNR, a modulation technique with a higher bit transmission rate will have a higher BER. • Dynamic selection of the physical-layer modulation technique can be used to adapt the modulation technique to channel condition.

  6. CDMA • A partitioning protocol in that it partitions the codespace and assigns each node a dedicated piece of the codespace.

  7. WiFi: 802.11 Wireless LANs • 802.11n: multiple-input multiple-output (MIMO) antennas, over 100Mbps, compatible with 802.11a/b/g devices

  8. The 802.11 architecture • Basic service set (BSS): service set identifer (SSID)

  9. Channels and association • 11 partically overlapping channels • Separated by four channels (e.g., 1, 6, and 11) • AP sends beacon frames (AP’s SSID and MAC address)

  10. Association with authentication • A station’s MAC address • Usernames and passwds by RADIUS or DIAMETER • The 802.11 MAC protocol • CSMA/Collision Avoidance • Differences from Ethernet • Collision avoidance • Link-layer acknowledgement/retransmission • No collision detection • Costly to build hardware that can detect a collision • No detect all collisions due to the hidden terminal problem and fading

  11. Dealing with hidden terminals: RTS and CTS • RTS (including the total time required to transmit the DATA and the ACK) and CTS to reserve access to the channel • CTS: gives the sender explicit permission to send and also instructs the other stations not to send for the reserved duration. • RTS/CTS is used only when the frame is longer than the threshold.

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

  13. The IEEE 802.11 frame • The fourth address: APs forward frames to each other in ad hoc mode.

  14. Address 3 contains the MAC address of the router interface.

  15. router AP Internet R1 MAC addr AP MAC addr source address dest. address 802.3frame AP MAC addr H1 MAC addr R1 MAC addr address 3 address 2 address 1 802.11 frame 802.11 frame: addressing H1 R1

  16. Mobility in the same IP subnet

  17. Advanced features in 802.11 • 802.11 rate adaptation: select the underlying physical-layer modulation technique to use based on current channel characteristics. • Power management: alternate between sleep and wake states, 250 microseconds for wakeup. • Bluetooth • IEEE 802.15.1 • Wireless personal area network • 4Mbps • Ad hoc networks • A piconet of up to eight active devices

  18. WiMAX • IEEE 802.16 • Wireless ADSL • Speeds of 70-80 miles per hour

  19. Cellular Internet Access • Air interface access technologies • A combination of FDM and TDM • CDMA

  20. 1G • Analog FDMA • Voice only • 2G • Digital for voice • Global system for mobile communication (GSM) • Combined FDM/TDM • IS-95 CDMA • 2.5G • General packet radio service (GPRS): up to 9.6kbps packet-based data • Enhanced data rates for global evolution (EDGE): 384 kbps • CDMA-2000 phase: packet-data up to 144.4 kbps

  21. 3G • 144 kbps at driving speeds • 384 kbps for outside stationary use or walking speeds • 2 Mbps for indoors • CDMA-2000 • Evolved from IS-95 • 1xEVDO for 3 Mbps data • Universal Mobile Telecommunication Service (UMTS) • WCDMA for data • HSDPA/HSUPA up to 14 Mbps • 4G • Ubiquitout Internet access • The highest bit rate at that time and place • Vertical handoff • Seamless moblity • Voice and real-time video over IP

  22. Mobility management: principles

  23. Routing to a mobile node

  24. A mobile-node-to-foreign-agent protocol • A foreign-agent-to-home-agent registration protocol • A home-agent datagram encapsulation protocol • A foreign-agent decampsulation protocol • Direct routing to a mobile node • Triangle routing problem • A mobile-user location protocol • Anchor foreign agent

  25. Mobile IP • Agent discovery • Registration with the home agent • Indirect routing of datagrams • Agent discovery • Via agent advertisement or via agent solicitation • An extension to the router discovery protocol • Home agent bit (H), foreign agent bit (F), registration required bit (R), M and G encapsulation bits, care-of-address (COA) fields.

  26. Managing mobility in cellular networks • GSM • Indirect routing • Home location register (HLR), Visitor location register (VLR) • Mobile station roaming number

  27. Handoffs in GSM

  28. Mobile Switching Center 1 3 2 4 5 6 7 8 VLR GSM: handoff with common MSC 1. old BSS informs MSC of impending handoff, provides list of 1+ new BSSs 2. MSC sets up path (allocates resources) to new BSS 3. new BSS allocates radio channel for use by mobile 4. new BSS signals MSC, old BSS: ready 5. old BSS tells mobile: perform handoff to new BSS 6. mobile, new BSS signal to activate new channel 7. mobile signals via new BSS to MSC: handoff complete. MSC reroutes call 8 MSC-old-BSS resources released old BSS new BSS

  29. Wireless and mobility: impact on higher layer protocols • Packet loss in TCP • Network congestion • Handoff • Wireless communication • Approaches • Local recovery • TCP sender awareness of wireless links • Split-connection approaches: two tranport-layer connections

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