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Computer networks

Computer networks . Guided Transmission Data. Twisted Pair Coaxial Cable Fiber Optics. Twisted Pair. (a) Category 3 UTP. (b) Category 5 UTP. Coaxial Cable. A coaxial cable. Fiber Cables. (a) Side view of a single fiber. (b) End view of a sheath with three fibers.

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Computer networks

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  1. Computer networks 6: Wireless and Mobile Networks

  2. Guided Transmission Data • Twisted Pair • Coaxial Cable • Fiber Optics 6: Wireless and Mobile Networks

  3. Twisted Pair (a) Category 3 UTP. (b) Category 5 UTP. 6: Wireless and Mobile Networks

  4. Coaxial Cable A coaxial cable. 6: Wireless and Mobile Networks

  5. Fiber Cables (a) Side view of a single fiber. (b) End view of a sheath with three fibers. 6: Wireless and Mobile Networks

  6. Fiber Cables (2) A comparison of semiconductor diodes and LEDs as light sources. 6: Wireless and Mobile Networks

  7. The Electromagnetic Spectrum The electromagnetic spectrum and its uses for communication. 6: Wireless and Mobile Networks

  8. Radio Transmission (a) In the VLF, LF, and MF bands, radio waves follow the curvature of the earth. (b) In the HF band, they bounce off the ionosphere. 6: Wireless and Mobile Networks

  9. The Mobile Telephone System • First-Generation Mobile Phones: Analog Voice • Second-Generation Mobile Phones: Digital Voice • Third-Generation Mobile Phones:Digital Voice and Data 6: Wireless and Mobile Networks

  10. Advanced Mobile Phone System (a) Frequencies are not reused in adjacent cells. (b) To add more users, smaller cells can be used. 6: Wireless and Mobile Networks

  11. GSMGlobal System for Mobile Communications GSM uses 124 frequency channels, each of which uses an eight-slot TDM system 6: Wireless and Mobile Networks

  12. GSM (2) A portion of the GSM framing structure. 6: Wireless and Mobile Networks

  13. wireless hosts • laptop, PDA, IP phone • run applications • may be stationary (non-mobile) or mobile • wireless does not always mean mobility network infrastructure Elements of a wireless network 6: Wireless and Mobile Networks

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

  15. network infrastructure Elements of a wireless network wireless link • typically used to connect mobile(s) to base station • also used as backbone link • multiple access protocol coordinates link access • various data rates, transmission distance 6: Wireless and Mobile Networks

  16. Characteristics of selected wireless link standards 200 802.11n 54 802.11a,g data 5-11 802.11b 802.16 (WiMAX) 3G cellular enhanced 4 UMTS/WCDMA-HSPDA, CDMA2000-1xEVDO Data rate (Mbps) 1 802.15 .384 3G UMTS/WCDMA, CDMA2000 2G .056 IS-95, CDMA, GSM Indoor 10-30m Outdoor 50-200m Mid-range outdoor 200m – 4 Km Long-range outdoor 5Km – 20 Km 6: Wireless and Mobile Networks

  17. infrastructure mode • base station connects mobiles into wired network • handoff: mobile changes base station providing connection into wired network network infrastructure Elements of a wireless network 6: Wireless and Mobile Networks

  18. Elements of a wireless network ad hoc mode • no base stations • nodes can only transmit to other nodes within link coverage • nodes organize themselves into a network: route among themselves 6: Wireless and Mobile Networks

  19. 802.11b 2.4-5 GHz unlicensed spectrum up to 11 Mbps 802.11a 5-6 GHz range up to 54 Mbps 802.11g 2.4-5 GHz range up to 54 Mbps 802.11n: multiple antennae 2.4-5 GHz range up to 200 Mbps IEEE 802.11 Wireless LAN 6: Wireless and Mobile Networks

  20. AP AP Internet 802.11 LAN architecture • wireless host communicates with base station • base station = access point (AP) • Basic Service Set (BSS) (aka “cell”) in infrastructure mode contains: • wireless hosts • access point (AP): base station • ad hoc mode: hosts only hub, switch or router BSS 1 BSS 2 6: Wireless and Mobile Networks

  21. 802.11: Channels, association • 802.11b: 2.4GHz-2.485GHz spectrum divided into 11 channels at different frequencies • AP admin chooses frequency for AP • interference possible: channel can be same as that chosen by neighboring AP! • host: must associate with an AP • scans channels, listening for beacon frames containing AP’s name (SSID) and MAC address • selects AP to associate with • may perform authentication [Chapter 8] • will typically run DHCP to get IP address in AP’s subnet 6: Wireless and Mobile Networks

  22. 4 2 2 2 3 3 1 1 1 802.11: passive/active scanning BBS 1 BBS 1 BBS 2 BBS 2 AP 1 AP 1 AP 2 AP 2 H1 H1 • Active Scanning: • Probe Request frame broadcast from H1 • Probes response frame sent from APs • Association Request frame sent: H1 to selected AP • Association Response frame sent: H1 to selected AP • Passive Scanning: • beacon frames sent from APs • association Request frame sent: H1 to selected AP • association Response frame sent: H1 to selected AP 6: Wireless and Mobile Networks

  23. P P P P P M M Master device Slave device Parked device (inactive) S S S S 802.15: personal area network • less than 10 m diameter • replacement for cables (mouse, keyboard, headphones) • ad hoc: no infrastructure • master/slaves: • slaves request permission to send (to master) • master grants requests • 802.15: evolved from Bluetooth specification • 2.4-2.5 GHz radio band • up to 721 kbps radius of coverage 6: Wireless and Mobile Networks

  24. 802.16: WiMAX point-to-point • like 802.11 & cellular: base station model • transmissions to/from base station by hosts with omnidirectional antenna • base station-to-base station backhaul with point-to-point antenna • unlike 802.11: • range ~ 6 miles (“city rather than coffee shop”) • ~14 Mbps point-to-multipoint 6: Wireless and Mobile Networks

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