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Network Operations & administration CS 4592 Lecture 21

Network Operations & administration CS 4592 Lecture 21. Instructor: Ibrahim Tariq. IEEE 802 Series of LAN Standards. 802 standards free to download from http://standards.ieee.org /getieee802. WiMAX. IEEE 802.11 Wireless LAN - 1. Wireless LANs IEEE 802.11 standard:

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Network Operations & administration CS 4592 Lecture 21

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  1. Network Operations & administration CS 4592Lecture 21 Instructor: Ibrahim Tariq

  2. IEEE 802 Series of LAN Standards • 802 standards free to download from http://standards.ieee.org/getieee802 WiMAX

  3. IEEE 802.11 Wireless LAN - 1 • Wireless LANs • IEEE 802.11 standard: • unlicensed frequency spectrum: 900Mhz, 2.4Ghz

  4. Figure 14.1 Basic service sets (BSSs)

  5. IEEE 802.11 Wireless LAN - 2 • Basic Service Set (BSS) (a.k.a. “cell”) contains: • wireless hosts • access point (AP): base station • BSS’s combined to form distribution system (DS)

  6. Figure 14.2 Extended service sets (ESSs)

  7. Ad Hoc Networks • Ad hoc network: IEEE 802.11 stations can dynamically form networkwithoutAP • Applications: • “laptop” meeting in conference room, car • interconnection of “personal” devices • battlefield • IETF MANET (Mobile Ad hoc Networks) working group

  8. IEEE 802.11 MAC Protocol: CSMA/CA 802.11 CSMA sender: - if sense channel idle for DISF sec. then transmit entire frame (no collision detection) -if sense channel busy then binary backoff 802.11 CSMA receiver: if received OK return ACK after SIFS

  9. Hidden Terminal effect • hidden terminals: A, C cannot hear each other • obstacles, signal attenuation • collisions at B • goal: avoid collisions at B • CSMA/CA: CSMA with Collision Avoidance

  10. Hidden Station Problem • The CTS frame in CSMA/CA handshake can prevent collision from a hidden station.

  11. Use of Handshaking to Prevent Hidden Station Problem

  12. Collision Avoidance: RTS-CTS exchange - 1 • CSMA/CA: explicit channel reservation • sender: send short RTS: request to send • receiver: reply with short CTS: clear to send • CTS reserves channel for sender, notifying (possibly hidden) stations • Avoid hidden station collisions

  13. Collision Avoidance: RTS-CTS exchange - 2 • RTS and CTS short: • collisions less likely, of shorter duration • end result similar to collision detection • IEEE 802.11 allows: • CSMA • CSMA/CA: reservations • polling from AP

  14. Exposed Station Problem

  15. Use of handshaking in exposed station problem

  16. Interconnecting Devices Data Communication & Networks, Fall 2009

  17. 14-2 BLUETOOTH Bluetooth is a wireless LAN technology designed to connect devices of different functions such as telephones, notebooks, computers, cameras, printers, coffee makers, and so on. A Bluetooth LAN is an ad hoc network, which means that the network is formed spontaneously. Topics discussed in this section: ArchitectureBluetooth LayersBaseband Layer L2CAP

  18. Figure 14.19 Piconet

  19. Figure 14.20 Scatternet

  20. Figure 14.21 Bluetooth layers

  21. Interconnecting Devices • How to get more users attached to a LAN? • How to extend a single LAN? • How to connect different LANs? Data Communication & Networks, Fall 2009

  22. Interconnecting Devices (cnt’d) • Repeater • Hub • Bridge • Switch • Router Data Communication & Networks, Fall 2009

  23. Five Categories of Network Devices Data Communication & Networks, Fall 2009

  24. Repeater • works at the Physical layer • Regenerates received bits before it sends them out • connects different half-duplex network segments • either extends the number of users or the total span (by improving the quality of the transmitted signal) Data Communication & Networks, Fall 2009

  25. A Repeater Connects two segments of LAN Data Communication & Networks, Fall 2009

  26. Function of Repeater Data Communication & Networks, Fall 2009

  27. Note A repeater is a regenerator, not an amplifier. Data Communication & Networks, Fall 2009

  28. multi-port repeater (physical hardware device) provides physical star topology no intelligence no separations of collision domains all the hosts compete for the shared bandwidth Hub Data Communication & Networks, Fall 2009

  29. HUB • An Ethernet hub, active hub, network hub, repeater hub or hub is a device for connecting multiple Ethernet devices together and making them act as a single network segment. A hub works at the physical layer (layer 1) of the OSI model • The device is a form of multiport repeater.

  30. Bridge • works at layer 2 (requires software) • connects two networks of the same type • LAN to LAN (example: WLAN to Fast Ethernet) • forwards data (1 packet @ the time) depending on the destination address in the data packet (not the IP address, but the physical (MAC) address that is unique for every Network Interface Card (NIC)) • all computers are in the same sub-network • packet filtering • separates collision domains – larger network spans • a stand alone device or a PC with the special NIC and the accompanied software Data Communication & Networks, Fall 2009

  31. Bridge (cnt’d) Data Communication & Networks, Fall 2009

  32. Note A bridge has a table used in filtering decisions. Data Communication & Networks, Fall 2009

  33. Note A bridge does not change the physical (MAC) addresses in a frame. Data Communication & Networks, Fall 2009

  34. Switch • basically a multi-port bridge • provides a better network performance • forwards more than a single packet at a time • separates collision domains – larger total network span • bandwidth not shared Data Communication & Networks, Fall 2009

  35. Switch (cnt’d) Data Communication & Networks, Fall 2009

  36. Router • connects different sub-networks • Layer 3 (Network layer) device • forwarding based on IP addresses not on MAC addresses • more expensive than a switch (requires CPU) • Layer 3 switches (only work with IP packets) Data Communication & Networks, Fall 2009

  37. An Example a simple internet Data Communication & Networks, Fall 2009

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