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Wireless LAN Standards

Wireless LAN Standards. MIS 4700 Dr. Garrett. IEEE. Institute of Electrical and Electronic Engineers (IEEE) Professional organization with members in engineering, science, and education Creates standards for the electronics, computer, and networking industries. IEEE 802 Standards.

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Wireless LAN Standards

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  1. Wireless LAN Standards MIS 4700 Dr. Garrett

  2. IEEE • Institute of Electrical and Electronic Engineers (IEEE) • Professional organization with members in engineering, science, and education • Creates standards for the electronics, computer, and networking industries

  3. IEEE 802 Standards

  4. IEEE 802 Committees • In February 1980, the IEEE formed a special committee to develop vendor-neutral standards for local area networks • Several subcommittees or task groups were formed to deal with specific networking issues

  5. IEEE 802 Committees

  6. IEEE 802 Wireless Standards

  7. IEEE 802.11 WLAN Standards

  8. WLAN Standards • Physical media • Frequency-hopping spread spectrum (FHSS) • Direct-sequence spread spectrum (DSSS) • Infrared (IR) • Media access control (MAC) functions

  9. IEEE 802.11 Wireless LAN Standards

  10. IEEE 802.11 Task Groups

  11. IEEE 802.11 Task Groups

  12. IEEE 802.11 Legacy

  13. The Original WLAN Standard • Released in 1997 as 802.11 • 1 or 2 Mbps • Infrared (IR) or radio frequency (RF) signals • 2.4 GHz band

  14. 802.11 MAC Layer • Manages and maintains communications between 802.11 transmitters and receivers by coordinating and controlling access to the shared RF channels • Operates on top of the 802.11x PHY layer

  15. The 802.11 MAC layer operates on top of the 802.11x PHY layer.

  16. Distributed Coordination Function • Wireless stations may not be in range of each other, so they cannot merely check to see if the medium is in use • Station calculates the time it will need to transmit the frame – the Navigation Allocation Vector (NAV) – and places it in the header of the frame • A station cannot transmit until they receive a NAV of zero • Also uses acknowledgement frames

  17. Point Coordination Function • Access point polls stations to see if they need to transmit • Stations may not transmit unless AP polls it • PCF remains idle if DCF is in use • Not implemented on many access points yet

  18. Required Scanning for signals Device authentication Network association Optional Data encryption RTS/CTS handshake Frame fragmentation Power conservation IEEE 802.11 MAC Layer Operations

  19. Passive scanning AP periodically broadcasts a beacon Used by wireless NICs to locate an AP and determine its signal strength Default, mandatory standard Active scanning Wireless NICs broadcast a probe frame APs within range respond Scanning for Signals

  20. Device Authentication • Mutual authentication occurs between a device and a network • Open systems authentication requires a wireless device to request authentication by sending an authentication request to an access point. • Shared-key authentication uses public encryption keys between stations

  21. Open System Authentication The exchange of frames in an open systems authentication process.

  22. Proprietary Authentication Methods • Lightweight Extensible Authentication Protocol (LEAP) is a Cisco proprietary authentication method using a centralized and user-based process • Wi-Fi Protected Access (WPA) is a vendor-neutral authentication process

  23. Man-In-The-Middle (MTTM) Attacks A man-in-the-middle (MTTM) attack occurs when an attacker is able to intercept, read, and perhaps modify frames transmitted between two stations, usually undetected.

  24. Network Association • Network association allows the NIC to synchronize with the access point and the bandwidth of the medium • Follows authentication • Once associated with an AP, the NIC can begin transmitting data frames

  25. Data Encryption • Wireless Equivalent Privacy (WEP) • Data of each frame is encrypted using a 40-bit encryption key known by sender and receiver

  26. RTS/CTS Handshake • Ready To Send / Clear To Send (RTS/CTS) handshake allows larger than normal data blocks to be sent • NIC sends a RTS to receiver • Receiver responds with a CTS and the time required to transmit the frame so other nodes know how long to wait before using the medium • Useful for hidden nodes

  27. RTS / CTS Handshake

  28. Hidden Node Nodes A and B are “hidden” from each other and must communicate through node C.

  29. Frame Fragmentation • Fragmentation allows a transmitting node to divide a data frame into smaller frames (fragments) • Useful when RF interference causes bit errors

  30. Power Conservation • Used in portable computers and devices • Allows the NIC to reduce its power requirements during idle periods and notify its access point that the NIC is switching to a sleep state • Access point buffers messages for the sleeping station until it is notified that the station is changing back to active state

  31. Signal Modulation • To use any kind of signal to represent data, the signal must be modulated • Common RF modulation methods are: • Amplitude modulation (AM) • Frequency modulation (FM) • Phase modulation (PM) • Data signal wave is inserted with a displacement relative to the carrier wave

  32. Phase Modulation A waveform has a 360-degree cycle length. An analog signal after a phase modulation of 90-degrees.

  33. IEEE 802.11b

  34. IEEE 802.11b WLAN Standard • Data rates of 5.5 Mbps and 11 Mbps • Operates on 2.4 GHz RF band • Infrastructure or ad-hoc mode

  35. 802.11b Physical (PHY) Layer • Uses Complementary Code Keying (CCK) with Quadrature Phase Shift Keying (QPSK) modulation • Uses Direct Sequence Spread Spectrum (DSSS) transmission • QAM combines two amplitude modulation (AM) signals onto a single channel • Dynamic rate shifting (DRS) allows the transmission rate to be adjusted to a lower rate when interference is experienced

  36. Physical Layer Convergence Protocol (PLCP) Performs the carrier sense using a Clear Channel Assessment Physical Medium Dependent (PMD) Defines transmit and receive functions such as type of modulation and spread spectrum used 802.11b PHY Sublayers

  37. 802.11b Infrastructure Mode • Includes at least one wireless station and one access point connected to a distribution system • Two possible configurations: • Basic Service Set (BSS) • Extended Service Set (ESS)

  38. Basic Service Set (BSS) • Wireless stations communicate with only one access point • The access point frequently serves as a bridge between the wireless stations and a distribution system like a wired network

  39. Extended Service Set (ESS) • Combines two or more BSSs

  40. 802.11b ad-hoc Mode • Uses and Independent Basic Service Set (IBSS) • Wireless stations communicate directly with each other • No base station, or AP • Peer-to-peer wireless network

  41. IEEE 802.11a

  42. 802.11a WLAN Standard • Defines the PHY and MAC layers • Uses orthogonal frequency division multiplexing (OFDM) • Orthogonal describes items that do not overlap, are mutually independent, and expand to fill an entire space • Up to 54 Mbps bandwidth • Uses 5 GHz RF band • Not compatible with 802.11b

  43. Orthogonal Frequency Division Multiplexing (OFDM) • Both a modulation and multiplexing technique • Divides a 20 MHz RF channel into 48 narrowband sub-channels and then splits a data signal into 48 separate carriers • Subchannels overlap and signal bits are sent in parallel using frequency division multiplexing

  44. FDM and OFDM Comparison A comparison of how FDM and OFDM modulate a signal for transmission.

  45. Multi-path Propagation • Multi-path propagation occurs when an RF signal cannot take a clear and direct path between a transmitter and a receiver • Some signals are delayed more than others and may overlap another signal arriving at the receiver, called inter-symbol interference

  46. IEEE 802.11IR

  47. IEEE 802.11IR Standard • Transmission method that uses optical diffusion • 1 Mbps or 2 Mbps bandwidth • Bounces IR signals off walls and ceilings

  48. Advantages Security: IR signal does not leave the room but may go through a window Not susceptible to RF interference Disadvantages IR light transmissions are limited to a single room, so an access point is required in each room Compatibility is an issue with some products on the market 802.11IR Advantages and Disadvantages

  49. Cutting Edge IEEE 802.11x Standards

  50. 802.11g Standard • Compatible with 802.11b and Wi-Fi standards • Data rates up to 54 Mbps • Transmits over three channels • 802.11a+g products are beginning to come out that provide compatibility with 802.11a also

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