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Wireless LAN

Wireless LAN. presented by: Damian Borth, Florian Seidel, Thomas Winterscheid. Contents. Definition The IEEE 802.11 standards Infrastructure and Impairments Hardware System Providers Advantages and Disadvantages Security Alternatives. Table of content. IEEE Standard 802.11 Basics

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Wireless LAN

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  1. Wireless LAN presented by: Damian Borth, Florian Seidel, Thomas Winterscheid

  2. Contents • Definition • The IEEE 802.11 standards • Infrastructure and Impairments • Hardware • System Providers • Advantages and Disadvantages • Security • Alternatives

  3. Table of content • IEEE Standard 802.11 • Basics • Frequency • OSI / ISO Layer • Modulation • Net topology • Properties

  4. Standard • There is the IEEE 802.11 Standard for WLAN`s • Sub specifications • 802.11a • 802.11b • 802.11g • 802.11e

  5. Basics • OSI / ISO overview • Physical Layer • Wireless LAN is almost exclusively Spread Spectrum Radio • direct sequence spread spectrum (DSSS) • frequency-hopping spread spectrum (FHSS) • infrared pulse position modulation (IrDA) • Data Link Layer • Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol

  6. Basics • Frequence • ISM band 2.4 GHz and 5 GHz • 2.4 - 2.4835 GHz frequency band • 5.725 - 5.850 GHz frequency band • Modus • Ad hoc mode • Peer to peer • Infrastructure mode • Using an access point network

  7. Properties • Range: 100m – 400m (outdoors) • 802.11b- DSSS @11Mbps 2.4GHz • 802.11a- DSSS @54Mbps 5GHz • 802.11g- DSSS @22Mbps 2.4GHz • 802.11e- DSSS @22Mbps w/QoS

  8. Contents (Part 2) • Definition • The IEEE 802.11 standards • Infrastructure and Impairments • Hardware • System Providers • Advantages and Disadvantages • Security • Alternatives

  9. How to install? • Two different use modes: • AdHoc (P2P) • Infrastructured (LAN) ? ? ? ?

  10. Adhoc • Standard P2P connection • Only for two PC`s • Same way of configuration (IP range etc...) • Transferrate 11 Mbit/s • Range ca. 30m-50m (outdoor 400m) • WEP against eavesdropping

  11. Infrastructured • Access points are needed • Range 30m - 50m • Access points act like bridges/gateways • Installation of access points enables „Roaming“ functionality • Configuration of IP and administration like in wired network • Transferrate 11 Mbit/s

  12. Impairments • Weakened by solid walls and concrete • No influence through glass • Range impairment can be increased with additional antenna up to 2 km • Bluetooth / IrDA

  13. Which hardware you need? e.g. Fujitsu-Siemens I-Gate WLAN WirelessLan-Card Pre-installed Adapter USB Access Point

  14. Wired? • Connectivity to wired LAN • Access points must be installed (bridge functionality) • Connectable to each kind of LAN

  15. Roaming • Extended connectivity possibility • Allows free mobility • Access points transfers given IP within the network • Roaming between different networks is also possible (bridge/gateway)

  16. Access to WAN? • ...is possible by using access points connected to ISDN / DSL • Access points can act like a gateway • No impairment to the transferrates

  17. Producer Fujitsu-Siemens Aironet NDC  Proxim Bay Networks Lucent RDC Productname I-Gate Telxon Serie 3500 Instantwave Rangelan Airsurfer Wavelan Portlan System provider

  18. Contents (Part 3) • Definition • The IEEE 802.11 standards • Infrastructure and Impairments • Hardware • System Providers • Advantages and Disadvantages • Security • Alternatives

  19. Advantages • mobility / flexibility • inexpensiveness • ease of installation / usage • extends LAN and doesn’t need to replace it

  20. Disadvantages • lack of security • lower transmission rates than in wired networks

  21. Security • basic problem: broadcast of radio data transmission • piracy tools: • AirSnort • WEPcrack • Network Stumbler, etc. • real problem: default settings of WLAN are insecure, e.g. „Accept ANY SSID“

  22. Security - WEP • Wireless Equivalent Privacy • based on RC4 encryption algorithm • most important, but optional • 128 bit encryption algorithm for data encryption and authentification

  23. Security - WEP • WEP does stream-encryption + generates key for each data package • to set up the stream, WEP uses the shared key and an initialization vector • the plain text information is parsed bit-by-bit and combined with pseudo random numbers (ensures that packages with same content are not equally encrypted)

  24. Security - WEP • a carrier frequency is determined by the constallation of the data stream and broadcasted throughout the WLAN • the recipient deletes the pseudo random numbers and restores the plain text information

  25. Weak Point • Initialization Vector (IV) • 24 bit • easily predictable (usually increment by1) • Same IV + (constant) Shared Key  IV-Collision (same WEP-Key) • many IV-Collisions allow extraction

  26. Security check • change default settings (e.g. password) • use WEP encryption • change WEP key regularly • filter MAC addresses • position APs before firewall

  27. Security check • check log files for intrusion attempts • use “intrusion detection system” • turn off DHCP • use authentification • for extra high security use a VPN.

  28. References & Bibliography • http://www.ieee.org • http://www.tecchannel.de • http://www.fujitsu-siemens.de • “Data and Computer Communications”,Sixth Edition, William Stallings, Prentice Hall

  29. Any Questions? Thank you.

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