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

Contents Definition The IEEE standards Infrastructure and Impairments Hardware System Providers Advantages and Disadvantages Security Alternatives

Table of content IEEE Standard Basics Frequency OSI / ISO Layer Modulation Net topology Properties

Standard There is the IEEE Standard for WLAN`s Sub specifications a b g e

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

Basics Frequence ISM band 2.4 GHz and 5 GHz GHz frequency band GHz frequency band Modus Ad hoc mode Peer to peer Infrastructure mode Using an access point network

Properties Range: 100m – 400m (outdoors) b- 2.4GHz a- 5GHz g- 2.4GHz e- w/QoS

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

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

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

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

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

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

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

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

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

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

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

Advantages mobility / flexibility inexpensiveness ease of installation / usage extends LAN and doesnt need to replace it

Disadvantages lack of security lower transmission rates than in wired networks

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

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

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)

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

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

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

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

Standards Overview

References & Bibliography Data and Computer Communications,Sixth Edition, William Stallings, Prentice Hall

Any Questions? Thank you.