Transcript 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

Frequency
 OSI / ISO Layer
 Modulation
 Net topology


Properties
Standard
There is the IEEE 802.11 Standard
for WLAN`s
 Sub specifications

802.11a
 802.11b
 802.11g
 802.11e

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
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
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

Contents (Part 2)
Definition
 The IEEE 802.11 standards
 Infrastructure and Impairments
 Hardware
 System Providers
 Advantages and Disadvantages
 Security
 Alternatives

How to install?

Two different use modes:
AdHoc (P2P)
 Infrastructured (LAN)

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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?
e.g. Fujitsu-Siemens
I-Gate WLAN
WirelessLan-Card
Pre-installed
Adapter USB
Access Point
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 802.11 standards
 Infrastructure and Impairments
 Hardware
 System Providers
 Advantages and Disadvantages
 Security
 Alternatives

Advantages
mobility / flexibility
 inexpensiveness
 ease of installation / usage
 extends LAN and doesn’t 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 bitby-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.
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

Any Questions?
Thank you.