05-11-2012, 06:11 PM
Wi-Fi Technology
1Wi-Fi.ppt (Size: 362 KB / Downloads: 48)
Wi-Fi Technology
Wireless Technology is an alternative to Wired Technology, which is commonly used, for connecting devices in wireless mode.
Wi-Fi (Wireless Fidelity) is a generic term that refers to the IEEE 802.11 communications standard for Wireless Local Area Networks (WLANs).
Wi-Fi Network connect computers to each other, to the internet and to the wired network.
IEEE 802.11b
Appear in late 1999
Operates at 2.4GHz radio spectrum
11 Mbps (theoretical speed) - within 30 m Range
4-6 Mbps (actual speed)
100 -150 feet range
Most popular, Least Expensive
Interference from mobile phones and Bluetooth devices which can reduce the transmission speed.
802.11 Physical Layer
There are three sublayers in physical layer:
Direct Sequence Spread Spectrum (DSSS)
Frequency Hoping Spread Spectrum (FHSS)
Diffused Infrared (DFIR) - Wide angle
IEEE 802.11 Data Link Layer
The data link layer consists of two sublayers :
Logical Link Control (LLC)
Media Access Control (MAC).
802.11 uses the same 802.2 LLC and 48-bit addressing as other 802 LANs, allowing for very simple bridging from wireless to IEEE wired networks, but the MAC is unique to WLANs.
802.11 Media Access Control
Carrier Sense Medium Access with collision avoidance protocol (CSMA/CA)
Listen before talking
Avoid collision by explicit Acknowledgement (ACK)
Problem: additional overhead of ACK packets, so slow performance
Request to Send/Clear to Send (RTS/CTS) protocol
Solution for “hidden node” problem
Problem: Adds additional overhead by temporarily reserving the medium, so used for large size packets only retransmission would be expensive
Power Management
MAC supports power conservation to extend the battery life of portable devices
Power utilization modes
Continuous Aware Mode
Radio is always on and drawing power
Power Save Polling Mode
Radio is “dozing” with access point queuing any data for it
The client radio will wake up periodically in time to receive regular beacon signals from the access point.
The beacon includes information regarding which stations have traffic waiting for them
The client awake on beacon notification and receive its data
How a Wi-Fi Network Works
Basic concept is same as Walkie talkies.
A Wi-Fi hotspot is created by installing an access point to an internet connection.
An access point acts as a base station.
When Wi-Fi enabled device encounters a hotspot the device can then connect to that network wirelessly.
A single access point can support up to 30 users and can function within a range of 100 – 150 feet indoors and up to 300 feet outdoors.
Many access points can be connected to each other via Ethernet cables to create a single large network.
Point-to-multipoint bridge topology
This is used to connect a LAN in one building to a LANs in other buildings even if the buildings are miles apart.These conditions receive a clear line of sight between buildings. The line-of-sight range varies based on the type of wireless bridge and antenna used as well as the environmental conditions.
Eavesdropping
Easy to perform, almost impossible to detect
By default, everything is transmitted in clear text
Usernames, passwords, content ...
No security offered by the transmission medium
Different tools available on the internet
Network sniffers, protocol analysers . . .
Password collectors
With the right equipment, it’s possible to eavesdrop traffic from few kilometers away
Wired Equivalent Privacy (WEP)
Provide same level of security as by wired network
Original security solution offered by the IEEE 802.11 standard
Uses RC4 encryption with pre-shared keys and 24 bit initialization vectors (IV)
key schedule is generated by concatenating the shared secret key with a random generated 24-bit IV
32 bit ICV (Integrity check value)
No. of bits in keyschedule is equal to sum of length of the plaintext and ICV
1Wi-Fi.ppt (Size: 362 KB / Downloads: 48)
Wi-Fi Technology
Wireless Technology is an alternative to Wired Technology, which is commonly used, for connecting devices in wireless mode.
Wi-Fi (Wireless Fidelity) is a generic term that refers to the IEEE 802.11 communications standard for Wireless Local Area Networks (WLANs).
Wi-Fi Network connect computers to each other, to the internet and to the wired network.
IEEE 802.11b
Appear in late 1999
Operates at 2.4GHz radio spectrum
11 Mbps (theoretical speed) - within 30 m Range
4-6 Mbps (actual speed)
100 -150 feet range
Most popular, Least Expensive
Interference from mobile phones and Bluetooth devices which can reduce the transmission speed.
802.11 Physical Layer
There are three sublayers in physical layer:
Direct Sequence Spread Spectrum (DSSS)
Frequency Hoping Spread Spectrum (FHSS)
Diffused Infrared (DFIR) - Wide angle
IEEE 802.11 Data Link Layer
The data link layer consists of two sublayers :
Logical Link Control (LLC)
Media Access Control (MAC).
802.11 uses the same 802.2 LLC and 48-bit addressing as other 802 LANs, allowing for very simple bridging from wireless to IEEE wired networks, but the MAC is unique to WLANs.
802.11 Media Access Control
Carrier Sense Medium Access with collision avoidance protocol (CSMA/CA)
Listen before talking
Avoid collision by explicit Acknowledgement (ACK)
Problem: additional overhead of ACK packets, so slow performance
Request to Send/Clear to Send (RTS/CTS) protocol
Solution for “hidden node” problem
Problem: Adds additional overhead by temporarily reserving the medium, so used for large size packets only retransmission would be expensive
Power Management
MAC supports power conservation to extend the battery life of portable devices
Power utilization modes
Continuous Aware Mode
Radio is always on and drawing power
Power Save Polling Mode
Radio is “dozing” with access point queuing any data for it
The client radio will wake up periodically in time to receive regular beacon signals from the access point.
The beacon includes information regarding which stations have traffic waiting for them
The client awake on beacon notification and receive its data
How a Wi-Fi Network Works
Basic concept is same as Walkie talkies.
A Wi-Fi hotspot is created by installing an access point to an internet connection.
An access point acts as a base station.
When Wi-Fi enabled device encounters a hotspot the device can then connect to that network wirelessly.
A single access point can support up to 30 users and can function within a range of 100 – 150 feet indoors and up to 300 feet outdoors.
Many access points can be connected to each other via Ethernet cables to create a single large network.
Point-to-multipoint bridge topology
This is used to connect a LAN in one building to a LANs in other buildings even if the buildings are miles apart.These conditions receive a clear line of sight between buildings. The line-of-sight range varies based on the type of wireless bridge and antenna used as well as the environmental conditions.
Eavesdropping
Easy to perform, almost impossible to detect
By default, everything is transmitted in clear text
Usernames, passwords, content ...
No security offered by the transmission medium
Different tools available on the internet
Network sniffers, protocol analysers . . .
Password collectors
With the right equipment, it’s possible to eavesdrop traffic from few kilometers away
Wired Equivalent Privacy (WEP)
Provide same level of security as by wired network
Original security solution offered by the IEEE 802.11 standard
Uses RC4 encryption with pre-shared keys and 24 bit initialization vectors (IV)
key schedule is generated by concatenating the shared secret key with a random generated 24-bit IV
32 bit ICV (Integrity check value)
No. of bits in keyschedule is equal to sum of length of the plaintext and ICV