20-09-2012, 04:37 PM
Wi-Fi Technology
WIFI_MONI.ppt (Size: 770 KB / Downloads: 25)
Introduction
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.
DSSS
Direct sequence signaling technique divides the 2.4 GHz band into 11 22-MHz channels. Adjacent channels overlap one another partially, with three of the 11 being completely non-overlapping. Data is sent across one of these 22 MHz channels without hopping to other channels.
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.
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
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.
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Introduction
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.
DSSS
Direct sequence signaling technique divides the 2.4 GHz band into 11 22-MHz channels. Adjacent channels overlap one another partially, with three of the 11 being completely non-overlapping. Data is sent across one of these 22 MHz channels without hopping to other channels.
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.
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
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.