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802.11 Wireless LAN

WLAN Technologies. 802.11 Wireless LAN. Provides network connectivity over wireless media An Access Point (AP) is installed to act as Bridge between Wireless and Wired Network The AP is connected to wired network and is equipped with antennae to provide wireless connectivity. Desktop

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802.11 Wireless LAN

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  1. WLAN Technologies 802.11 Wireless LAN • Provides network connectivity over wireless media • An Access Point (AP) is installed to act as Bridge between Wireless and Wired Network • The AP is connected to wired network and is equipped with antennae to provide wireless connectivity Desktop with PCI 802.11 LAN card Network connectivity to the legacy wired LAN Access Point Laptop with PCMCIA 802.11 LAN card

  2. WLAN Technologies 802.11 Wireless LAN • Range ( Distance between Access Point and WLAN client) depends on structural hindrances and RF gain of the antenna at the Access Point • To service larger areas, multiple APs may be installed with a 20-30% overlap • A client is always associated with one AP and when the client moves closer to another AP, it associates with the new AP (Hand-Off) • Five flavors: • 802.11b • 802.11a • 802.11g • 802.11n • 802.11ac

  3. WLAN Technologies Multiple Access with Collision Avoidance (MACA) • Before every data transmission • Sender sends a Request to Send (RTS) frame containing the length of the transmission • Receiver respond with a Clear to Send (CTS) frame • Sender sends data • Receiver sends an ACK; now another sender can send data • When sender doesn’t get a CTS back, it assumes collision other node in sender’s range other node in receiver’s range sender receiver RTS CTS data ACK

  4. WLAN Technologies WLAN : 802.11b • The first 802.11 standard deployed. • Supports 1, 2, 5.5 and 11 Mbps data rates in the 2.4 GHz ISM (Industrial-Scientific-Medical) band

  5. WLAN Technologies WLAN : 802.11a • Operates in the 5 GHz UNII (Unlicensed National Information Infrastructure) band • Incompatible with devices operating in 2.4GHz • Supports Data rates up to 54 Mbps (6,9,12,18,24,36,48,54 Mbps).

  6. WLAN Technologies WLAN : 802.11g • Supports data rates as high as 54 Mbps on the 2.4 GHz band • Provides backward compatibility with 802.11b equipment • Supports Data rates up to 54 Mbps (6,9,12,18,24,36,48,54 Mbps).

  7. WLAN Technologies WLAN : 802.11n • Supports data rates as high as 144 Mbps on the 2.4 GHz band (802.11g/n) and 300 Mbps on 5 GHz band (802.11a/n) for 2X2 stream • The maximum bandwidth per spatial stream in 802.11a/n is 150 Mbps, which means that an 802.11a/n AP outfitted with three transmit and three receive antennas can deliver maximum theoretical throughput of 450 Mbps • Supports upto 4 stream MIMO • Provides backward compatibility with 802.11a/b/g equipment

  8. WLAN Technologies WLAN : 802.11ac • Supports data rates as high as 1.3 Gbps (also called gigabit wireless) • Operates only in 5 GHz band • Supports 80/160 MHz channel • Supports upto 8 stream MIMO • The maximum bandwidth in 802.11ac is 433 Mbps per spatial stream, and the maximum number of spatial streams supported are eight. So the theoretical maximum throughput on an 802.11ac network will eventually be several times that of Gigabit Ethernet. First-generation devices (wave 1), however, are limited to using either two or three transmit and receive antennas to deliver a theoretical throughput maximum of 866 Mbps or 1.3 Gbps

  9. WLAN Technologies WLAN : MIMO • 802.11 a/b/g: Supports 54 Mbps on single 20 MHz stream • 802.11 n: Two stream 144 Mbps for 20MHz 2.4GHz band (802.11g/n) and 300 Mbps for 40 MHz 5GHz band (802.11a/n) or Three stream 450 Mbps for 40 MHz 5GHz band • 80211 ac: Three stream 1.3 Gbps for 80 MHz 5 Ghz band

  10. Assignment Assignment 4 • Why do you think that the CSMA/CD protocol of wired Ethernet is not used in Wi-Fi. • Find out the specs of Wi-Fi interface of your laptop and mobile phone (and iPad if you have one). Check the antenna specs also. • Find out the structure and role of beacon frames in Wi-Fi. • Do an ftp download (from ftp.iiitd.edu.in) of a large file (Linux ISO) using wired and wireless LAN. Compare the download speed with the maximum speed of the network connectivity. • Security is an important concern in Wi-Fi networks as it is very easy to sniff the wireless media. Find out how authentication and privacy (various encryption protocols) is supported in a typical Wi-Fi network. • A Wi-Fi client seamlessly roams across multiple APs without loosing network connectivity and session dropping. Find out how roaming works in Wi-Fi networks. • PoE is used to power Access Points from the network. Find out the specs and working of PoE and PoE+.

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