Wireless LAN Basics

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The 802.3 family is for Ethernet LANs and the 802.11 family is for WLANs. Both standards define a frame format with a header and a trailer, with the header including a source and destination MAC address field, each 6 bytes in length. WLANs use radiated energy waves, generally called radio waves, to transmit data, whereas Ethernet uses electrical signal flowing over a cable (or light on optical cabling). If two wireless devices send radio waves in the same space as the same frequency, neither signal is intelligible, so a half – duplex (HDX) mechanism must be used. WLANs use the carrier sense multiple access with collision avoidance (CSMA/CA) algorithm to enforce HDX logic.

Wireless-capable devices communicate with a connector WLAN device called an access point (AP) to send and receive frames. APs connect WLAN clients (connecting devices) with Ethernet LAN or internet as implemented.

IEEE introduced WLAN standards with the creation of the 1997 ratification of the 802.11 standard which was replaced by more-advanced standards of 802.11b, 802.11a, and 802.11g as per order of ratification. The WLAN standards are described in the table below as

Feature	802.11 a	802.11 b	802.11 g
DSSS speed		11 Mbps	11 Mbps
OFDM speed	54 Mbps		54 Mbps
Non-overlapping Channels	12	3	3
Total Channels	23	11	11
Frequency Bands	5 GHz	2.4 GHz	2.4 GHz

WLANs work in either of two modes as

• Ad Hoc Mode – A wireless device communicates directly with another for a short period.
• Infrastructure Mode – Each device communicates with an AP, which connects to a wired Ethernet.

Devices in infrastructure WLAN sends frames to the AP and not directly to each other and hence, also called as the Independent Basic Service Set (IBSS). Infrastructure mode supports service sets

• Basic Service Set (BSS) – uses a single AP to create the WLAN and users move inside the coverage area.
• Extended Service Set (ESS) – uses more than one AP, with overlapping cells to allow roaming in a larger area.

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