WLAN is half-duplex communication - everyone is sharing the same bandwidth and only one user is communicating at a time.
APs - access points
BSS - The Basic Service Set is a set of all stations that can communicate with each other
There are two types of BSS:
Every BSS has an identification (ID) called the BSSID, which is the MAC address of the access point servicing the BSS.
- Independent BSS ( also referred to as IBSS )
- Infrastructure BSS
ESS -an Extended Service Set is a set of connected BSSes
DS - Distribution System connects access points in an extended service set. The concept of a DS can be to increase network coverage through roaming between cells.
AD-Hoc - a decentralized wireless network, where each node is willing to forward data for other nodes, and so the determination of which nodes forward data is made dynamically based on the network connectivity. This is in contrast to wired networks in which routers perform the task of routing. It is also in contrast to managed (infrastructure) wireless networks, in which a special node known as an access point manages communication among other nodes.
SSID - a Service Set Identifier, is a name used to identify the particular 802.11 wireless LANs to which a user wants to attach. A client device will receive broadcast messages from all access points within range advertising their SSIDs, and can choose one to connect to based on pre-configuration, or by displaying a list of SSIDs in range and asking the user to select one.
Higher frequency - Higher data rate - Shorter distance
Main 802.11 standarts:
- A - 54 Mbps - 5 Ghz - 12 non-ov. ch. - 70 feet (20 m), at 6MB - 175 feet (55 m)
- B - 11 Mbps - 2.4 Ghz - 3 non-ov. ch. - 150 feet (45 m), at 1 MB - 350 feet (100 m)
- G - 54 Mbps - 2.4 Ghz - 3 non-ov. ch. - 100 feet (30 m), at 6MB - 300 feet (90 m)
- N - ?? Mbps - 2.4?? Ghz - ?? non-ov. ch. - ??? feet (??m), MIMO
- H - ?? Mbps - 5 Ghz - 23 non-ov. ch. - ??? feet (??m) Dynanic Fr. Selection & TPC Transmit Power Control
While 802.11b was in development, IEEE created a second extension to the original 802.11 standard called 802.11a. Because 802.11b gained in popularity much faster than did 802.11a, some folks believe that 802.11a was created after 802.11b. In fact, 802.11a was created at the same time. Due to its higher cost, 802.11a is usually found on business networks whereas 802.11b better serves the home market.
The newest IEEE standard in the Wi-Fi category is 802.11n. It was designed to improve on 802.11g in the amount of bandwidth supported by utilizing multiple wireless signals and antennas (called MIMO technology) instead of one.
Two types of authentication:
open authentication to supply the correct SSID
shared-key authentication : the access point sends the client device a challenge-text packet that the client must then encrypt with the correct Wired Equivalency Protocol (WEP) key and return to the access point.
WCS - Wireless Control System
LWAPP - Lighweight Access Point Protocol
WPA or WPA2 Pre-Shared Key (PSK)
TKIP - pronounced as tee-kip. This is part of the IEEE 802.11i standard. TKIP implements per-packet key mixing with a re-keying system and also provides a message integrity check. These avoid the problems of WEP.
AES - The Advanced Encryption Standard
WPA2 is based on the Robust Security Network (RSN) mechanism, which provided support for all of the mechanisms available in WPA, as well as:
As of March 2006, the WPA2 certification became mandatory for all new equipment certified by the Wi-Fi Alliance, ensuring that any reasonably modern hardware will support both WPA and WPA2.
- Strong encryption and authentication support for infrastructure and ad-hoc networks (WPA is limited to infrastructure networks);
- Reduced overhead in key derivation during the wireless LAN authentication exchange;
- Support for opportunistic key caching to reduce the overhead in roaming between access points;
- Support for pre-authentication, where a station completes the IEEE 802.1X authentication exchange before roaming;
- Support for the CCMP (Counter Mode with Cipher Block Chaining Message Authentication Code Protocol) encryption mechanism based on the Advanced Encryption Standard (AES) cipher as an alternative to the TKIP protocol.
Orthogonal frequency-division multiplexing (OFDM) - essentially identical to Coded OFDM (COFDM) and Discrete multi-tone modulation (DMT) - is a frequency-division multiplexing (FDM) scheme utilized as a digital multi-carrier modulation method. A large number of closely-spaced orthogonal sub-carriers are used to carry data. The data are divided into several parallel data streams or channels, one for each sub-carrier.
In telecommunications, direct-sequence spread spectrum (DSSS) is a modulation technique. As with other spread spectrum technologies, the transmitted signal takes up more bandwidth than the information signal that is being modulated.