Wireless-LAN-Architecture

WirelessLAN Stations

Allcomponents that can connect into a wireless medium in a network are referredto as stations. All stations are equipped with wireless network interface cards(WNICs). Wireless stations fall into one of two categories: access points andclients.

• Access points

Access points (APs) are base stations for the wirelessnetwork.They transmit and receive radio frequencies for wireless enableddevices to communicate with.

• Clients

Wireless clients can be mobile devices such as laptops,personal digital assistants, IP phones, or fixed devicessuch as desktops and workstations that are equippedwith a wireless network interface.

Basicservice set

Thebasic service set (BSS) is a set of all stations that cancommunicate with each other. There are two types of BSS: independentBSS and infrastructure BSS. Every BSS has an identification (ID) calledthe BSSID, which is the MAC address of the accesspoint servicing the BSS.

• Independent basic service set

An independent BSS is an ad-hoc network thatcontains no access points, which means they can not connect to anyother basic service set.

• Infrastructure basic service set

An infrastructure BSS can communicate with other stationsnot inthe same basic service set by communicating through access points.

Extendedservice set

Anextended service set (ESS) is a set of connected BSSes. Accesspoints in an ESS are connected by a distribution system. Each ESS hasan ID called the SSID which is a 32-byte (maximum) character string.For example, "linksys" is the default SSID for Linksys routers.

Distributionsystem

Adistribution system connects access points in an extended service set.

Typesof wireless LANs

Peer-to-peer

Peer-to-Peer or ad-hoc wirelessLAN

A peer-to-peer(P2P) allows wireless devices to directly communicate with each other.Wireless devices within range of each other can discover andcommunicate directly without involving central access points. Thismethod is typically used by two computers so that they can connect toeach other to form a network.

If asignal strength meter is used in this situation, it may notread the strength accurately and can be misleading, because itregisters the strength of the strongest signal, which may be theclosest computer.

802.11specs define the physical layer (PHY) and MAC (Media AccessControl) layers. However, unlike most other IEEE specs, 802.11 includesthree alternative PHY standards: diffuse infrared operating at 1 Mbit/sin; frequency-hopping spread spectrum operating at 1 Mbit/s or 2Mbit/s; and direct-sequence spread spectrum operating at 1 Mbit/s or 2Mbit/s. A single 802.11 MAC standard is based on CSMA/CA (Carrier SenseMultiple Access with Collision Avoidance). The 802.11 specificationincludes provisions designed to minimize collisions. Because two mobileunits may both be in range of a common access point, but not in rangeof each other. The 802.11 has two basic modes of operation: Ad hoc modeenables peer-to-peer transmission between mobile units. Infrastructuremode in which mobile units communicate through an access point thatserves as a bridge to a wired network infrastructure is the more commonwireless LAN application the one being covered. Since wirelesscommunication uses a more open medium for communication in comparisonto wired LANs, the 802.11 designers also included a shared-keyencryption mechanism, called wired equivalent privacy (WEP), or Wi-FiProtected Access, (WPA, WPA2) to secure wireless computer networks.

Bridge

Abridge can be used to connect networks, typically of different types. Awireless Ethernetbridge allows the connection of devices on a wired Ethernet network toa wireless network. The bridge acts as the connection point to theWireless LAN.

Courtesy of Wikipedia. All text is available under the terms of the GNUFree Documentation License. (See Copyrights for details.)