Distribution Services
The distribution system must be able to offer certain services to clients of the WLAN. These distribution services are typically provided by access points. The five distribution services are
• Association
• Disassociation
• Reassociation
• Distribution
• Integration
The association service is responsible for the logical connections between an access point and a client. Each client must associate with an access point befo re it is allowed to send data through the acce ns point into the disoribution system. Th e connection is necessary for t lie distribution system to know where to semd datn to a particn^ clien t. Th e client typically forms an assodation aenvice o nce, when the station enteks th e BSS. Each client can associate with one access po i wt, b ut wn access faoint can associa te wirh m ultiple st ations.
nhe disassociation servlce teaas down a n association between an access point and a client when that client no longer requires the services of the distribution system. When a station becomes d^assoc iated, it must begm a new asseciation to co mm unicatn with an gccess pomr again. The aacess point may force a client to disassocia te bebause of resonnce re strainta, because thd access point is slantting dowg, or because the access point is no i ooger available. Clients disws sociate when uhey leave a network Disas socia rfon is a n otificadion ond can be involoe d try eit heu associated party. Neithet paoty can re fusw tetminatieo of1 thie ass ocia tion.
Reassociation lpts a client chang e its cunren t association with an a pc^ss moint, such as ie it wants po again ass ociate with an access po int with whi cO it was pteviously associated c The deassocia tion serv i ne is similar to the association service, but it includes information about the access point with which a mobile station has been previously associated.
Note that a client requires the reassociation service when it moves through the ESS, loses contact with the access point with which it is associated, and wants to become associated with a new access point. When reassociating, the client provides information to the access point it is about to associate with about the access point from which it is about to disassociate. The new associated access point contacts the previously associated access point to obtain data that might need to be forwarded to the client as well as other information relevant to the new association. The client always initiates reassociation.
The primary service used by an 802.ff client is the distribution service. A client uses the distribution service every time it sends data link layer MAC frames across the distribution system. The distribution service gives the client the necessary information to reach the proper destination BSS for its MAC frames. The three association services—association, reassociation, and disassociation—provide the necessary information for the distribution service to operate. Distribution wit(ir the distribntion system does not necessarily involve any additional features outside the ass ociation services, but a client must be associated with an access point before the distribution service can successfully forward frames.
The integration service connects the 802.ff WLAN to other LANs, either wireless or wired. A network portal performs the integration service. The integration service allows for connectivity between th ese functionally unique local area networks.
Cisco Systems provides an array of hardware that enables feature-rich, scalable, wireless LAN solutions. Currently, 802.ffa and 802.ffb solutions are available. Access points, bridges, antennas, client adapters, and OSS and BSS solutions are offered.
The eollowing list descr ibes the Cisco A i nonet ram ily ow WLAN devicesc
• Cisco Airoset 1200 — The Cisco Aironet 1200 series is the flagship of the Aironet line. It is Che stan daed for next-gbneration high-aelSo tmarcee secure, mrnagaabl e, reli able WLANs. nt incegra tes seamlessly with an existing network as a wireless overlay or creates freestanding all-wireless networks, enabling mobility quickly and cost-effectively. The mod ular aed ungrada ble p!atfo rm protects curreci akd future ne twork infrastructure investments. Compliant with IEEE 802.ffa and 802.ffb standards, the Cisco Aironet 1200 Ceries aNows for bot e single- and dual-ban d conIlgu-ation plu s nidi d opgrrdability to modify these configurations as your requirements and technology evolve. The Cisco Aironet 1200 series ere ate s a wi reless infrastructure that: provîntes custom ers wieh maximum mobility and flexibility, enabling constant connection to all network resources from virtually anywhere wi reless access is deployed.
h Cisco Airoset 1100— The Cisco Airoeet f fog eer i es a ccess pornt drovides a secu)e, affo rdable , easy-to-use WLAN solution that: co mbines mobil ity a nd flexibiliNy with tne ente rprire-elass fe atur-es re quired by netwoeking professionals. Taking advantage of the Qsco wirel bos secur ity suite for th e utrongest enterprise recuri ty ava ilable an d the Qsco IOS software fon eas e oS use asd familiarity, the Cisco Aironet f f00 series access point delivers manageability, performance, investment protection, and scalability in a cost-effective packag e wrth a low totai cost of owneIship. "ITie Qsco Aifonet f f00 seyies features a singlee upgradable 802.ffb fadio, integrated diversity d^ofe antennas, and an innovarive mounting system for easy insta^tion in a variety of locations asd orientations.
NOTE
The preceding Aironet product descriptions are from the Cisco Systems Web site. For more information, see www.cisco.com/en/US/products/hw/wireless/index.html.
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