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Station services support transport of MSDUs between stations within the same BSS. They
are present in every 802.11 station. The station service subset is
a)
Authentication
b)
Deauthentication
c)
Privacy
d)
MSDU delivery
Distribution system services are provided by the DS and they enable the MAC to transport
MSDUs between BSSs within an ESS. The DSS service subset is
a)
Association
b)
Disassociation
c)
Distribution
d)
Integration
e)
Reassociation
Distribution delivers MSDUs within the DS. It is the job of the DS to deliver the message in
such a way that it arrives at the appropriate DS destination for the intended recipient. The
necessary information for the message distribution is provided by the three association
related services.
Integration enables delivery of MSDUs between the DS and an existing wired network. The
message is delivered via the portal and the integration service is responsible for
accomplishing whatever is needed to deliver a message from the DS to the wired LAN
media.
The different association services support different categories of mobility. The basic
association service establishes association between a station and an access point. The
information is needed for the message delivery via DS. At any time, a station may be
associated with no more than one access point, while an access point may be associated
with many stations at a time. Association is always initiated by the mobile station.
Reassociation enables the transfer of an existing association from one access point to
another within an ESS. Reassociation also enables changing of attributes of an established
association while a station remains associated with the same access point. The existing
connections must be maintained during the reassociation.
Disassociation voids an existing association. It can be invoked by either party of the
association and cannot be refused by the other party.
Authentication is used when stations identify each other. Since wireless media is not
bounded like wired 802.11, it supports several authentication processes although it does not
mandate the use of any particular authentication service. 802.11 provides link level
authentication between stations. It does not provide end-to-end or user-to-user
authentication. 802.11 authentication is simply used to bring the wireless link up to the
assumed physical standards of a wired link. 802.11 also supports shared key authentication
with the WEP (Wired Equivalent Privacy) option. Authentication is void by Deauthentication.
Privacy is closely related to authentication. This service is used to prevent the contents of
messages from being read by anybody else than the intended recipient.
2.1.5 WLAN Summary
The Nokia D211 supports the IEEE 802.11b standard that is the industry de facto standard.
The maximum data rate is 11 Mbit/s. The Nokia D211 operates on the 2.4 GHz ISM
frequency band.
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