Point Coordination Function (Pcf); Ad-Hoc Networks - Black Box LW0050A Manual

APPENDIX E: IEEE 802.11 Technical Tutorial
E.12 Point Coordination Function (PCF)
Beyond the basic Distributed Coordination Function, there is an optional Point
Coordination Function, which may be used to implement time-bounded services,
like voice or video transmission. This Point Coordination Function makes use of
the higher priority that the Access Point may gain by the use of a smaller Inter-
Frame Space (PIFS).
By using this higher-priority access, the Access Point issues polling requests to the
stations for data transmission, thus controlling medium access. To still enable
regular stations to access the medium, there is a provision that the Access Point
must leave enough time for Distributed Access in between the PCF.
E.13 Ad-hoc Networks
In certain circumstances, the users may wish to build up wireless LAN networks
without an infrastructure (more specifically without an Access Point). This may
include file transfer between two notebook users, coworkers meeting outside the
office, etc.
The 802.11 Standard addresses this need by the definition of an "ad-hoc" mode of
operation. In this case, there is no Access Point and part of its functionality is
performed by the end-user stations (such as Beacon Generation, synchronization,
etc.). Other Access Point functions are not supported (such as frame-relaying
between two stations not in range, or Power Saving).
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