Annex A. WLAN(802.11b/DSSS) Specifications
OfficeServ 500 Wireless LAN Service Manual/Ed.00
Annex A-4
© SAMSUNG Electronics Co., Ltd.
3.2 MAC
Layer
MAC layer supports both an ad-hoc network and a client/server infrastructure
network. CSMA/CA are base on distributed coordination function(DCF) and uses
random back off algorithm to prevent the layer from collide with other media.
Point coordination function(PCF) is optional and is used for adjusting the priority of
media.
PCF enables access point to operate as point coordinator in basic service coverage
areas and clients get priority. PCF is suitable for time-bounded services such as voice
application.
The details of CSMA/CA are as follows.
Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA)
Standardized 802.11 uses CSMA to implement peer to peer as a basic connection way
because CSMA expands the connection way of Ethernet(IEEE802.3) to wireless
network.
It is not easy to detect collision in CSMA unlike cable media. Since there is a station
that fails to detect carriers within a section due to hidden terminals, A CSMA/CA
with Ack way reserving transmittance time using RTS/CTS frame and returning Ack
frame for checking transmittance is used.
Since CSMA is based on Distribution Coordination Function(DCF), the time of
gap(IFS) for sending CTS and Ack frames that operators do not want to disconnect to
CSMA is supposed to be shorter than that of IFS for sending RTS or data frames.
In addition, associated IFS should be used when an error occurs due to Point
Coordination Function PCF) and interference in Access Point AP).
