DFS

4.5.5.3 DFS

Radio regulations might require RLANs operating in the 5 GHz band to implement a mechanism to avoid
co-channel operation with radar systems and to provide uniform utilization of available channels. The DFS
service is used to satisfy these regulatory requirements.
The DFS service provides for the following:
— Association of STAs with an AP in a BSS based on the STAs’ supported channels.
— Quieting the current channel so it can be tested for the presence of radar with less interference from
other STAs.
— Testing channels for radar before using a channel and while operating in a channel.
— Discontinuing operations after detecting radar in the current channel to avoid interference with
radar.
— Detecting radar in the current and other channels based on regulatory requirements.
— Requesting and reporting of measurements in the current and other channels.
— Selecting and advertising a new channel to assist the migration of a BSS after radar is detected.
4.5.6 Traffic differentiation and QoS support
IEEE Std 802.11 uses a shared medium and provides differentiated control of access to the medium to
handle data transfers with QoS requirements. The QoS facility (per MSDU traffic category and
TSPEC negotiation) allows an IEEE 802.11 LAN to become part of a larger network providing end-to-end
QoS delivery or to function as an independent network providing transport on a per-link basis with specified
QoS commitments. The specifications regarding the integration and operability of the QoS facility in
IEEE 802.11 specification with any other end-to-end QoS delivery mechanism like Resource Reservation
Protocol (RSVP) are beyond the scope of this standard.
4.5.7 Support for higher layer timer synchronization
Some applications, e.g., the transport and rendering of audio or video streams, require synchronized timers
shared among different STAs. Greater accuracy (in terms of jitter bounds) or finer timer granularity than that
provided by a BSS timing synchronization function (TSF) may be an additional requirement. In support of
such applications, this standard defines a MAC service that enables layers above the MAC to accurately
synchronize application-dependent timers shared among STAs. The service is usable by more than one
application at a time.