Timing synchronization function
Timing synchronization function (TSF) is specified in IEEE 802.11 wireless local area network (WLAN) standard to fulfill timing synchronization among users. A TSF keeps the timers for all stations in the same basic service set (BSS) synchronized. All stations shall maintain a local TSF timer. Each mobile host maintains a TSF timer with modulus 264 counting in increments of microseconds. The TSF is based on a 1-MHz clock and "ticks" in microseconds. On a commercial level, industry vendors assume the 802.11 TSF's synchronization to be within 25 microseconds. Timing synchronization is achieved by stations periodically exchanging timing information through beacon frames. In (intra) BSS, the AP sends the TSF information in the beacons. In Independent Basic Service Set (IBSS, ad-hoc), each station competes to send the beacon. Each station maintains a TSF timer counting in increments of microseconds (μs). Stations adopt a received timing if it is later than the station’s own TSF timer. IBSS operation overview All stations in the IBSS adopt a common value, aBeaconPeriod, that defines the length of beacon intervals or periods. This value, established by the station that initiates the IBSS, defines a series of target beacon transmission times (TBTTs) exactly aBeaconPeriod time units apart.