The subscriber unit must be synchronized to the nearby base
station as it monitors the BCH.
By receiving FCCH, BCCH messages, the subscriber would be
locked on to the system and the appropriate BCH.
User dials the intended digit combination and presses ―Send‖ on
The mobile transmits a burst of RACH data.
The base station then responds with an AGCH message on CCCH
which assigns the mobile unit a channel for SDCCH connection.
Once tuned to SDCCH, the subscriber will wait for SACCH frame
to be transmitted which informs the mobile of any required timing
advance and transmitter power command. The base station is able
to determine the timing advance and the signal level from mobiles
earlier RACH transmission.
Upon receiving and processing the timing advance info in the
SACCH, the subscriber is now able to transmit normal burst
messages as required for speech traffic.
The SDCCH sends message between the mobile unit and the base
station, taking care of authentication& user validation.
PSTN connects the dialed party to the MSC and the MSC switches
the speech path to the serving base station. Data is transferred on
both the forward and reverse links. The calls is successfully
underway and SDCCH is vacated.