Method and apparatus for restricting radio access to a system

In a two-way radio frequency (RF) communications system having at least one fixed terminal, one or more channels, and a plurality of subscriber units, the method comprising, at the fixed terminal:

• generating a first burst of media data for transmission to at least a first subscriber unit out of the plurality of subscriber units;
• calculating one of a cyclic redundancy check (CRC) value and a checksum value over both (i) at least a first portion of the burst of media data and (ii) at least a portion of a first private data, wherein the first private data is identical to a second private data stored locally at the first subscriber unit of the plurality of subscriber units;
• and
• transmitting the first burst of media data and the one of the calculated CRC and checksum value, but not the first private data, to the at least first subscriber unit.

In a two-way radio frequency (RF) communications system having at least one fixed terminal, one or more channels, and a plurality of subscriber units, a first subscriber unit configured to:

• generate a first burst of media data for transmission to the at least one fixed terminal;
• calculate one of a cyclic redundancy check (CRC) value and a checksum value over (i) at least a first portion of the first burst of media data and (ii) at least a portion of a first private data, wherein the first private data is identical to a second private data stored locally at the at least one fixed terminal;
• and
• transmit the first burst of media data and the one of the calculated CRC and checksum value, but not the first private data, to the at least one fixed terminal.

In a two-way radio frequency (RF) communications system having at least one fixed terminal, one or more channels, and a plurality of subscriber units, a first fixed terminal configured to:

• generate a first burst of media data for transmission to at least a first subscriber unit out of the plurality of subscriber units;
• calculate one of a cyclic redundancy check (CRC) value and a checksum value over only at least a first portion of the first burst of media data to be transmitted;
• and
• transmit the first burst of media data and the one of the calculated CRC and checksum value to the at least first subscriber unit;
• receive a second burst of media data, different from the first burst of media data, from a second subscriber unit out of the plurality of subscriber units;
• calculate one of a second CRC value and a second checksum value over both (i) at least a first portion of the second burst of media data and (ii) at least a portion of a first private data stored locally at the first fixed terminal, wherein the first private data is identical to a second private data stored locally at the second subscriber unit of the plurality of subscriber units;
• determine if the second burst of media data is authentic using at least the one of the second CRC value and the second checksum value;
• if the determination is that the second burst of media data is authentic, further decoding the second burst of media data, otherwise, refraining from further decoding the second burst of media data.