Method and system for calculating and verifying the integrity of data in a data transmission system

A system for calculating and verifying the integrity of data in a data communication system comprising a base station and one or more tags, the system comprising:

• transmitting means for transmitting select instructions from the base station to said one or more tags, the select instruction containing a data field which matches a portion of an identity or other data field in one or more of the tags;
• transmitting means for transmitting from a selected tag or stations a truncated reply containing identity data or other data of the tag but omitting the portion transmitted by the base station;
• and
• calculating means for calculating in the base station a check sum or CRC from the data field originally sent and the truncated reply data received;
• and
• a comparator for comparing the calculated check sum or CRC with the check sum or CRC sent by the tag.

A method of calculating and verifying the integrity of data in a data communication system comprising a base station and one or more remote stations, the method including:

• transmitting a select instruction from the base station to said one or more remote stations, the select instruction containing a data field which matches a portion of an identity or other data field in one or more of the remote stations;
• communicating from a selected remote station or stations a truncated reply containing identity data or other data of the remote station but omitting the portion transmitted by the base station;
• and
• calculating in the base station a check sum or CRC from the data the truncated reply data received and comparing the calculated check sum or CRC with the check sum or CRC sent by the remote station.

A method of calculating and verifying the integrity of data in a data communication system comprising one or more base stations and one or more remote stations, the method including:

• transmitting a select instruction from the remote station to said one or more remote base stations, the select instruction containing a data field which matches a portion of an identity or other data field in one or more of the remote base stations;
• transmitting from a selected bases station or stations a truncated reply containing identity data or other data of the base station but omitting the portion transmitted by the remote station;
• calculating in the remote station a check sum or CRC from the data the truncated reply data received;
• and
• comparing the calculated check sum or CRC with the check sum or CRC sent by the remote station.

A reader or interrogator for use in a system with one or more remote stations, the reader including:

• a transmitter arranged to transmit one or more select instructions to said one or more remote stations, the select instruction or instructions containing a data field which matches a portion of an identity or other data field in one or more of the remote stations;
• a receiver arranged to receive a truncated reply containing identity data or other data of the remote station but omitting the portion transmitted by the reader or interrogator;
• calculating means for calculating a check sum or CRC from the field originally sent and the truncated reply data received, or calculated from the check sum or CRC from the truncated data alone;
• and
• a comparator for comparing the calculated check sum or CRC with the check sum or CRC sent by the remote station.