ECI is a symbology-independent extension of the Global Label Identifier (GLI) system in the PDF417 barcode.
ECI allows usually unsupported national character sets such as Arabic, Greek, or Japanese to be used in barcode symbols. In theory, a barcode symbol could use several character sets by embedding several ECI codes.
As the ECI information is not intended to be part of the bar code "data," it should be transparent when the symbol is scanned. When encoding a symbol, ECI is a switch, or tick-box to be checked, followed by a symbology-dependent ECI selection. The ECI information will be encoded in a symbology-specific codeword that the decoder will recognize and interpret accordingly.
In Basic Channel Mode, the ECI control information is not transmitted from the reader to the host system. In Extended Channel Mode, both the ECI control information and the data are transmitted to the host system.