Process for determining the origin of bit errors in a data stream transmitted from a data source to a data receiver

In a system having

• a data source, providing a data stream, the data stream including
• a plurality of data cells, each of the data cells having a cell head and a useful field,
• at least one intermediate transmission path, providing a transmission path for the data stream, and having a device for correcting bit errors in the cell head,
• a scrambler, scrambling the data stream in accordance with a specified instruction of a predetermined period length,
• a first transmission path lying adjacent to a receiver and a second transmission path lying distant from the receiver, each transmission path providing a transmission path for the scrambled data stream, and
• a descrambler, descrambling the scrambled data stream in accordance with an instruction corresponding to the specified instruction of a predetermined period length,
• a method for determining the origin of bit errors in the descrambled data stream comprising steps of:
• a) injecting test data into test cells;
• b) checking the cell heads for bit errors;
• c) evaluating bit errors contained in the descrambled data stream;
• d) deriving a bit error function from received test data based on the evaluation of bit errors of step (c);
• e) evaluating the bit error function section by section, based on the predetermined period length;
• f) determining a period length of the bit error function based on the section by section evaluation of the bit error function of step (e);
• g) comparing the period length of the bit error function determined in step (f) with the predetermined period length;
• h) determining the origin of the error to lie in the first transmission path if the period length of the bit error function determined is equal to the predetermined period length and if an error is detected in the cell head, determining the origin of the error to lie in the second transmission path if the period length of the bit error function determined is equal to the predetermined period length and an error is not detected in the cell head, and determining the origin of the error to lie in the intermediate transmission path if the period length of the bit error function determined is not equal to the predetermined period length.