In digital data transmission, a system employing either forward error correction (FEC) or automatic repeat-request (ARQ) techniques such that most transmission errors are automatically removed from the data unit prior to delivery to the destination facility.

A code in which each telegraph or data signal conforms to specific rules of construction, so that departures from this construction in the received signal can generally be detected automatically.
Note: Error-detecting codes require more signal elements than are necessary to convey the basic information.

A system employing an error-detecting code and so arranged that any signal detected as being in error is either deleted from the data delivered to the data sink, in some cases with an indication that such deletion has taken place, or delivered to the data sink together with an indication that the signal is in error.

Synonym ARQ.

A 1-yysecond interval in which no errored blocks are received.
Note: In general, measurement is over time and is stated as a percentage, i.e., % EFS. [T1.514-1995]

1. A 1-yysecond period with one or more errored blocks.
2. A 1-second interval with one or more bit errors.
Note 1: Severely errored seconds (SES) are defined as a subset of ES.
Note 2: A period of loss of signal is considered as a period of errored blocks. [T1.514-1995]

A specified period of time, during which bits are transferred from a source to a destination, that contains at least one bit in error. Examples of an errored unit of time are an errored second (ES), and a severely errored second. [After T1.507-1996]

1. End System,
2. Expert System,
3. Errored-Second.

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