In telecommunications, a transverse redundancy check (TRC) or vertical redundancy check is a redundancy check for synchronized parallel bit

Bit

A bit is the basic unit of information in computing and telecommunications; it is the amount of information stored by a digital device or other physical system that exists in one of two possible distinct states...

s applied once per bit time, across the bit streams. This requires additional parallel channels for the check bit or bits.

The term usually applies to a single parity bit

Parity bit

A parity bit is a bit that is added to ensure that the number of bits with the value one in a set of bits is even or odd. Parity bits are used as the simplest form of error detecting code....

, although it could also be used to refer to a larger Hamming code

Hamming code

In telecommunication, Hamming codes are a family of linear error-correcting codes that generalize the Hamming-code invented by Richard Hamming in 1950. Hamming codes can detect up to two and correct up to one bit errors. By contrast, the simple parity code cannot correct errors, and can detect only...

.

The adjective "transverse" is most often used when it is used in combination with additional error control coding, such as a longitudinal redundancy check

Longitudinal redundancy check

In telecommunication, a longitudinal redundancy check or horizontal redundancy check is a form of redundancy check that is applied independently to each of a parallel group of bit streams...

. Although parity alone can only detect and not correct errors, it can be part of a system for correcting errors.

An example of a TRC is the parity written to the 9th track of a 9 track tape.