3 in 4 encoding
3-in-4 coding is a character-oriented coding method.
The 3-in-4 method can be used to transmit user data with any structure. The user data is encoded in such a way that only characters are generated that are not reserved for control messages. A disadvantage is the very large overhead of 33% ( transmission time, data volume), since the user data are each converted in blocks of 3 bytes into blocks of 4 bytes of the channel signal. 3-in-4 coding is used, for example, for transparent transmission of telesoftware in T-Online.