Several frame structures have been defined for Asymmetric Digital Subscriber Line (ADSL). In general, an ADSL frame consists of an ADSL superframe in which the frame fine structure of the individual DMT symbols is represented.
The superframe consists of a total of 68 transmission frames for the user and control information and a synchronization frame.
The user data frames are based on a frequency of 4 kHz (250 µs). The individual user data frames consist of seven logical channels, of which four to seven can be used for user data transmission in the downstream direction and a maximum of three for transmission in the upstream direction. In addition, the data frames contain control bytes and fields for forward error correction (FEC).