AU-N

administrative unit - level N

A managed entity within the SDH structure that is the top of the STM-1 configuration hierarchy.

AU-3 has the payload pointer for each payload envelope that is consolidated with the respective payload in one unit. An STM-1 frame has three payload envelopes; therefore, the frame has three AU-3 units. AU-4 applies to the entire STM-1 payload. The AU-4 structure is the only AU in an STM-1 frame.