To Carry signals, using Virtual Containers (VC: Virtual Container). In the VC that are sections overload (POH: Path Overhead), which are used by pointers. The transport of containers on STM 1 STM 16 done by TDM. The couple VC-pointer, called AU (Administrative Unit) can therefore to carry both synchronous signals. Depending on the speed, the units are two levels Possible AU3 and AU4. Containers