The Mapping Scheme is the basis of the SDH. It represents all functions needed to introduce a PDH signal into an SDH Network.
SDH transmission is based on standard functional entities, used to transport a characteristic
information through a connection between two Termination Points in the network.
The SDH entities are:
* C-n = Container of order n : this is the information structure carrying a synchronous
payload.
* VC-n = Virtual Container of order n: this is the information structure formed by C-n+ Path
Over Head (POH)
* TU-n = Tributary Unit of order n: information structure formed by VC-n + Pointer
* AU-4 = Administrative Unit of order 4: information structure which provides for adaptation
(synchronization) between the Virtual Containers (VC-n) and the multiplexing plane (=
STM-N); it is formed by VC-4 + Pointer
* POINTER = Indicator of off-set for VC-n ( it indicates the start position of VC-n inside the
payload)
* TUG/AUG = Tributary Unit Group / Administrative Unit Group = a set of n x TU / n x AU
* TU12 is identified by (k,l,m) with: k= TUG3# (1…3); l=TUG2# (1…7); m=TU12# (1…3)