1. Synchronous Digital Hierarchy

2. SDH
On the right of the figure we can see the tributaries that can be transported.
First these are mapped into their C-n container, then an overhead is added and they become VC-n virtual containers.
Next they are aligned when the pointer bytes are associated with them, giving rise to the tributary units and administrative units, TU-n and AU-n respectively.

3. Frame

4. Frame STM-1

5. STM1

6. SOH = MSOH and RSOH
RSOH (Regeneration Section Overhead) -bytes of the STM-N frame with which they detect and give warnings of errors and alarms.
MSOH (Multiplex Section Overhead) - bytes let the network be monitored and give warnings about errors

7. STM1-STM2

8. Byte Byte Multiplexing

9. C4

10. Containers (C-4)
Synchronous transport units were designed to transport plesiochronous signals in SDH networks - these are called containers.

11. VC4

12. Path Overhead (POH)
A series of bytes is added to each container (C-4) and these carry information that enables the system to manage this container. These bytes are known as the overhead. Together, the overhead bytes and the container is known as the virtual container
This overhead provides information about the path and lets us monitor different parameters

13. VC4

14. AU4

15. AU-4
The SDH system does not define optimized containers for transporting tributary signals whose bit rate is higher than 140 Mbit/s. This means that a signal with a transmission rate of higher than 140 Mbit/s cannot be packed in any predefined container. So, how can we transport such a signal?
The concatenation mechanism provides a solution to this problem. It consists of combining the number of virtual containers needed to form a virtual container whose capacity is greater than or equal to the capacity required.

16. C3

17. VC3

18. Tributary Units - TU
Together, the pointer and the VC-n make up the tributary unit (TU).
The TU-3 corresponds to the VC-3

19. TUG3

20. Forming STM-1

21. E1 to SDH

22. C12

23. C12

24. Multiframe VC12

25. TU-12 - TUG-2

26. TUG-2 - TUG-3

27. TUG-3 - TUG-4

28. C4 – STM1

29. C3 – STM1

30. C2 – STM1