SDH is the infrastructure for thetelecommunication network sof the 21 stcentury, providing broadband and intelligent services.
For the details, SDH structure willbe explained:
SDH Multiplexing Terminology
1.1 Container (C-n)
A container is the information structure with standardized transmission capacity that carries existingPDH or B-ISDN services. Besides information bits, it contains justification bits for synchronizing aPDH signal to the SDH clock frequency and other stuffing bits.
1.2 Virtual Container (VC-n)
A VC is the information structure that supports the Path Layer Connection. It consists of aninformation ‘payload’ of the supported service information bits and POH (path overhead) for OAMPmanagement of the VC path. VC-11, VC-12 and VC-2 are called a Lower Order VCs (LOVC), andtheir payload is C-11, C-12 and C-2 respectively. VC-3 and VC-4 are called Higher Order VCsHOVC) and their payload is C-3 and C-4 respectively or multiple lower order VCs. The process of bitby bit placement of the service into the VC is called ‘mapping’.
1.3 Tributary Unit (TU-n)
A TU is an information structure that provides adaptation between a lower order VC and a higherorder VC. It consists of a lower order VC and a TU pointer. The pointer is an address that indicatesthe offset between the start of the LOVC frame and the start of the HOVC frame. This process iscalled ‘aligning,’
1.4 Tributary Unit Group (TUG-n)
A TUG combines one or multiple homogeneous TUs (all of the same type) into a single unit. A TUG-2 consists of identical TU-1s (all TU11 or all TU12) or a single TU-2. A TUG-3 consists of multipleTUG-2s or a single TU-3.
1.5 Administrative Unit (AU-n)
An AU is an information structure that provides adaptation between a payload (HOVC) and an STM-N. It consists of a HOVC and an AU pointer address that indicates the offset between the start of theHOVC frame and the start of the STM-N frame.An AU-4 consists of a VC-4 and AU pointer and an AU-3 consists of a VC-3 and AU pointer.
1.6 Administrative Unit Group (AUG)
An AUG contains a single AU-4 or three homogeneous AU-3s. If three AU-3s, they are combinedusing byte interleaved multiplexing.
1.7 Synchronous Transport Module (STM-N)
An STM is the information structure that supports Section Layer Connection and consists ofinformation payload and SOH (section overhead) for management of the section.A basic STM is defined at 155.52Mb/s and the bit rate of STM-N is N times multiple of 155.52Mb/s.If N>1, the multiple AUs are combined using byte interleaved multiplexing.