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Frame Structure of SDH

The Synchronous Digital Hierarchy (SDH) frame structure is organized into a set of standardized frames at different levels of the hierarchy. The basic building block is known as the STM-1 (Synchronous Transport Module level 1) frame. Here's an overview:


1. STM-1 Frame:

   - Frame Duration: 125 microseconds

   - Payload Capacity: 9 rows by 270 columns of bytes

   - Payload Rate: 155.52 Mbps


2. Higher-Level Frames:

   - Higher levels (STM-4, STM-16, STM-64, etc.) are formed by multiplexing lower-level frames.

   - Each higher level represents an increased bit rate and capacity.


3. Virtual Containers (VCs):

   - Within the STM-1 frame, there are Virtual Containers (VCs) that carry different types of payloads.

   - VC-12: Carries 2 Mbps (E1) signals.

   - VC-3: Carries 34 Mbps (DS3/T3) signals.

   - VC-4: Carries 140 Mbps signals.


4. Administrative Units:

   - AU-3 (Administrative Unit level 3): Corresponds to the VC-4, which is the basic building block of higher-level STM-N frames.


5. Synchronization:

   - The frame structure is designed to maintain synchronization, ensuring that all network elements are synchronized to a common clock.


6. Overhead:

   - Frames include overhead bytes used for management and control purposes.

   - Section Overhead (SOH): Used for section monitoring.

   - Line Overhead (LOH): Used for line monitoring.

   - Path Overhead (POH): Used for path monitoring.


7. Multiplexing Structure:

   - The multiplexing structure allows for flexible aggregation of different lower-level signals into higher-level signals.


8. Concatenation:

   - Concatenation allows for the grouping of multiple lower-level signals to create higher-capacity signals.


9. Regenerator Section:

   - The basic transmission span between regenerators is called the Regenerator Section.


10. MSOH (Multiplex Section Overhead):

   - Additional overhead for managing multiplexed signals.


Understanding the SDH frame structure is crucial for the efficient transport of different types of data across telecommunications networks. The standardized frame structure enables interoperability between different vendors' equipment within the SDH network.

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