Frame in SDH

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STM Frame Structure

An STM-1 frame structure consists of 9 rows and 270 columns of bytes, totalling 2,430 bytes. The byte-orientated arrangement has a bit-rate of 155.52Mb/s. The frame is transmitted at 125 µs (microseconds), resulting in 8,000 frames per second on the circuit.

The frame of STM-1 consists of payload blocks, overhead blocks and pointers. The ratio of these components can vary and depends on the initial payload that needs to be transmitted.

The last 261 columns of the frame provide the information payload, the first 9 contain the overhead and administrative pointers. The administrative pointers can contain one or more virtual containers which have the path overhead or the virtual container payload information.

An STM-1 signal is divided into two categories: the regenerator section overhead and the multiplex section overhead.

Regenerator Section Overhead (RSOH)

The Regenerator Section Overhead uses the initial three rows and nine columns of the STM-1 frame. It monitors the network sections that present on the fiber-optic cable network.

Multiplex Section Overhead (MSOH)

The Multiplex Section Overhead uses the rows 5 to 9 and the first 9 columns of the STM-1 frame. It contains the information that allows data packets to be transmitted on the same network compared to other data packets.

Both overheads provide information on the transmission system and its management function, such as failure detection, service channels and monitoring of transmission quality.

Dear friend!
A rectangular block frame with 8 bits as aunit. The frame rate is 8000 rames/s, and the frame period is 125 hs. The frame is transmitted row by row. SDH frame structure: 

That is, the first row is transmitted first and then the second row is transmitted, and the overhead area and the payload area are transmitted simultaneously.

Thanks for sharing