STM-1
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The STM-1 (Synchronous Transport Module level-1) is the SDH ITU-T fiber optic network transmission standard. It has a bit rate of 155.52 Mbit/s. Higher levels go up by a factor of 4 at a time: the other currently supported levels are STM-4, STM-16, STM-64 and STM-256. Above STM-256 wavelength-division multiplexing (WDM) is commonly used in submarine cabling.[1][2]
The STM-1 frame is on the basic transmission format for SDH (Synchronous Digital Hierarchy). An STM-1 frame has a byte-oriented structure with 9 rows and 270 columns of bytes, for a total of 2,430 bytes (9 rows * 270 columns = 2430 bytes). Each byte corresponds to a 64 kbit/s channel.[3]
TOH: Transport Overhead (RSOH + AU4P + MSOH)
- MSOH: Multiplex Section Overhead
- RSOH: Regeneration Section Overhead
- AU4P: AU-4 Pointers
VC4: Virtual Container-4 payload (POH + VC-4 Data)
- POH: Path Overhead
Frame characteristic
The STM-1 base frame is structured with the following characteristics:
- Length: 270 column × 9 row = 2430 bytes
- Byte: 1-byte = 8 bit
- Duration (Frame repetition time): 125 μs i.e. 8000 frame/s
- Rate (Frame capacity): 2430 × 8 × 8000 = 155.52 Mbit/s
- Payload = 2349 bytes × 8 bits × 8000 frames/sec = 150.336 Mbit/s
