STM-1

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. Beyond this we have wavelength-division multiplexing (WDM) commonly used in submarine cabling.[1][2]

Frame structure

The STM-1 frame is the basic transmission format for SDH (Synchronous Digital Hierarchy). A 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 64kbit/s channel.[3]

TOH: Transport Overhead (RSOH + AU4P + MSOH)

VC4: Virtual Container-4 payload (POH + VC-4 Data)

Frame characteristics

The STM-1 base frame is structured with the following characteristics:

RSOH (regenerator section overhead)

The Regenerator Section OverHead uses the first three rows & nine columns in the STM-1 frame

MSOH (multiplex section overhead)

X = Bytes reserved for national use.

The Multiplex Section OverHead uses the 5th through 9th rows, and first 9 columns in the STM-1 frame.

References

  1. Chapter 8 Voice & data communications handbook By Regis J. Bates, Donald W. Gregory
  2. Table 2 Basic SONET Levels The Internet encyclopedia, Volume 1 By Hossein Bidgoli
  3. 3.3 Basic principles of SDH Networks: internet, telephony, multimedia : convergences and complementarities By Daniel Hardy, Guy Malléus, Jean-Noël Méreur
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