STM-1

Synchronous Transport Module (Synchronous Transport Module).

The STM - 1 (Synchronous Transport Module, level - 1) is the transmission standard of the SDH ITU-T fiber optic network. It has a bit rate of 155.52 Mbit/s. The highest levels increase 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).

It is the Basic Transmission Unit of the Synchronous Digital Hierarchy (SDH), corresponding to the first basic level.

It is a frame of 2430 bytes, distributed in 9 rows and 270 columns. The first nine columns contain only management information and are distributed in three fields:

STM-1 frame.

• Regeneration section Tara (RSOH), rows 1-3 [27 bytes]
• Pointer of the administrative unit, row 4 [9 bytes]
• Multiplexation section Tara (MSOH), rows 5-9 [45 bytes]

The remaining columns (10-270) contain payload. Typically, this is one virtual tier-4 container (VC-4) or three virtual tier-3 containers (VC-3). However, in Europe only VC-4 are used.

A VC-4 virtual container and administrative unit pointer make up a level 4 administrative unit (AU-4). Therefore, an STM-1 frame is generated by adding the corresponding RSOH and MSOH overheads to an AU-4.

The transmission is done bit by bit in the direction from left to right and from top to bottom. The frame is transmitted at the rate of 8000 times per second (each frame is transmitted in 125 μs,= 1/(8000 Hz)). Therefore the binary regime is equal to:

8000× × 270orctetors× × 8bits× × 9filas=155520{displaystyle 8000times {270octetos}times {8bits}times {9filas}=155520} kbit/s =155,52{displaystyle = 155,52} Mbit/s

Multiples of this transmission ratio (8000) give rise to the STM-4, STM-16, STM-64 and STM-256 links described in the SDH standard.

Transmission can be performed via electrical or optical interface.

To Complement the latter:

STM-1 = 8000 x (270 octets x 9 rows x 8 bits) = 155 Mbit/s.

STM-4 = 4 x 8000 x (270 octets x 9 rows x 8 bits) = 622 Mbit/s.

STM-16 = 16 x 8000 x (270 octets x 9 rows x 8 bits) = 2.5 Gbit/s.

STM-64 = 64 x 8000 x (270 octets x 9 rows x 8 bits) = 10 Gbit/s.

STM-256 = 256 x 8000 x (270 octets x 9 rows x 8 bits) = 40 Gbit/s.