Basics of STM & SDH

STM

Basically refers as Synchronous Transport Module. Sometimes we hear it or tell it as STM card, used at Router end for connectivity with ISP.

STM-1: 

STM1 is a synchronous digital hierarchy (SDH) is standardized multiplexing protocols that transfer multiple digital bit streams over optical fiber using lasers or light emitting diodes (LEDs).

The STM -1 is the basic transmission format for SDH. Module level 1 is the SDH ITU-T fiber optic network transmission standard. It is one type of Electrical optical Converter [OC 3] . 

• It has the transmission bit rate of 155.52 Mbits.
• STM-1 operates in 1.31 micrometer lasers for 40km over single mode and 1.55 for longer.

first stm-1 generator

STM-1 card used for router

The STM-1E card has three card-level LED indicators. 

The red FAIL LED indicates a hardware problem on the STM-1E card; the green ACTV LED indicates that the STM-1E card is active and ready to carry traffic. The yellow SF LED indicates a problem receiving incoming data (loss of signal [LOS], loss of frame [LOF], or high bit error rate [BER]) on one or more of the STM-1E ports on the card.

STM-1 Frame:

The basic STM-1 carrier frame is made of 8 overheads, 4 pointers and a space for the payload. The overheads are the Regeneration Section Overhead (RSOH), linked with the regenerators, and the Multiplex Section Overhead (MSOH), associated with the multiplexers.

Regenerator Section Overhead (RSOH):

The Regenerator Section Overhead uses the initial 3 rows and 9 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 related to other data packets.

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

Like wise STM 1 there are other variants of SDH transmission rates as STM-4, STM-16 and STM-64. Sometimes combinedly we call it as STM-1/4/16 SDH Multiplexer.

Below are the transmission bit rate,

STM-4 = 622.080 Mbit/s

STM-16 = 2,488.320 Mbit/s or approx. 2.5 Gbit/s

STM-64 = 9,953.280 Mbit/s or we can say approx. 10 Gbit/s

SDH 

Synchronous Digital Hierarchy

Synchronous Optical Networking [SONET] or Synchronous Digital Hierarchy are a standard for data transmission or we can say, it is a standardized multiplexing protocols that transfer multiple digital bit streams over optical fiber using lasers or Light Emitting Diodes.

• It is a transport Protocol.
• The STM-1 frame is basic transmission format for SDH. 

The STM-1 frame is transmitted in exactly 125ms therefore 8000 frames per second on Fiber Optic ckt.

PDH

Plesiochronous digital hierarchy or PDH was used earlier in network for data transmission through microwave or fibre optical cables. Later PDH has been replaced by SDH.

-DR