3 Types of optical networks, their architectures and basic parameters (OTH, FFTx)
3.3 Optical Transport Hierarchy

OTHOptical Transport Hierarchy. Signals of optical hierarchy are known as OTM (Optical Transport Module). The simplest option (zero level) assumes no wavelength multiplex. Optical transport modules are denoted as OTM-n.m, where n is the number of channels (operating wavelengths) and m expresses the type of signal. Different basic rates can be multiplied; potential combinations refer to OTM-n.123 (2.5; 10; 40 Gbps).

Optical Transport Hierarchy OTH –transport modules without multiplexing

Hierarchic level

Transmission rate [Mbps]

It can transmit STM-N

OTM-0.1

2488.32

STM-16

OTM-0.2

9953.28

STM-64

OTM-0.3

39813.12

STM-256

An STM is Synchronous Transport Module, a basic transport unit in SDH (Synchronous Digital Hierarchy). N stands for multiplication of the basic unit’s capacity.

Optical transport modules with wavelength multiplexing

Hierarchic level

Transmission rate [Mbps]

It can transmit

OTM-n.1

n x 2488.32

n x STM-16

OTM-n.2

n x 9953.28

n x STM-64

OTM-n.3

n x 39813.12

n x STM-256