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

OTH – Optical 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