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