What is OTM / OADM / ROADM / FOADM ?

OTN - Optical Transmission Network Node Types

There are 3 types of the Optical Transmission Network Node as the following details

1. OTM - Optical Terminal Multiplexer

The terminal multiplexer contains the following functions:

- It can be support for both of the wavelength converting transponder for each wavelength signal it will carry and to receive the input optical signal.- To convert that signal into the electrical domain.- To re-transmit the signal 

2. OADM - Optical add-drop multiplexer

"Optical add-drop multiplexer (OADM)" is a device used in WDM systems (wavelength-division multiplexing). "Add" and "drop" is a capability device to add one or more new wavelength channels to an existing multi-wavelength WDM signal or to drop (remove) one or more channels, passing those signals to "another network path". 

There are 2 types of OADM node as the following details.

2.1 ROADM - Re-configurable optical add-drop multiplexer 

Before the development of device as a ROADM, we need to convert the optical signals to electrical signals and rout those signals by using conventional electronic switches then convert back again to optical signals. But now ROADM is no need to convert like before, the configuration can be done as required without affecting traffic. ROADM also allows for remote configuration / reconfiguration via the NMS (Network Management System).

The ROADM is a dynamic wavelength arrangement scheme, allows for dynamic wavelength arrangement scheme using a Wavelength Selective Switch (WSS). The WSS provides an 8-dimensional cross-connect and enables quick service start-up, remote cross-connect and WDM mesh networking. The ROADM scheme also allows inputting / outputting a single wavelength or wavelength group via the fixed port.

2.2 FOADM - Fixed Optical Add/Drop Multiplexer

The FOADM is a traditional wavelength arrangement scheme that can only input / output a single wavelength via the fixed port.

The distinctness of ROADM is flexible for configuration but the FOADM is Fixed.

3. OA - Optical  Amplifier

Incase of the transmit signals over long distances (>100 km), it is necessary to compensate for attenuation losses within the fiber. The amplifier could be used as a splitter the carrying signal in fiber iptic.

Description for the connection between each types of the particular node: