WDM Boards

In terms of functionality, WDM boards are categorized into the following types.

Types of WDM boards for NG WDM boards

Optical transponder board (OTU)

An OTU (Optical Transponder Unit) board converts client-side services into standard optical signals after performing mapping, convergence, and other procedures. The board also performs the reverse process.

Examples: LWF, LQG, L4G and other boards.

Figure 1 shows the positions of OTU boards in a WDM system.

Figure 1 Positions of OTU boards in a WDM system

OTN tributary boards

A OTN tributary board receives client-side services, performs O-E conversion, maps the services into ODUk containers, and lastly sends the ODUk electrical signals to cross-connect board for centralized cross-connection.

Examples: TOG, TOM, THA and other boards.

Figure 2 shows the positions of OTN tributary boards in a WDM system.

Figure 2 Positions of OTN tributary boards in a WDM system

Line boards

A line board multiplexes and maps ODUk electrical signals cross-connected from cross-connect board and performs conversion between OTUk optical signals and standard wavelengths.

Examples: ND2, NQ2, NS2 and other boards.

Figure 3 shows the positions of line boards in a WDM system.

Figure 3 Positions of line boards in a WDM system

Universal line board

A universal line board receives and processes ODUk signals, packets, or VC-4 signals from the cross-connect board. When receiving packets or VC-4 signals, the board maps the them into ODUk signals, performs multiplexing and E/O conversion, and sends out an OTUk optical signal carried over an ITU-T G.694.1-compliant DWDM wavelength. When receiving ODUk signals, the board directly performs multiplexing and E/O conversion.

Examples: HUNS3, HUNQ2, TN56NS3

Figure 4 illustrates the position of a universal line board in a WDM system.

Figure 4 Position of a universal line board in a WDM system

Packet service boards

The packet service board receives and processes the ethernet services at Layer 2. The processed services are transmitted as packets to centralized cross-connect boards for grooming. Then a universal line board or packet service board can be used to direct packet services to the WDM network for transmission.

Examples: EG16, PND2, EX2

Figure 5 shows the positions of packet service boards in a WDM system.

Figure 5 Positions of packet service boards in a WDM system

PID boards

PID boards integrate the functions of traditional optical transponder boards and multiplexer/demultiplexer boards. OTN processing and output of multiplexed optical signals are implemented on one PID board, featuring large capacity, high integration, high reliability, and flexible access of various services.

Examples: ENQ2, NPO2, NPO2E and other boards.

Figure 6 shows the positions of PID boards in a WDM system.

Figure 6 Positions of PID boards in a WDM system

Optical multiplexer/demultiplexer boards

Optical multiplexer boards multiplex multiple optical signals into one ITU-T G.694-compliant optical signal. Optical demultiplexer boards demultiplex one multiplexed optical signal into individual ITU-T G.694-compliant optical signals.

Examples: M40, D40, FIU and other boards.

Figure 7 shows the positions of optical multiplexer/demultiplexer boards in a WDM system.

Figure 7 Positions of optical multiplexer/demultiplexer boards in a WDM system

FOADM boards

Fixed optical add/drop multiplexer (FOADM) boards drop individual ITU-T G.694-compliant optical signals from a multiplexed signal and send these optical signals to associated OTU boards. In addition, FOADM boards also add and multiplex individual ITU-T G.694-compliant optical signals into one multiplexed signal.

Examples: DMR1, MB2, MR2 and other boards.

Figure 8 shows the positions of FOADM boards in a WDM system.

Figure 8 Positions of FOADM boards in a WDM system

ROADM boards

Reconfigurable optical add/drop multiplexer (ROADM) boards add/drop any single or multi-wavelength signals to/from a multiplexed signal, and route the signals to any port in any order, achieving flexible wavelength grooming in multiple directions. These boards apply to DWDM systems.

Examples: WSD9, WSM9, WSMD2 and other boards.

Figure 9 shows the position of RAODM boards in a WDM system by using the WSMD4 board as an example.

Figure 9 Positions of ROADM boards in a WDM system

Optical amplifier board

The optical amplifier board amplifies the power of the multiplexed optical signals to extend the transmission distance.

Examples: OAU1, HBA, RAU1 and other boards.

Optical amplifier boards are used to compensate for power loss caused by long haul transmission in fiber communication systems. They are classified into erbium-doped fiber amplifier (EDFA) boards and Raman boards. Figure 10 shows the positions of optical amplifier boards at an OTM site in a WDM system.

Figure 10 Positions of EDFA and Raman boards in a WDM system

OSC boards

OSC boards transmit optical supervisory information between two NEs. OSC boards provide high reliability of network monitoring because OSC boards transmit an OSC signal using a wavelength different service wavelengths.

Examples: SC1, SC2, ST2 and other boards.

Figure 11 shows the positions of OSC boards in a WDM system. In the preceding figure, the SCC board on NE1 sends the local NMS monitored data to the OSC board. Then the OSC board converts the NMS monitored data into an OSC signal and sends the signal to the SFIU/FIU board. Lastly, the SFIU/FIU board multiplexes the signal with the main channel signal onto the line for transmission. On NE2, the FIU/SFIU board extracts the OSC signal from the line and sends it to the OSC board. Then the OSC board restores the monitoring information from the OSC signal and sends the information to the SCC board for processing.

Figure 11 Positions of OSC boards in a WDM system

Optical protection boards

Optical protection boards provide 1+1 protection for services using their dual-fed and selective receiving function.

Examples: DCP, OLP, SCS

Different optical protection boards support different types of protection. Figure 12 shows the position of DCP boards in a WDM system when it offers client 1+1 protection.

Figure 12 Position of DCP boards in a WDM system (client 1+1 protection)

Spectrum analyzer boards

Spectrum analyzer boards support centralized monitoring of optical signals without impacting the signal performance.

Figure 13 illustrates the position of spectrum analyzer boards in a WDM system by using the OPM8 board as an example.

Examples: MCA4, MCA8, OPM8 and other boards

Figure 13 Positions of spectrum analyzer boards in a WDM system

Variable Optical Attenuator Board

Electrical variable optical attenuator (EVOA) boards are mainly configured at input ports on optical amplifier (OA) boards, or wavelength-adding and pass-through ports on optical add/drop multiplexer (OADM) boards to adjust optical power.

Examples: VA1, VA4 and other boards

EVOA boards are configured before the input ports of OA boards to adjust the input optical power of OA boards to the OA nominal power or the target power specified in network design. See Figure 14.
Figure 14 EVOA configured at the input port of an OA board
EVOA boards are configured at the wavelength-adding ports and pass-through ports of OADM boards to adjust the optical power of added signals and pass-through signals so that the optical spectrum is flat at an OADM site. SeeFigure 15.
Figure 15 EVOAs configured at the wavelength-adding ports and pass-through ports of an OADM board

Dispersion equalization boards

Dispersion equalization boards compensate for dispersion accumulated during fiber transmission of optical signals and compress the pulses of the propagated optical signals. This enables the propagated optical signals to be restored at the output end.

Examples: DCU, TDC

Table 1 lists the main functions of dispersion equalization boards.

**Table 1** Main functions of dispersion equalization boards
Device Type			Description	Function	Application
Module	DCM	DCM (DCF)	Uses a dispersion compensation fiber (DCF) and provides fixed dispersion.	Provides span-based dispersion compensation, enabling long-haul optical transmission.	Works with optical amplifier boards at the transmit and receive ends of a transmission line. Supports G.652, G.653, and G.655 fiber applications.
Module	DCM	DCM (FBG)	Uses fiber Bragg grating (FBG) and provides fixed compensation.		Works with optical amplifier boards at the transmit and receive ends of a transmission line. Supports G.652 and G.655 fiber applications.
Board	DCU		Uses a DCF and provides fixed dispersion.		Works with optical amplifier boards at the transmit and receive ends of a transmission line. Supports G.652 and G.655 fiber applications.
Board	TDC		Provides tunable dispersion to precisely compensate for dispersion inside a channel.	Precisely compensates for residual dispersion inside an OTU channel that cannot be compensated by DCM modules.	Works with an OTU board at the receive end of a transmission line. The TDC board must precede the OTU board. Applies to scenarios that allow for relatively small dispersion, such as, 40 Gbit/s communication systems.