Tag Archives: optical transport network

DWDM Network over Long Distance Transmission

With the ever-increasing need for higher bandwidth, DWDM technology has been one of the most favorable optical transport network (OTN) applications. In this post, we will reveal FS.COM DWDM-based network solutions over various transmitting distances as well as some suggestions for the DWDM networks deployment.

DWDM Networks Basics

As usual, let’s review some basics of DWDM networks. In this part, we will figure out two questions: What is DWDM? What are the components of DWDM networks?

DWDM Technology
DWDM Networks

Figure 1: DWDM Networks

DWDM (Dense Wavelength Division Multiplexing) is an associate extension of optical networking. It can put data signals from different sources together on a single optical fiber pair, with each signal simultaneously carried on its own separate light wavelength. With DWDM, up to 160 wavelengths with a spacing of 0.8/0.4 nm (100 GHz/50 GHz grid) separate wavelengths or channels of data can be transmitted over a single optical fiber.

DWDM Networks Components

Conventionally, for DWDM networks, there are four devices showed as below that are commonly used by IT workers:

  • Optical transmitters/receivers
  • DWDM mux/demux filters
  • Optical add/drop multiplexers (OADMs)
  • Optical amplifiers transponders (wavelength converters)

DWDM Networks Over Long Distance Transmission Solutions

Scenario 1: 40 km Transmission
40km DWDM Network

Figure 2: 40km DWDM Network

For this case, the 80km DWDM SFP+ modules and 40ch DWDM Mux/Demuxs are recommended to use. Since the 80km DWDM SFP+ modules are able to support 10G transmission over 40 km, no additional device is needed under this scenario.

Scenario 2: 80 km Transmission
80km DWDM Network

Figure 3: 80km DWDM Network

Deploying this 80 km DWDM network, we will still use 80km DWDM SFP+ modules and 40ch DWDM Mux/Demuxs. The light source of 80km DWDM SFP+ modules might not be able to support such long transmission distance, as there might be a light loss during transmission. In this case, pre-amplifier (PA) is usually deployed before the location A and location B to improve the receiver sensitivity and extend signal transmission DWDM distance. Meanwhile, the dispersion compensation module (DCM) can be added to this link to handle the accumulated chromatic dispersion without dropping and regenerating the wavelengths on the link. The above diagram shows the deploying method of this 80km DWDM network.

Scenario 3: 100 km Transmission
100km DWDM Network

Figure 4: 100km DWDM Network

Under this scenario, the devices used in scenario 2 still need to remain. Since the transmission distance has been increased, the light power will be decreased accordingly. Besides that, you will also need to use booster EDFA (BA) to amplify the optical signal transmission of the 80km DWDM SFP+ modules.

By the way, if you want to extend DWDM transmission distance, you can read this post for solutions: Extend DWDM Network Transmission Distance With Multi-Service Transport Platform.

Factors to Consider in Deploying DWDM Networks

1. Being compatible with existing fiber plant. Some types of older fiber are not suitable for DWDM use. Currently, standard singlemode fiber (G. 652) accounts for the majority of installed fiber, supporting DWDM in the metropolitan area.

2. Having an overall migration and provisioning strategy. Because DWDM is capable of supporting massive growth in bandwidth demands over time without forklift upgrades, it represents a long-term investment. Your deployment should allow for flexible additions of nodes, such as OADMs, to meet the changing demands of customers and usages.

3. Network management tools. A comprehensive network management tool will be needed for provisioning, performance, monitoring, fault identification and isolation, and remedial action. Such a tool should be standards-based (SNMP, for example) and be able to interoperate with the existing operating system. For example, the FMT DWDM solutions from FS.COM are able to support kinds of network management, including NMU line-card, monitor online, simple management tool, and SNMP.

4. Interoperability issues. Because DWDM uses specific wavelengths for transmission, the DWDM wavelengths used must be the same on either end of any given connection. Moreover, other interoperability issues also need to be considered, including power levels, inter- and intra-channel isolation, PMD (polarization mode dispersion) tolerances, and fiber types. All these contribute to the challenges of transmission between different systems at Layer 1.

5. Strategy for protection and restoration. There might have hard failures (equipment failures, such as laser or photodetector, and fiber breaks) and soft failures such as signal degradation (for example, unacceptable BER). Therefore, you need to have a protection strategy while deploying a DWDM network.

6. Optical power budget or link loss budget. Since there might be an optical signal loss over the long distance transmission, it’s critical to have a link loss budget in advance.


Bringing great scalability and flexibility to fiber networks, the DWDM networks solutions obviously enjoys plenty of strengths, which is also proved to be future-proof. In this post, we make a revelation of the DWDM-based network over long distance transmission. Also, some tips for deploying a DWDM network has also been shared for your reference.

FMT 4000E for DWDM Network Solution

In the network era, the demand for greater traffic capacity, higher bandwidth, and better performance over longer transmission distance have never stopped. Under such a context, the optic transport network (OTN) has undergone great changes to survive. At the moment, FS provides their all-in-one dense wavelength division multiplexing (DWDM) OTN solutions. In this post, we will share one of the most popular DWDM solutions: FMT 4000E.

DWDM Network Basics


Dense wavelength division multiplexing is a technology based on wavelength-division multiplexing (WDM). It combines or multiplexes data signals from different sources for transmissions over a single fiber optic cable. At the same time, data streams are completely separated. Each signal is carried on a separate light wavelength. In most cases, the dense wavelength division multiplexing technology is applied in metropolitan network.

Optical Transport Network

Defined by the ITU Telecommunication Standardization Sector (ITU-T), OTN is a set of optical network elements (ONE) that are connected by optical fiber links. Sometimes, it’s also called the digital wrapper technology which provides an efficient and globally accepted way to multiplex different services onto optical light paths. This technology provides support for optical networking by using WDM unlike its predecessor SONET/SDH. It’s able to create a transparent, hierarchical network designed for use on both WDM and time division multiplexing (TDM) devices. The OTN is able to support functions, like transport, multiplexing, switching, management, supervision, and builds OTN client (e.g. SONET/SDH, IP, ATM) connections in the Metro and Core networks.

Optical Transport Network

Figure 1: Optical Transport Network

DWDM Network

The DWDM based network refers to a kind of dense wavelength division multiplexing technology based OTN solution. Compared with CWDM, the DWDM uses more sophisticated electronics and photonics, which makes its transmitting channel are narrower than CWDM channels. Therefore, for a DWDM network, it can support more channels and separate wavelengths (up to 80 wavelengths). It can transmit data in IP, ATM, SONET, SDH, and Ethernet. For it’s protocol and bitrate independent, the DWDM-based OTN networks can carry different types of traffic at different speeds over an optical channel.

DWDM vs CWDM Wavelength

Figure 2: DWDM vs CWDM Wavelength

FMT 4000E for DWDM Solution

In order to make the DWDM OTN deployment easier, FS has launched the high integration FMTWDM transport networks, such as FMT 1800 and FMT 9600E. In this post, we will mainly introduce the most popular solution: FMT 4000E.

What Is FMT 4000E

The FMT 4000E is a device that combines the OTN switching and dense wavelength division multiplexing features and provides unified transmission of all services. It integrates DWDM equipment with OTN function cards (EDFA, DCM, OEO) in a 4U form factor. With FMT 4000E, you can extend the optical link power budget for building long-distance dense wavelength division multiplexing solutions.

FMS 4000E

Figure 3: FMT 4000E

Strengths of FMT 4000E
  • Supports up to 40 wavelengths via the dual fiber bi-directional transmission mode.
  • Transmits up to 100 km with DWDM SFP+ 80km at the rate of 10Gbps.
  • Optional function cards to meet various needs (WDM Mux/Demux, EDFA, DCM, OEO).
  • Dual AC or DC pluggable power supply and fan unit.
  • Supports SDH/SONET, PDH, Ethernet, SAN, LAN, video service transport.
  • Scales easily for the ring, end to end and mesh networks.
  • Suitable for the enterprise, medical, Storage Area Networks (SANs), data centers, campus optical network and video surveillance.
  • Scalable solution for customers to expand capacity as needed. And operating costs and vital resources are greatly saved.
  • Ensure the maximum bandwidth for the required capacity and transmission distances.
  • Fully managed, configured and monitored remotely via FS.COM intelligent network management unit.
  • Simple installation, operation, and maintenance.
  • Standards-based and can integrate with third-party solutions.
  • The solution can be customized to suit specified customer application requirements.
Solution Topology
FMS 4000E Solution Topology

Figure 4: FMT 4000E Solution Topology

Note: This solution does not come with OPM, OPD, OLP, OSW card.

Matching Products
  • 40CH C21-C60 DWDM Mux Card ( 2pcs)
  • 40CH C21-C60 DWDM Demux Card ( 2pcs)
  • 20dB Gain Pre-Amplifier DWDM EDFA Card (2pcs)
  • 17dB Output Booster EDFA Card (2pcs)
  • 40km Passive Dispersion Compensation Card (4pcs)
  • FMT 4U Managed Chassis (2pcs)
  • LC/UPC Single Mode Fixed Fiber Optic Attenuator, 3dB (1pc)


Obsessed with higher bandwidth applications and the simplest operation, the OTN has broken through its traditional operation and make inroads into the highly integrated OTN. Undoubtedly, the DWDM solution will be the one having the last laugh after networking ups and downs. To share that last laugh, FS provides its DWDM solutions for multi-service optical transport over ultra-long distance: FS WDM Multi-service Transport (FMT) series. They help our customers to build an access transport network with more flexible service access, easier operation, and lower OPEX.