It is an indisputable fact that ROADM is useless. Before the 5G is about to start, people are advised not to mention or pick up this expensive and useless network weapon.

The Working Principle of ROADM

The working principle of ROADM is shown in the following figure. A, B and C are three station in a WDM system, of which A and C are Optical Terminal Multiplexing (OTM) stations and B is the ROADM station. The service delivered by station A is carried on the wavelengths of λ1 to λ5, where the wavelengths are like the train carriages, and the service is the goods in the carriages. In station B, wavelengths of λ3 and λ5 are downstream, while wavelengths of λ6 and λ9 carry new service upstream, thus realizing directly pass wavelengths (λ1, λ2, λ4), downstream wavelengths (λ3, λ5) and upstream wavelengths (λ6, λ9) at station B. If it is necessary to change the up-down and pass wavelength of B station, it only needs to be configurated by software, and there is no need to make any changes in hardware.

The Working Principle of ROADM

Three Doubts About the Use of ROADM

The principle of ROADM clearly shows that it is only used to flexibly replace wavelengths at a node in the link. Here are three doubts about the use of ROADM.

• Once the wavelength of the system is fixed, the upstream and downstream wavelengths can not be arbitrarily changed to interfere with the business, or take it for granted to turn the west to the east. Because each wavelength in the system plays the same role and function, there is no need to switch the wavelength flexibly.
• Wavelength is not a variable. For business, wavelength is only a physical carrier, and its functions and elements are solidified. Just as stone is stone, and pen is pen. Stones can't be changed into diamonds, and ordinary pens can't be turned into gold pens. For a ROADM network, changing the wavelength is like replacing the same pen in our hands, which is obviously meaningless.
• The use of ROADM in vain increases link loss and cost. The principle and fabrication of ROADM depend on the principle of mechanical optics, and the products are extremely complex and expensive. Although the product itself is a masterpiece, it can not be used wantonly and wasted.

The complex optical structure of ROADM undoubtedly greatly increases the link loss of DWDM system, and is not suitable for mass adoption in high-level networks.

The Advantages of ROADM on the Internet

There are also the following comments about ROADM on the Internet.

Compared with FOADM, ROADM has the following advantages.

• ROADM facilitate the development of new businesses. In the era of mobile communication, new businesses emerge one after another. When large customers need to provide new services at the wavelength level, ROADM only needs to be configured remotely through the network management system.
• ROADM facilitates network planning and reduces operating costs. Low cost can bring more benefits to users, which is also what operators want. ROADM has powerful node reconfiguration capability, which makes the DWDM network reconfigurable easily. Therefore, when network encounters emergencies and needs to be re-planned, ROADM can respond quickly and improve the efficiency of the whole network.
• ROADM is easy to maintain and reduce maintenance cost. Low maintenance cost is always the goal pursued by people. The routine maintenance operations commonly used in ROADM can be carried out remotely through the network management, without sending people to the site to operate, so as to improve work efficiency and reduce maintenance costs.

Why Is ROADM Useless?

The advantages of this assumption are specious. Sometimes we wonder why the industry has such a sophisticated product, but it is flashy. In fact, ROADM is useless.

There are three reasons.
• No matter how many new mobile businesses are emerging, only more wavelengths are needed. All wavelengths specified by ITU are the limits of link configuration. For example, there are 26 letters in English, so no matter how we adjust the order, the 26 letters will never change. For the new services proposed by mobile, what we need to do is to increase wavelengths and equipment, but changing the wavelength can not solve the problem.
• Node reconfiguration seems to give people beautiful technological illusions. But why do we need to reconstruct nodes? If node reconfiguration is switching wavelengths, it seems to be a child's game. Frankly speaking, physical nodes are not Ethernet routing nodes. Physical nodes are based on stability. The reconstruction of network emergencies is also irrelevant to ROADM. What are the sudden incidents encountered by the network? Any network encounter problems must be intervened by human or robot, not by changing a wavelength.
• Can ROADM improve the convenience of maintenance? The answer is no. In fact, ROADM just provides the convenience of maintaining ROADM itself. Because a robust network contains too many things to maintain, regular maintenance is a must. The simpler the network, the less maintenance costs it will be. The maintenance defined by the ROADM network is fundamentally nonexistent.

ROADM is only the spiritual illusion of a generation of technicians. Once deployed, any ROADM network has never been flexibly configured. That means that the industry only adds to the cost and competitiveness of ROADM's deployment without any reason. How puzzling it is!

Conclusion

The optical network is like the earth under our feet and the sky above our heads. The roads on the earth and the routes in the sky must be fixed and precise. Flexible roads and flexible skies do not exist. We can change the means of transportation, but we must not divert the roads and turn the sky upside down at will. Back to the optical network itself, the so-called flexible network should be flexible allocation of bandwidth and flexible configuration of services. But these are independent of wavelength. We need to understand that the nature of any business is independent of wavelength, and wavelength is only related to transmission distance.