Shulou(Shulou.com)11/24 Report--

With our mobile phones and computers every day, we can browse Weibo, watch videos and chat on Wechat fluently. These simple daily activities need to be supported by a large-capacity transportation system. Otherwise, Weibo, video, Wechat information can not be accurately delivered to your mobile phone or computer screen. One of the technologies that have to be mentioned in this large-capacity transportation system is WDM / OTN.

WDM (Wavelength Division Multiplexing, WDM) is a technology that uses different optical waves to carry different services and transmits multiple services in the same optical fiber at the same time. OTN (Optical Transport Network, Optical Transport Network) can be understood as the optimized upgrade version of WDM. Let's talk about these two technologies.

1. What is WDM? If the optical fiber is compared to a highway, and the light wave used for transmission business in the WDM system is compared to a truck, Weibo, video, Wechat and other different transmission services are equivalent to packages to be transported, which are placed directly on different trucks. If these trucks want to enter the optical fiber transmission regardless of the lane, then the rush in will cause chaos and disorder in the traffic flow of the whole highway and affect the transmission efficiency. With WDM, different transmission services can be transmitted on the same optical fiber at the same time, which is equivalent to dividing lanes for different vehicles on the highway, allowing different vehicles to run in different lanes at the same time, and improving the transmission efficiency.

At the same time, to ensure smooth traffic, we need to distinguish between lanes and let different vehicles go their own way. Similar to the road traffic division of large lanes and small lanes, the lane division in WDM system is divided into two types: CWDM (Coarse Wavelength Division Multiplexing, sparse wavelength division multiplexing) and DWDM (Dense Wavelength Division Multiplexing, dense wavelength division multiplexing). The lane spacing of the former is larger, generally 20 nm, while the latter is smaller, generally less than 0.8 nm.

2. What does the WDM system consist of? As long as the lane is divided, can WDM allow different services to be transmitted on the same optical fiber at the same time? It's not that simple. Let's take a look at how WDM does it.

In technical terms, WDM systems are generally composed of OTU (Optical Transponder Unit, optical forwarding unit), combinator / splitter unit, monitoring channel and optical amplifier unit.

So, how do the various parts of WDM work together to complete business transmission? Let's take a look at the transmission process of business in WDM.

In order to transmit the service in WDM, it is necessary to send the service to the proprietary vehicle of WDM (that is, OTU unit) and convert these service signals into standard wavelength optical signals recognized by WDM.

The standard wave light signal vehicle carrying the service is driven to the checkpoint (that is, the combined wave unit), and is arranged to enter different lanes through the checkpoint, and one vehicle is driving on the highway at the same time.

The driving condition of the vehicle needs to be supervised by the patrol car, that is, the monitoring channel to ensure that the service transmission is normal.

If the transportation distance is long, it is also necessary to let the vehicle drive into the unified gas station, that is, through the optical amplification unit, the business signal is regenerated and amplified to ensure that there is no damage to the long-distance transportation of the business.

When the service is transported to the terminal, the vehicle comes out from the inspection station (that is, the wave division unit) and diverts to the corresponding receiving customer terminal exit, and the service is unloaded from the vehicle, that is, it is converted into the customer service signal (that is, the service signal without wavelength information) through the OTU unit, and sent to the customer.

3. What is OTN? From the brief introduction above, it is not difficult to conclude that the greatest advantage of WDM technology is that it makes good use of optical fiber resources and can provide large-capacity data transmission capacity. But WDM has the following obvious disadvantages:

If the business "package" on the WDM vehicle goes wrong during transportation, there is no way to identify it. That is, the ability of WDM system to monitor, manage, operate and maintain the business is weak.

If a service specifies the channel transmission in the WDM system, the channel can no longer be used by other services, which will result in a waste of resources. For example, on the highway, each type of vehicle takes a fixed lane, and if the lane is free, other types of vehicles are not allowed to take this lane.

With the development of the communication network, the amount of data on the data network increases rapidly, experts have to continue to develop the potential of WDM and improve the ability of WDM, so a new technology is born-OTN.

It is said that the WDM system is similar to the highway traffic system, while OTN is an upgraded version of the highway traffic system, and its upgrade function is mainly shown in the following two aspects:

To increase the operation and maintenance rules, the specific measure is to increase the frame structure to improve the monitoring, management, operation and maintenance capabilities of the business.

From the comparison of the simplified WDM and OTN systems above, you can see:

In the WDM system, only the non-wavelength information service entering the WDM system is converted into a wavelength information service, which is transmitted to the WDM system. In other words, the WDM system has no supervision mechanism for the transmitted service, and only ensures that the service can be transmitted to the receiver.

In the OTN system, it provides a set of rules for putting services into the OTN system, that is, the so-called frame structure requirements. Services entering the OTN system will first be packaged according to the requirements of the OTN frame structure, that is, the information of monitoring and management operation and maintenance will be added, and then converted into services with wavelength information to be transmitted to the OTN system.

The function of electrical crossover is added so that the OTN system can deal with customer service signal and wavelength division signal respectively.

"what does the WDM system consist of?" When it is mentioned that the WDM system can transmit customer services, first of all, it is necessary to convert the customer service signals into wavelength division signals. When dealing with this function, the traditional WDM system is directly realized through the same single board, corresponding to each customer service needs to occupy a light wave carrier. When there are more and more types of customer services in the network, in order for these services to be transmitted in the WDM system, on the one hand, we need to develop a new veneer that carries these services, which will increase the cost of network construction; on the other hand, these services will also occupy more light waves, resulting in a shortage of resources. Therefore, the OTN system introduces the electric crossover function, which is like adding a cargo dispatching center in the traditional WDM transportation system. The cargo dispatching center will pack and dispatch different goods (that is, different services) that enter the OTN transportation system and put them into different vehicles (that is, they are carried by different light waves).

The advantage of the cargo dispatching center is that if the network adds new customer services, it only needs to increase the customer-side veneer connected to the new service, and borrows the existing veneer transport service on the line side to save the cost of network construction. At the same time, when the truck in a certain lane is free, it can load the customer service to the truck at any time through the cargo dispatching center, so as to avoid the truck running over the lane and wasting resources.

To sum up, OTN is actually an optimization of WDM, further improving the operation and maintenance capability and flexible resource scheduling capability of the WDM system.

In a word, with the rapid expansion of information data, WDM / OTN technology acts as a large-capacity transportation system of data network, constantly transmitting these information and data "goods" with higher reliability, higher flexible scheduling capacity and higher resource utilization.

This article comes from the official account of Wechat: ZTE document (ID:ztedoc), author: ZTE document

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