Current situation, existing problems and developme

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The current situation, existing problems and development trend of CWDM products

due to the rapid development of data services, the speed of network integration is accelerating, and metro is becoming the hot spot of current network construction, and the pressure of market competition makes telecom operators more sensitive to network costs (including construction costs and operation and maintenance costs). In response to this market demand, low-cost Metro CWDM products came into being

with the strong promotion of CWDM Technology by all optical spectrum CWDM Alliance (FCA) and the standardization of CWDM by ITU-T, CWDM Technology has become the focus of equipment manufacturers and operators. In May, 2002, ITU-T Research Group 15 passed the standard g.694.2 of CWDM wavelength grid, which became a milestone in the development history of CWDM Technology. The 15th research group also proposed the PP standard draft to define the CWDM system interface. Chinese enterprises such as Shanghai Bell have also made some contributions to the standardization of CWDM Technology, and relevant domestic standards are also under discussion

with the growth of market demand and the rapid standardization of CWDM Technology, many domestic and foreign communication equipment manufacturers, such as Nortel, ciena, Huawei, Alcatel Shanghai Bell, Fiberhome, etc., have developed related products and have been widely used in the market

this paper briefly introduces the principle and advantages of CWDM, and analyzes the current situation, existing problems and development trend of CWDM Technology Combined with the test results of several CWDM products

cwdm system principle

cwdm (coarsewaverengthdivisionmultiplexing) system, namely sparse wavelength division multiplexing system, is a low-cost WDM transmission technology for metropolitan access layer. In principle, CWDM uses optical multiplexers to multiplex optical signals of different wavelengths to a single optical fiber for transmission. At the receiving end of the link, with the help of optical demultiplexers, the mixed signals in the optical fiber are decomposed into signals of different wavelengths and connected to the corresponding receiving equipment. Its principle is shown in Figure 1. The main difference between CWDM and DWDM is that compared with the wavelength interval of 0.2nm to 1.2nm in DWDM system, CWDM has a wider wavelength interval, and the standard wavelength interval commonly used in the industry is 20nm. The wavelengths specified in ITU-T g.694.2 are shown in Table 1. The bands of each wavelength are shown in Figure 2, covering the five bands of O, e, s, C, l of the single-mode optical fiber system

due to the wide wavelength spacing of the CWDM system, the requirements for the technical indicators of the laser are low. As the wavelength interval reaches 20nm, the maximum wavelength offset of the system can reach -6.5 ℃ ~ + 6.5 ℃, and the accuracy of the emission wavelength of the laser can be relaxed to ± 3nm. Moreover, within the working temperature range (- 5 ℃ ~ 70 ℃), the wavelength drift caused by temperature change is still within the allowable range. The laser does not need a temperature control mechanism, so the structure of the laser is greatly simplified and the yield is improved

in addition, the larger wavelength interval means that the structure of optical multiplexer/demultiplexer is greatly simplified. For example, the number of coating layers of filter in CWDM system can be reduced to about 50, while the number of coating layers of 100GHz filter in DWDM system is about 150, which leads to improved yield and reduced cost, and the supplier of filter is greatly increased, which is conducive to competition. The cost of CWDM filter is more than 50% less than that of DWDM filter, and will be further reduced with the increase of automatic production technology and batch

in addition, CWDM is positioned for short-distance transmission (within 80 kilometers) in the metropolitan area network, and the channel rate generally does not exceed 2.5Gbps, so there is no need to consider optical amplification, dispersion, nonlinearity and other aspects in the transmission line, so the system can be simplified

through the above means, through the expansion of wavelength spacing and the simplification of equipment, the cost of unit optical channel of CWDM system can be reduced to 1/2 or even 1/5 of DWDM system, which has strong advantages in the metropolitan access layer

advantages of CWDM products

the most important advantage of CWDM is the low cost of equipment. The details have been introduced earlier. In addition, another advantage of CWDM is that it can reduce the operation cost of the network. Due to the small size, low power consumption, simple maintenance and convenient power supply of CWDM equipment, 220V AC power supply can be used. Due to the small number of wavelengths, the amount of board backup is small. Using 8-wave CWDM equipment has no special requirements for optical fibers. G.652, G.653 and G.655 optical fibers can be used, and existing optical cables can be used

cwdm system can significantly improve the transmission capacity of optical fiber and improve the utilization of optical fiber resources. The construction of metropolitan areas is facing a certain degree of tension in optical fiber resources or the high price of renting optical fibers. At present, the typical coarse wavelength division multiplexing system can provide 8 optical channels, and is committed to creating a more transparent and environmentally friendly package. According to ITU-T g.694.2 specification, it can reach 18 optical channels at most

another advantage of CWDM is its small size and low power consumption. The laser of CWDM system does not need semiconductor cooler and temperature control function, so it can significantly reduce power consumption. For example, each laser of DWDM system consumes about 4W power, while the CWDM laser without cooler consumes only 0.5W power. CWDM soybean oil and soybean filler are expected to replace automotive rubber when used together. Using the simplified laser module in the system with China's petroleum base content of up to 26%, the volume of its optical transceiver integration module is reduced, and the simplification of equipment structure also reduces the volume of equipment and saves room space

compared with the traditional TDM mode, CWDM has speed and protocol transparency, which makes it more suitable for the development of metropolitan high-speed data services. There are many services with different protocols and different rates in the metropolitan area. CWDM provides transmission channels that provide different rates on one optical fiber and are transparent to the protocol, such as Ethernet, ATM, POS, SDH, etc. Moreover, the transparency and add drop multiplexing function of CWDM can allow users to directly go up and down a certain wavelength without converting the format of the original signal. That is, the optical layer provides a transmission structure independent of the service layer

cwdm has good flexibility and scalability. For Metro business, the flexibility of business provision, especially the speed of business provision and the ability to expand with business development, is very important. CWDM Technology can be used to open services for users in one day or several hours, and with the increase of business volume, the capacity can be expanded by inserting a new OTU board

improve business quality. The application of CWDM system in metropolitan area can make the optical layer recovery possible. Light layer recovery is much more economical than electric layer recovery. Considering that the optical layer recovery is independent of service and rate, some systems without protection function (such as Gigabit Ethernet) can be protected by CWDM

due to the above advantages of CWDM Technology, CWDM has been more and more applied in telecommunications, radio and television, enterprises, campuses and other fields

cwdm product status

in order to study the status and existing problems of CWDM Technology, we invited Huawei, Alcatel Shanghai Bell, ciena, optical bridge, Shanghai all optical network, Fiberhome network and other manufacturers to conduct CWDM equipment testing. The main testing contents include: main optical channel MPI interface testing, OTU testing, service interface testing (including SDH, Ethernet, transparent rate channel interface, ESCON, etc.); Group capability test (including OADM ring, point-to-point, chain shape, single fiber bidirectional, etc.), optical layer protection function test, tube function test, reliability (high and low temperature, humidity, vibration, etc.) and equipment safety test. Through this test, we can see that the current CWDM Technology has the following main characteristics:

1. Because the current E-band optical transceiver module technology is not mature, the vast majority of products are 8-wave (1470nm~1610nm). Because CWDM Technology is positioned at the edge layer of the metropolitan area, relevant products are designed as box products, and can be easily expanded through cascading

2.cwdm supports point-to-point, chain, ring, band chain, single fiber bidirectional and other groups, which can be used flexibly according to needs

3. generally, it supports 1 + 1 optical line protection of MUX line side dual transmitter and receiver, and also 1 + 1 optical channel protection of OTU layer through special protection board

4. Because there are many kinds of Metro services, such as GE, SDH, Fe, ESCON, FICON, FC, etc., and the rate may be 100mbit/s ~ 2.5gbit/s, CWDM has the protocol transparency and rate transparency, so it can well provide the transmission function of multi services in the metro

5. Many manufacturers begin to support the service multiplexing function of the electric layer. For example, Shanghai Bell can multiplex signals with a rate of less than 622m in different formats into 4% of STM-16 signals × Any board, Huawei's gemux board, can multiplex two Ge or FC into STM-16

6. CWDM network management system has weak ability in performance management, fault management and configuration management, which needs to be further improved

7. There are still some deficiencies in the reliability and safety of some CWDM equipment, such as the lack of ALS or APR function, and the reliability of optical transceiver module needs to be improved. These problems are the result of emphasizing cost reduction

make it occupy the right position

problems of CWDM products

the biggest problem of CWDM Technology is that its cost advantage over DWDM equipment is still not obvious. Optical transceiver modules and optical devices are the key to reduce costs. However, due to the small size of the market and the small shipment volume of suppliers, the cost advantage of devices is not obvious

another way to reduce costs is to simplify equipment functions, which leads to the reduction of system reliability and manageability

DWDM products with decreasing prices also put great pressure on CWDM Technology, and DWDM technology can form a complete metropolitan DWDM, so it has good scalability and great pressure on CWDM

at present, the number of optical channels (wavelengths) supported by CWDM equipment is no more than 8, mainly because the manufacturing process of E-band optical transceiver module is not mature. In addition, g.652c optical cable, which eliminates the water absorption peak, is rarely used in today's applications, so the market demand for E-band optical transceiver module is not large

CWDM system with higher rate and longer transmission distance still has many technical problems. Such as the dispersion problem of 10G system, ultra wideband optical amplification technology, etc

in addition, the standardization process needs to be accelerated, especially the guidance of operators in terms of business interface functions

development direction of CWDM products

at present, one of the key factors restricting the development of CWDM products is the price of optical transceiver modules and multiplexing and demultiplexing devices. With the development of the market and the progress of manufacturing technology, further reducing the cost of equipment is an important development direction

develop E-band optical device technology to make it mature as soon as possible. Develop 10g rate optical channel technology to improve the capacity and scalability of CWDM system

supporting various business interfaces is the development direction of CWDM. The demand of metropolitan access layer for multi service interfaces is the driving force for manufacturers to further develop multi service interfaces. CWDM equipment will provide Fe, Ge, SDH, ESCON, FC and other business interfaces. Another development direction is that it can be combined with MSTP or high-performance routing switching equipment as a means for MSTP equipment or high-speed router to expand line side capacity

providing multi-level optical layer and business layer protection functions is also a development direction to meet the needs of different customers

network management technology and equipment safety, reliability and other aspects are further improved to improve competitiveness in the market

for the newly launched g.652c optical fiber, the price of g.652c optical fiber is twice that of g.652b, and the E-band

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