On account that DWDM (Dense Wavelength Division Multiplexing) technology can make full use of the huge bandwidth resources of the optical fiber, greatly increasing the transmission capacity of the system and reducing the transmission cost, the technology has been widely used in the large-capacity transmission of long distance network and backbone network.
If DWDM technology is introduced into the metropolitan area network and access network, the whole network will become a whole of seamless connection, providing support and connection for all different services. Therefore, the DWDM system in the metropolitan area network has great superiority and development potential, which will become the inevitable evolution of the whole communication network to the all-optical network.
Why Use DWDM System in the Metropolitan Area Network(MAN)?
In the past, the SDH (Synchronous Digital Hierarchy)/SONET(Synchronous Optical Network) is the core component of the metropolitan area network. However, this technology is with limitations. For example, it is highly structured, simplex in the interface and limited on bandwidth; simultaneously, it also can not meet the diverse needs of enterprises; in addition, its cost is relatively high in the installation and operation of Ethernet by SDH/SONET technology.
DWDM technology is an alternative solution for SDH/SONET technology. It is with flexibility and wide application. The DWDM system can carry SDH, PDH, and other unrestricted digital signals or analog signals. Therefore, vendors and enterprises can use DWDM technology to provide a variety of services. The metropolitan area network based on DWDM technology can make full use of the huge bandwidth resources of the optical fiber, greatly improving the transmission capacity of the system and reducing the transmission cost.
Factors to be considered for the Application of DWDM in the MAN
The application of DWDM technology in metropolitan area network is mainly determined by 3 factors: market demand, technology development and operation cost. Market demand is the fundamental reason for the entry of DWDM technology into the metropolitan area network; the tech factor is the effective guarantee for DWDM technology to enter the metropolitan area network.
The cost of DWDM is also an important consideration factor for operators to adopt DWDM. Analyzing the particularity of the metropolitan area network and improving the DWDM system to reduce the price, it is the key of the DWDM technology to gradually penetrate into the metropolitan area network&access network from the backbone network, and finally to realize the all-optical-network.
Networking Scheme of DWDM in the MAN
MAN is generally divided into metropolitan core network and metropolitan access network. Metropolitan core network mainly takes 2.5Gb/s SDH as the integrated transmission platform, which will be gradually evolved in the DWDM integrated transmission platform.
According to different developmental stages and different application fields, DWDM mainly has three application solutions. The three basic solutions match with different superstructure schemes, which can constitute various metropolitan core schemes to adapt to application conditions and development requirements of different operators.
1. DWDM Optical Multiplexing Scheme
DWDM as the multiplexing tech is introduced into the metropolitan core network, only taking optical wavelength as the virtual optic fiber to solve the tense situation of the optic fiber. Currently, DWDM MAN device enters into the market basically in this method. Because of the lack of path selection, monitoring and survivability processing in the WDM optical layer, the scheme still takes SDH as the integrated transmission network platform.
2. DWDM Configurable Halo Scheme
With the continuous introduction of the DWDM optical multiplexing system in the metropolitan core network and the practicability of the configurable OADM, DWDM configurable halo scheme of the metropolitan core network can be formed by combining configurable OADM system with DWDM system. This scheme greatly enhances the function of the WDM optical layer. OADM can be configured selectively up/down/direct connection with the optical wavelength so as to achieve fast protection switching and configuration.
The DWDM configurable halo scheme enables DWDM to replace SDH as a multi-services platform. It also supports various protocols and services through a single and public metropolitan core integrated transmission platform based on DWDM, and it is with these advantages such as forward compatibility (such as SDH over WDM), reducing costs (by simplifying the network hierarchy structure, reducing equipment and improving transmission efficiency), simplifying network management and improving the flexibility of network configuration.
3.DWDM Mesh Network Scheme
After the OXC with wavelength switching/routing function is put into practical application, OXC can be introduced to constitute a more complex mesh network structure on the basis of DWDM configurable halo. OXC or wavelength router is very flexible. Common OXC nodes can contain the up/down optical paths and protection function of OADM in the chain/ring structures and can reconfigure OXC to gradually develop toward multi-rings or pure mesh network structure without interrupting the services.
DWDM has been widely applied in the long-haul trunk line. In MAN, due to the high cost of devices, immature tech, poor compatibility of devices, etc, DWDM is still hard to be widely applied in the MAN. But with the further development of the market and the advancement of tech, new MAN devices with low cost will be developed for application on account that DWDM tech is with economic efficiency in capacity expansion, good extensibility, transparency in bit rate and protocol, and also is able to provide improved service quality. Therefore, DWDM tech is with a bright prospect in the MAN.
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