Metropolitan area network (MAN) refers to the network that covers the city and its suburbs, providing integrated transmission platform for metropolitan areas. MAN has gained widespread acceptance and is extensively applied in both large and medium-sized cities, for the purpose of realizing voice, data, images, multimedia and IP access. Recently, CWDM technology has emerged as a widely accepted solution for long-haul metro networks, by taking the advantage of reduced system cost, sound performance and easy maintenance. As well as making economic and practical sense.
CWDM (Coarse Wavelength Division Multiplexing) technology appears to be an ideal solution to help carriers maximize their network capacity in the access, metro and regional network segments. It supports fewer wavelengths than DWDM, but is available at a fraction of the cost of DWDM, making it attractive for areas with moderate traffic growth projections. CWDM presents a cost-effective alternative to DWDM in many metro and regional networks, while providing a capacity boost in the access networks. Additionally, CWDM is simpler and easier to implement when compared with DWDM, and it generally meets the bandwidth growth demands without overbuilding the infrastructure. Let’s just take a typical 8-channel CWDM system for instance. While inexpensive to deploy, offers 8 times the amount of bandwidth that can be achieved using a SONET/SDH system, for a given transmission line speed and using the same optical fibers.
Features and advantages that CWDM system generally processes make it shine out for deploying in metro networks. Which includes the following factors.
Firstly, ITU-T G.694.2 defines 18 wavelength for CWDM transport ranging from 1271 to 1611 nm, spaced at 20 nm apart. 20 nm wavelength interval was chosen to allow the effective use of low-cost, uncooled lasers and wideband filters in CWDM systems. Which eliminates the need for large, power-consuming thermo-electric cooling circuitry in CWDM systems. And the uncooled laser design also largely accounts for the small size, low cost and low power consumption of CWDM systems.
Additionally, CWDM systems simplify network design by removing the need for optical amplifiers, instead, they utilize optical signal regeneration at every node. We know that for a high capacity DWDM system, attempting full regeneration of all wavelength at each node is rather expensive and complex. CWDM is nothing like DWDM in this case. Due to the small number of wavelength, inexpensive optics and compact size, the total cost of regenerative CWDM systems can be kept low. And with flexible add-drop capability and network design simplicity, CWDM systems are gaining in increasing popularity in metro networks.
Thirdly, the distance between two CWDM termination points can span up to 100 km, depending on the interface speed and the quality of optical fibers. Which makes regenerative CWDM systems suited for applications in the metro-regional space.
Metro CWDM networks fill in the gap between the high capacity, regional and long haul DWDM networks and the emerging NG-SONET networks. In particular, regenerative CWDM networks and NG-SONET networks fulfill complementary needs in the metro space.
Regenerative CWDM networks enable wavelength services to be provisioned over a large metro area, with the functional and economic benefits of full logical mesh connectivity, wavelength re-use and low end-end latency. These features are applicable to the Inter-Office (CO-CO) and Fiber to the Building (FTTB) segments of the metro network. The low latency benefits of CWDM are especially attractive in ESCON and FICON / Fibre Channel based SAN applications.
The low space, power and cost benefits of CWDM also enable its deployment in the Outside Plant (OSP) or Remote Terminal (RT) segments of the metro market. This is the final bottleneck in the bandwidth chain from the service provider to the end-customer. CWDM pair-gain technology enables new broadband services to be deployed from remote OSP cabinets without forklift upgrades to the existing equipment that provides the basic (POTS) services.
CWDM technology is considered to be an attractive solution for carriers who need to upgrade their networks to accommodate current or future traffic needs while minimizing the use of valuable fiber stands. From discussed above, it is clear that CWDM has more merits than DWDM in the metropolitan area networks, while possesses superior economic advantages as well. Given the low cost, simplicity, scalability and management features of CWDM systems, with the ever-lasting traffic demands, the application of CWDM in the access and metro networks will continue to rise.
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