With the rapid increase of data traffic by about 40% each year, the dominant 10Gb/s optical networks were soon saturated. 40G was also complemented in existing WDM networks with cost-effective 40G equipment. Yet 40G isn’t enough. Several providers have deployed 100G in long-haul (LH) backbone applications in recent years by using novel fibers and advanced optical components, but overlaying 100G in metro network is still facing many challenges. This post will discuss the requirements for 100G metro network and the challenges faced during this change.
Similar to 10G metro, 100G networks begin with the use of 100G transceivers and dense wavelength division multiplexing (DWDM) multiplexers/de-multiplexers. For some applications, optical amplifiers and dispersion compensation modules are needed.
The metro segment covers a broad range of distances. It can generally be divided to three subcategories: metro access (40 to 100 km), metro core (100 to 500 km) and metro regional (500 to 1000 km). The metro core and the metro regional typically include a large number of reconfigurable-optical-add/drop-multiplexer (ROADM) nodes. The metro access links are generally point-to-point connections.
Although DWDM metro distances are shorter than long-haul links, the transmission requirements for 100G metro are quite challenging with a large number of ROADMs and the fact that the metro fiber is often older and can include many interconnected parts that cause higher loss. In addition, it is likely that 100G metro wavelengths will coexist with existing 10G wavelengths. The coexistence of brownfield and greenfield deployments requires the support of links with and without in-line dispersion compensation. It is essential to use the available fiber bandwidth since installation of new fiber is high cost in a metro environment. Since metro is two or three times larger in size, it is more cost-sensitive and has higher requirements on the space for line-card density than LH networks in achieving the same capacity.
In long-haul networks, coherent transceivers are successfully used. But the size, power consumption and cost of today’s coherent transceivers are not suitable for metro networks where port-density is important. Designing a performance-, size- and cost-optimized single-wavelength coherent 100G metro transceiver is very desirable but quite challenging. To achieve this, C-form factor pluggable (CFP) coherent modules are taking into consideration. CFP coherent modules supporting 10 x 10G and 4 x 25G, and smaller size CFP2 and CFP4 coherent modules supporting 4 x 25G are considered good choices for 100G metro. Another choice is the nonpluggable 4 x 5-inch multisource agreement (MSA) module based on Optical Internetworking Forum (OIF) standards.
Though the 100G metro schemes with coherent modules seem to be clear, there are still questions about pluggable modules. Pluggable slot is generally designed as “universal slot” that could be flexibly used for client- or network-slide optics, but as the client side is moving from CFP to CFP2/CFP4, the ability of such universal slot will be lost unless the coherent modules keep pace.
As mentioned before, unlike LH links, metro consists of a lot of ROADMs. To achieve 100G performance, the metro needs to handle the increased loss created by growing number of ROADMs. Also it has to deal with the higher loss in old fiber to ensure desired transmission quality.
Also there are many challenges in satisfying requirements for low power consumption, high port density, low latency, and standardized data-rate and modulation formats for 100G metro network.
There is still a long way to go for the implementation of cost-effective and high-performance 100G metro network. However, the challenges in network and optical areas will finally turn to reasons for the achievements in metro network development. The cost will be driven down and the applications of 100G metro will be prevalent. FS.COM provides major brands compatible QSFP28, CFP and CFP2 modules and generic CFP4 modules for your upgrading to 100G infrastructures. If you are in need of other fiber optic modules, you can also visit our web site for more information.
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