As we know, nearly all metro networks are based on the WDM architecture. However, WDM systems operating at 10Gbps and 40Gbps per fiber are becoming saturated since data traffic volume increases quickly. To solve this, the WDM system with 100Gbps per fiber is introduced as a cost-effective way to expand capacity for metro optical transport networks. Therefore the 100G metro network is booming now.
In traditional 10G and 40G metro networks, operators choose either passive and fixed-filter technology or ROADM technology to deploy the optical network. The fixed-filter metro network delivers low-cost, simple point-to-point connectivity but lack of flexibility and scalability, while a ROADM-based metro network provides easy-to-operate and flexible any-to-any connectivity at a high initial installation cost.
Unlike 10G and 40G metro networks, the 100G metro network mainly uses the newly-developed coherent packet-optical technology which provides flexibility and scalability as much as the ROADM-based network but without its costly wavelength selective switches (WSS) and optical filters. With the coherent technology, wavelengths in the 100G metro network can go from any site to any site, with any spectral width and centered on any frequency, making the network both flexible and future-proof. In addition, the direct detect technology is also emerged as another solution for metro access Data Center Interconnectivity (DCI), particularly in DCI connections with spans less than 80km. For more details on coherent and direct detect technologies, please visit 100G Metro Data Center Interconnectivity (DCI): Coherent vs. Direct Detection
Here are the main benefits of the 100G metro network with coherent packet-optical technology:
Higher capacity: the 100G metro network provides 100Gbps per fiber, allowing network operators to meet customers’ need for more bandwidth;
Cost-efficiency: coherent technology in 100G metro network can help to continually reduce cost per bit via advanced technology innovations;
High competitiveness: the 100G metro network helps to increase the network provider’s competitiveness by doing more with less and the ability to turn up services faster.
A metro transport network can typically be divided into three sublayers: national or core layer, regional layer and aggregation layer. And the last two layers provide transport function within different technologies – IP RAN and PTN for mobile networks, and IP packet routing/switching for fixed broadband access.
Figure 1: 100G Metro Transport Network Sublayers
Similar to the 10G and 40G metro networks, the 100G metro network begins with the use of 100G DWDM transceivers and dense wavelength division multiplexing (DWDM) Mux Demux in the above-mentioned core and regional layers. In addition, optical amplifiers and dispersion compensation modules are also needed in some application scenarios. The following picture illustrates the basics of one node in the 100G metro network core and regional layers:
Figure 2: Basics of One Node in100G Metro Network Core and Regional Layers
The 100G DWDM CFP coherent transceiver is now the major transceiver used in 100G metro networks. It uses four lasers, each tunable over the DWDM grid, such that the resulting link realizes 4 x 25 Gb/s with each 25 Gb/s traveling in a separate single-mode duplex fiber.
The DWDM Mux Demux is the core technology providing a platform for adding essentially unlimited co-propagating channels to existing 10G and 40G channels with the 100G upgrades and eventually making it possible to upgrade all channels to 100G.
An optical amplifier is used to overcome the additional loss encountered from the fiber attenuation, optical power splitting, and other factors. And the dispersion compensation module is widely used to overcome the obstacle of inter-symbol interference (ISI).
Driven by the accelerating interest in cloud services, enhanced security through data-replication and growing media consumption, the popularity of 100G metro optical network is inevitable and only a matter of time.