The business case for embedded DWDM over active DWDM systems
Several methods are available for data center interconnect and for connecting traffic between sites in a distributed data center. Companies can run the network by themselves in a private network or have an operator run it for them through a managed service. Building a private network requires access to fiber, either owned or leased, between the sites. Various technology choices are possible depending on the total amount of traffic required throughout the lifetime of the network and the distance between sites. This article focuses on comparing two of them: embedded DWDM and active DWDM systems.
Active DWDM systems
An active DWDM system, commonly referred to as a transponder-based system, offers a way to transport large amounts of data between sites in a data center interconnect setting. The transponder takes the outputs of the SAN or IP switch format — usually in a short wave 850nm or long wave 1310nm format — and converts them through an optical-electrical-optical (OEO) DWDM conversion.
There is a clear demarcation point between the optical DWDM layer and the data layer (Ethernet or Fibre Channel protocols). This is important for two reasons. First, a DWDM signal can travel farther than a short-range signal, making it possible to connect geographically separated data centers. Second, many DWDM signals can be connected through a multiplexer and simultaneously transmitted over a dark fiber. But even though these systems can transport huge amounts of data, they are more suited to telecom operators and tend to be overly complicated for data center interconnect purposes for corporations.
Embedded DWDM is able to transport the same number of traffic channels over a dark fiber as a standalone DWDM system, but in a much simpler way with fewer components. Instead of having the OEO conversion from short range to DWDM, the transponder is eliminated because the DWDM transceiver is connected directly in to the SAN or IP switch. From here an LC patch cable connects it to a passive multiplexer (a 1U fiber termination unit), which gathers the traffic signals together and transports them simultaneously over a single dark fiber link.