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Carrier Networking Optical Networking
5 minute read

Optical Data Center Interconnect: Connecting Your Data Centers With Private DWDM Technology

Optical Data Center Interconnect (DCI) provides a cost saving, high density, flexible alternative to leased circuits for connecting geographically separated data centers.

In This Article

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Overview

Optical Data Center Interconnect (DCI) is a widely deployed architecture that provides high-density, layer 1 connectivity between two physically disperse locations. Traditionally, enterprise network operators lease these services from various service providers, paying a monthly recurring fee based on the size and quantity of circuits. Though leased circuits have their benefits, deploying your own DCI network has become a popular option amongst network operators of all sizes. Cost savings, the flexibility of bandwidth growth, security and operational control are some of the reasons driving operators to deploy their own optical DCI network. 

Optical DCI systems, powered by advanced DWDM optics and amplifier technology, enable connectivity between data centers as close as 1 Km or as far as 1000+ Km apart. DWDM equipment is located at each data center and interconnected with fiber optic cables spanning between each data center. The fiber optic links between the data centers are known as "dark fiber." Dark fiber has no equipment or services attached; imagine a very long patch cord running underground between the data centers. Unlike a "lit" fiber-optic service where you can lease wavelengths from a provider, dark fiber enables you to connect your own DWDM equipment providing up to 96 DWDM channels for you to use as needed.

Connecting data centers with DWDM technology isn't a new concept but traditionally it only made financial sense for large data center environments. This was due to the system's cost, size and power requirements; you needed significant bandwidth demands to realize the cost savings. Within the past five years, that has all changed. 

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As cloud provider networks began to grow exponentially, the pressure for equipment manufacturers to create smaller, faster and cheaper network components increased. This ushered in a new concept in the DWDM device form factor, the "pizza box." The pizza box system did away with the traditional chassis and line card systems. It's a physically small, self-contained system — picture a small data center switch, 1 or 2 RU (1.5"-3") in height. Innovations in optics technology led to smaller components with lower power requirements. In parallel, advancements in the processors that process the optical signals resulted in smaller, lower power and higher density systems. Further component development has decreased power and size to enable 400G DWDM pluggable optics. These pluggable optics can be seated directly in a router or switch, eliminating the need for the pizza box device in certain applications. 

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A closer look

Optical DCI networks, also known as point-to-point, utilize a multiplexer/demultiplexer at each site connected by the fiber optic cable between the sites. The multiplexer takes in (adds) the individual transponders wavelengths, combines them and transmits them to the other site on one fiber. On the other fiber, the demultiplexer receives wavelengths from the other site and separates (drops) them back out. Working together, this provides up to 96 bidirectional, individual connections or circuits between the two sites, the equivalent of 192 individual fibers.

The image below illustrates a point-to-point network. Routers, switches, servers, etc., connect to the transponders. The transponders connect to the multiplexer and demultiplexer. Typically, each site has an amplifier that increases the optical signal enabling it to reach longer distances. Then the amplifiers connect to the fiber between the data centers. All of this fits into a tiny footprint within the data center; an average system occupies six to eight rack units (~7" – 12"). 

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The transponder is the device that takes the electrical data stream from the routers/switches/servers and converts it to an optical signal at a specific wavelength. There are two transponder options, an independent device like the Cisco NCS-1000 series  and the Infinera GX series or a pluggable optic that sits directly in a router or switch. An independent transponder provides high density 10G, 100G and 400G Ethernet connections between data centers utilizing one or more optical wavelengths. Independent transponders are typically used when you do not own or manage the routers, switches or servers connected across the point-to-point link. They are also used when very high density and multi-rate services are required. 

If you own or manage the devices connected by your point-to-point optical system, pluggable DWDM optics are an excellent option. They eliminate the need to purchase and manage an independent transponder because that function resides within the pluggable optic seated in the router or switch. 100G, 200G and 400G DWDM data rates are available per pluggable optic, providing flexible data rate options and a straightforward "pay as you grow" model. 

Other options include fiber path protection and optical line monitoring. Fiber path protection utilizes two pairs of fiber between the data centers; if one pair fails, the system seamlessly switches to the standby pair. Optical line monitoring detects if the fiber has been damaged or cut and locates where the damage has occurred. Optical DCI networks are also very straightforward to deploy and manage due to the relative simplicity of the equipment and architecture. 

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Conclusion

Optical DCI networks provide high bandwidth, fast scaling and cost-saving solutions for multi-site data center environments. WWT has a team of Technical Solutions Architects that can help assess your needs and design the right system for you. Please reach out to our experts or contact your local WWT account team to continue the conversation.