The business case for embedded DWDM over ELWL

Several methods are available for connecting data center infrastructure at different sites in an enterprise network. 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: an eight-channel 16G FC embedded DWDM and an eight single-channel extended long wavelength (ELWL) solution.

Single-channel connectivity

Single-channel connectivity, ELWL, means that a single channel of traffic is run over a single dark fiber connection. Here, the ELWL optical transceiver is connected in to the host switch (Ethernet or Fibre Channel) at each site. The line fiber — the dark fiber that is connected between the sites — then connects directly in to the transceiver, creating an end-to-end connection between the data center infrastructure at each site. It’s a simple solution, but one that contains some fundamental flaws.

• ELWL is typically limited to 10km by the OEM vendors.
• The fiber asset is unable to be used for any other data traffic.
• Operating expense (opex) for multiple fiber leases increases linearly per channel.

Embedded DWDM

Embedded DWDM features the simplicity of the ELWL approach but with the benefit of being able to transport many traffic signals over a single dark fiber. The ELWL transceiver is replaced by a DWDM transceiver that is connected directly in to the host switch. Instead of being connected on to the line fiber, the DWDM signals are connected by an LC patch cable to a passive multiplexer. As the signals are multiplexed, they are gathered and transported together over a single dark fiber link, providing a much more efficient solution for connecting, for example, data center infrastructure at different sites.

Assumptions

Each individual ELWL circuit is based on a fiber rental of $1000/month and $2000 per pair of OEM-approved ELWL transceivers.

The embedded DWDM platform is based on a fiber rental cost of $1000/month and $68K for an 8-channel system.

The clear benefits of dark fiber and embedded DWDM

Using individual ELWL single-channel transceivers is simple and convenient, but there are hidden costs and limitations. Usually, single-channel transceivers approved by the OEM vendors have a limitation of 10km or so. By simply replacing the ELWL transceiver with a DWDM transceiver when connecting your data center infrastructure, you’ll gain several key benefits:

• The distance between sites, even for a single channel, increases from 10km to 40km (200km if an intelligent M-Series multiplexer is used).
• By connecting the DWDM transceivers to a passive multiplexer (think of a multiplexer as a 1U fiber patch panel that doesn’t require power), up to 80 traffic channels can be connected over the same pair of fibers.
• You can add new channels to an existing embedded WDM system simply by adding new transceivers (either 16/8G Fibre Channel or 10/1G Ethernet), and the circuits are up and running immediately. No waiting for new fiber connections to come on line.
• The capex of an ELWL circuit is only lower than an embedded DWDM system for a single channel (multiplexers are not used with ELWL transceivers). As soon as an additional channel is required, you will achieve savings by using a multiplexer to exploit the potential of a dark fiber connection.