Optical Networking Best Practices Handbook

9.1. WHO USES WDM?

WDM (either CWDM or DWDM) is commonly used for one of two purposes. The original and primary purpose of WDM technology is capacity enhancement. In this scenario, many streams of data are multiplexed onto a small number of fiber-optic cables. This dramatically increases the bandwidth carried per fiber. In an extreme case, suboceanic cabling today sometimes runs 144 channels of OC-192. At 10 Gbps per channel, the total bandwidth on each individual fiber is 1.44 Tb (i.e., 12,000,000,000,000 bits/s). Of course, in many scenarios, this level of bandwidth is unnecessary, but it is common to run several streams of gigabit Ethernet (GbE) over a single fiber pair when fiber-optic cabling starts to run out. In many cases, it is simply not cost-effective, or even possible, to deploy more fiber. In these cases, WDM technology is the only option left when the bandwidth inevitably needs a booster shot [1].

The second purpose for WDM technology came about more recently as more and more customers began to require high-speed network interconnections between facilities. This usage is commonly referred to as "wavelength services." A carrier (or utility company acting as a carrier) has the option of providing a full wavelength, point-to-point, for a customer with multiple physical locations. For example, a large corporation with two buildings on opposite ends of town may want to run a GbE connection between the facilities. The carrier can either deploy a GbE infrastructure, or ...