FIGURE 3.1 Traffic In bytes per second (B/s) (1 byte = 8 bits) on the Internet, on voice telephone, and overall, 1986-2007. Also shown is the capacity to compute in general-purpose machines, expressed in millions of instructions per second (MIPS). SOURCE: MIPS graph based on data extracted from Hilbert, M., and P. Lopez. 2011. The world’s technological capacity to store, communicate, and compute information. Science 332(6025):60-65.

from one fiber route to another fiber route directly in the optical domain without the need for conversion to electronics—are now heavily deployed in long-haul terrestrial networks as well as metropolitan networks. Wavelength-routed networks provide cost-effective solutions because they allow data on wavelengths passing through a node at a multi-route network node to remain in the optical domain and benefit from the cost-effective multi-wavelength amplification enabled by optical amplifiers, rather than needing to be individually electronically regenerated. The large increase in capacity demand has ensured that a prerequisite for the economic viability of such networks—namely, that the capacity demand between any two node pairs on the network be at least as large as that which can be carried by a single wavelength—is met.

WDM optical networks require reconfigurable optical add/drop multiplexers (ROADMs) to, under network electrical control, drop or add wavelength channels at a node and to switch wavelength channels from one fiber route to another. ROADMs are key enablers that have evolved significantly in their functionality, providing increasing levels of flexibility, and in their capacity, or number of fiber ports and wavelengths per fiber, over the last decade. Further progress in these network elements and their enabling technologies will be essential to addressing the growing demand for capacity.

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