Page 247 - Shaping smarter and more sustainable cities - Striving for sustainable development goals

Dense Wavelength Division Multiplexing (DWDM)

This is an optical multiplexing technology used to increase bandwidth over existing fiber networks.
DWDM works by combining and transmitting multiple signals simultaneously at different
wavelengths on the same fiber. The technology creates multiple virtual fibers, thus multiplying the
capacity of the physical medium.

WDM has revolutionized the cost per bit of transport. Owing to DWDM, fiber networks are capable
of carrying multiple Terabits of data per second over thousands of kilometers – at cost points
unimaginable less than a decade ago. State‐of‐the‐art DWDM systems support up to 192
wavelengths on a single pair of fiber, with each wavelength transporting up to 100Gbit/s capacity –
400Gbit/s and one Terabit/s on the horizon.

DWDM provides ultimate scalability and reach for fiber networks. Without the capacity and reach
of DWDM systems, most Web 2.0 and cloud‐computing solutions today would not be feasible.
Establishing transport connections as short as tens of kilometers to enabling nationwide and
transoceanic transport networks, DWDM is the workhorse of all the bit‐pipes keeping the data
highway alive and expanding.

Figure 22 – Optical transport to optical networking: evolution of the photonics layer

Use of DWDM allows providers to offer services such as e‐mail, video, and multimedia carried
protocol (IP) data over asynchronous transfer mode (ATM) and voice carried over SONET/SDH.
Despite the fact that these formats‐IP, ATM, and SONET/SDH‐provide unique bandwidth
management capabilities, all there can be transported over the optical layer using DWDM. This
unifying capability allows the service provider the flexibility to respond to customer demands over
one network.

Ethernet data link

In a world that is moving to a packet‐based future, Ethernet is the dominant data‐link protocol for
today's networks, supporting a multitude of communication applications. Also, Ethernet is one of
the key protocols used to interconnect routers and to carry applications in high‐speed optical
networks to backhaul access traffic.

ITU‐T's Technical Reports and Specifications 237