The evolution to the optical layer in telecommunications networks will occur in stages in different markets because the traffic types and capacity demands for each are different. Overall, the growth is predicted to be enormous (see Figure 12). This module will review each potential market, including the main drivers for deploying optical networks, and issues that might arise.

Figure 12. Optical Networks Market ($Millions)

Long-Haul Networks

Nowhere else is bandwidth devoured so quickly as in the long-haul network. Spanning for thousands of miles in many cases, long-haul networks are different from all other markets in several important regards: long spans between nodes and extremely high bandwidth requirements.

Long-haul networks were the first to have large-scale deployment of optical amplifiers and wideband–WDM systems mainly because of cost reductions. Optical amplifiers are a cheaper alternative to a large number of electrical regenerators in a span. In addition, using WDM, interexchange carriers increased the fiber capacity by using WDM, which avoids the large expenditures of installing new fiber.

Metro Interoffice (IOF) Networks

Networks in the metro interoffice (IOF) market have different needs for optical technologies. IOF networks are typically more interconnected and geographically localized. Because of the traffic patterns and distances between offices, optical rings and optical cross-connects will be required much earlier. IOF networks not only need to distribute traffic throughout a region, but also must connect to the long-haul network. As the optical network evolves, wavelength add/drop and interconnections will add the flexibility and value that IOF networks require.

Business-Access Networks

The last mile of the network to business customers has gone by many names: wide-area networks (WANs), metropolitan-area networks (MANs), and business-access networks. Regardless of the name, these networks provide businesses with connections to the telecommunications infrastructure. It is these networks where the application of optical networks is not so clear. Many more complexities arise in these networks, including variable bit-rate interfaces, different cost structures, and different capacity needs. Similar in architecture to IOF networks, business-access network sites are much closer together, so fiber amplification is not as important.

An important component for optical networks in business-access networks is the asynchronous transponder, which allows a variety of bit-rate signals to enter the optical network. Optical networks designed for the business access environment will need to incorporate lower-cost systems to be cost effective and enable true wavelength services. The challenge will be proving when and where DWDM is effective in access networks.