PDF of this tutorialAside from the enormous capacity gained through optical networking, the optical layer provides the only means for carriers to integrate the diverse technologies of their existing networks into one physical infrastructure. DWDM systems are bit-rate and format independent and can accept any combination of interface rates (e.g., synchronous, asynchronous, OC–3, –12, –48, or –192) on the same fiber at the same time. If a carrier operates both ATM and SONET networks, the ATM signal does not have to be multiplexed up to the SONET rate to be carried on the DWDM network. Because the optical layer carries signals without any additional multiplexing, carriers can quickly introduce ATM or IP without deploying an overlay network. An important benefit of optical networking is that it enables any type of cargo to be carried on the highway.
But DWDM is just the first step on the road to full optical networking and the realization of the optical layer. The concept of an all-optical network implies that the service provider will have optical access to traffic at various nodes in the network, much like the SONET layer for SONET traffic. Optical wavelength add/drop (OWAD) offers that capability, where wavelengths are added or dropped to or from a fiber, without requiring a SONET terminal. But ultimate bandwidth management flexibility will come with a cross-connect capability on the optical layer. Combined with OWAD and DWDM, the optical cross-connect (OXC) will offer service providers the ability to create a flexible, high-capacity, efficient optical network with full optical bandwidth management. These technologies are today's reality: DWDM has been utilized in the long-distance network since 1995, OWAD will be available in products in 1998, and the first OXC was showcased at industry conventions in 1997.
