Metropolitan DWDM: A dynamically configurable ring for the KomNet field trial in Berlin

We present the system concept of a dynamically configurable all-optical add /drop multiplexer for metropolitan wavelength division multiplex rings usin g dense channel spacing (DWDM). We first outline the essential network requ irements. Subsequently, an optical system concept is presented that meets t hese requirements. In the network elements, innovative all-optical switchin g technology is employed. Tunable fiber Bragg gratings that perform routing functions by wavelength filtering are discussed in more detail. The system is laboratory-tested. Recently, it has been installed in Berlin for a mult i-vendor field trial within the German research program "KomNet." Three opt ical add/drop multiplexers form a dynamically configurable Metro DWDM ring. Future communication networks will face three major changes: A strong increase in traffic flow, mainly driven by Internet applications. The merging of telecommunication and data networks. Switching granularities getting coarser corresponding to an increase in bit rates of single data streams. At the same time the requirements for reliability and availability will rem ain high and pressure will increase to operate networks cost-efficiently. T hese requirements can hardly be met alone by the currently deployed synchro nous network technology (SONET/SDH) in a cost-efficient manner. In many networks that provide path lengths up to 300 km, DWDM solutions are ideally suited for this new situation [1], Metro DWDM accommodates high ba ndwidths: a metropolitan ring that provides 0.8 terabit/s ring capacity has been demonstrated recently [2]. Furthermore, Metro DWDM can provide optica lly transparent channels enabling the transport of various data formats sim ultaneously, e.g., SONET/SDH and Gigabit Ethernet. Conversion to a standard format becomes obsolete. A third benefit is the granularity at wavelength channel level. It is bette r suited for future network demands than the fine granularity that SONET/SD H network elements provide. Low-rate streams requiring fine switching granu larities are losing importance. Metro DWDM networks can be a viable solution if new fiber installation is t oo expensive or impossible. This is known from long-haul systems and can ap ply in some city or regional networks as well. To reduce operational costs, automatic switching of DWDM channels can be pe rformed by remote control (dynamic configuration). This requires optical sw itching matrices or alternative techniques that can be controlled electroni cally. However, dynamic configuration causes higher installation costs. Man ual configuration of DWDM channels is less expensive. It is performed by ha nd-plugging cables to optical connector patch boards (distribution frames). The cost-efficiency of dynamic configuration depends on the average lifeti mes of the optical connections. The all-optical add/drop multiplexer (OADM) presented in this article provides both manual and dynamic configuration. In this article, the system concept of the OADM is developed starting with basic metropolitan DWDM network requirements. These requirements are treate d in the first two sections. The next section describes the features of the DWDM ring, followed by a presentation of the system concept of the flexibl e OADM. Our focus is on dynamic configuration techniques. Since tunable fib er Bragg gratings are promising components for dynamic optical channel swit ching [3], this technology is treated in more detail in the last section.