In today’s WDM all-optical networks, a majority of existing virtual topology design algorithms have ignored link-performance limiting factors such as dispersion, amplified spontaneous emission (ASE), cross talk resulting from signal leakage in optical cross connects (OXCs), and fiber nonlinearities. All these factors result in bit-error-rate (BER) degradation at the receiving end. To maintain a BER below a certain level, some lightpaths in the network will require regeneration at the intermediate nodes, thus, setting up a lightpath in a multihop manner. In synchronous optical network (SONET) ring networks, the terminal equipment cost associated with electronic multiplexing is predominantly high. Wavelength add–drop multiplexers reduce the amount of SONET terminal equipment at each node by allowing certain wavelengths or bands to bypass the node optically without being electronically terminated. Most of the previous research in this area has focused on the virtual topology design and wavelength-routing algorithms to address the cost savings. Here we consider both unidirectional path-switched and bidirectional line-switched rings (UPSR, BLSR/2) with optical bypass. We analytically derive a relationship for the number of regenerators to support both single-hub and all-to-all situations for uniform and nonuniform traffic cases with an arbitrary internodal length distribution. We obtain lower and upper bounds for regeneration cost on a ring when nodes are randomly placed. Equivalency is established between UPSR and BLSR/2 networks in terms of regeneration cost for cases of single link failure. Regeneration cost advantage is shown for nonzero dispersion-shifted fiber (NZDSF) over standard single-mode fiber in dispersion-limited regimes.
© 2003 Optical Society of AmericaPDF Article