In this article, an overview of current issues and challenges in lightpath routing for optical networks is given. An architecture is presented in which optical switches are deployed, usually in the core, to interconnect IP routers at the edges. Lightpath routing within this architecture follows the framework of generalized multiprotocol label switching. Our discussion pays particular attention to the aspects of optical routing that differ from routing in traditional IP networks. Such aspects include physical layer constraints, wavelength continuity, the decoupling of control network topology from data network topology, explicit routing with wavelength assignment, and diversity routing for fast protection. We also present an algorithmic framework for lightpath computation, highlighting the issue of wavelength continuity and the differences between lightpath computation and traditional IP route computation.

This article considers the problem of real-time provisioning of optical channels in hybrid IP-centric DWDM-based networks. First, we present an overview of the emerging architectural alternatives for IP over optical networks, namely, the overlay, the peer, and the augmented models. Then lightpath provisioning issues are detailed for route selection, with a particular focus on the "routing and wavelength assignment" (RWA) problem. In particular, a broad overview is presented, with methodologies and associated algorithms for dynamic lightpath computation being outlined. Additionally, two broad constraint-based RWA algorithms for dynamic provisioning of the optical channels are presented and evaluated. Finally, the implications of implementing the proposed RWA schemes for the lightpath provisioning aspects for each of the three emerging IP-over-optical network interconnection models are examined.