Robust network design for IP/optical backbones

Recently, Internet service providers (ISPs) have gained increased flexibility in how they configure their in-ground optical fiber into an IP network. This greater control has been made possible by improvements in optical switching technology, along with advances in software control. Traditionally, at network design time, each IP link was assigned a fixed optical path and bandwidth. Now modern colorless and directionless reconfigurable optical add/drop multiplexers (CD ROADMs) allow a remote controller to remap the IP topology to the optical underlay on the fly. Consequently, ISPs face new opportunities and challenges in the design and operation of their backbone networks [IEEE Commun. Mag.54, 129 (2016); presentation at the International Conference on Computing, Networking, and Communications, 2017; J. Opt. Commun. Netw.10, D52 (2018); Optical Fiber Communication Conference and Exposition (2018), paper Tu3H.2]. Specifically, ISPs must determine how best to design their networks to take advantage of new capabilities; they need an automated way to generate the least expensive network design that still delivers all offered traffic, even in the presence of equipment failures. This problem is difficult because of the physical constraints governing the placement of optical regenerators, a piece of optical equipment necessary to maintain an optical signal over long stretches of fiber. As a solution, we present an integer linear program (ILP) that does three specific things: It solves the equipment placement problem in network design; determines the optimal mapping of IP links to the optical infrastructure for any given failure scenario; and determines how best to route the offered traffic over the IP topology. To scale to larger networks, we also describe an efficient heuristic that finds nearly optimal network designs in a fraction of the time. Further, in our experiments our ILP offers cost savings of up to 29% compared to traditional network design techniques.