# Robust Network Design for Software-Defined IP/Optical Backbones

## TL;DR

This paper introduces an ILP-based method and a heuristic for designing cost-effective, resilient SDN-enabled IP/optical backbones, optimizing equipment placement, optical mapping, and traffic routing under failure scenarios.

## Contribution

It presents a novel ILP formulation and a scalable heuristic for integrated network design, considering optical equipment placement and failure resilience in SDN-enabled optical networks.

## Key findings

- ILP achieves up to 29% cost savings over traditional methods.
- Heuristic provides near-optimal solutions faster for larger networks.
- The approach effectively handles equipment placement and failure scenarios.

## Abstract

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 (i) the maturation of software defined networking (SDN), and (ii) improvements in optical switching technology. Whereas traditionally, at network design time, each IP link was assigned a fixed optical path and bandwidth, modern colorless and directionless Reconfigurable Optical Add/Drop Multiplexers (CD ROADMs) allow a remote SDN 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. Specifically, ISPs must determine how best to design their networks to take advantage of the 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 for maintaining an optical signal over long stretches of fiber. As a solution, we present an integer linear program (ILP) which (1) solves the equipment-placement network design problem; (2) determines the optimal mapping of IP links to the optical infrastructure for any given failure scenario; and (3) 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.