Assessing IP vs optical restoration using the open-source Net2Plan tool

Economic sustainability of the ever-increasing traffic requirements is built on the cost reduction of IP-over-WDM backbone networks. These networks are composed of a set of IP routers connected via all-optical circuits (or lightpaths), bypassing intermediate nodes, thanks to reconfigurable optical equipment. Today, traffic survivability is ensured by over-dimensioning the IP layer and using some IP/MPLS fast convergence/reroute mechanism, without making use of the reconfigurability of the optical layer. In this paper, we provide algorithms to dimension an IP-over-WDM network under two different resilience schemes: IP restoration and optical-followed-by-IP restoration. In both cases, the IP routing is controlled by an OSPF-like algorithm. In the optical-followed-by-IP restoration, OSPF reactions to failures are delayed by appropriately setting the OSPF hold-off timer, giving time to lightpath restoration attempts to be completed. We evaluate the performance, in terms of bandwidth requirements and traffic survivability, of these two resilience schemes. Our tests show that optical-followed-by-IP restoration is a cost-efficient alternative to IP restoration, still improving traffic survivability in most cases, without any degree of over-dimensioning. Results were obtained using the open-source Net2Plan tool, and source code is available on the website.