Multi-layer optical networks have recently evolved towards IP-over-WDM networks. Therein, in order to avoid protection/restoration redundancies against either single or multiple failures, synergies need to be developed between IP and optical layers in order to reduce the costs and the energy consumption of the future IP-over-WDM networks.We propose two new optimization models. The first one is an enhanced cutset model, relying on a column generation reformulation. The second one is a path model, based on a multiflow formulation. Both models can solve exactly most benchmark instances, which were only solved heuristically so far. I. INTRODUCTIONThe design and the management of the future networks will rely on an all IP-design, where synergies will need to be developed between the IP and the optical layers in order to reduce the energy consumption and the network costs, as well as to guarantee the Service Level Agreements (SLA) while bandwidth greedy applications, like video services and IPTV services, will continue to grow.Network failures, such as link or node failures, cannot be fully avoided when it comes to network management. Consequently, a backup mechanism needs to be used to ensure the network connectivity. When a failure occurs, the backup mechanism establishes an alternative path to carry the interrupted connections. Depending on whether this alternative path is generated online or offline, the corresponding backup mechanism is referred to as restoration or protection, respectively. In multi-layer networks, failures, whether single or multiple ones, have been traditionally taken care by the layer in which they appear, throughout restoration mechanisms in the IP layer and protection or restoration ones in the optical layer. In order to enhance the efficiency of the future networks, with respect to costs, energy consumption and quality of service, cross-layer protection/restoration is now more often envisionedThe IP layer is referred to as the logical/virtual layer where each logical link is mapped to a lightpath (i.e., a direct optical connection without any intermediate electronics) in the optical/physical layer. A single duct failure in an optical network can result in several broken physical links, and consequently in several disrupted logical links, and in a disconnected logical topology. Hence, a first condition for the existence of a survivable logical topology is to remain connected (survivable) in case of any network failure [3], and then to make sure enough bandwidth is available in order to ensure successful IP restorations. However, synergies need to be developed in
We study the design of logical survivable topologies for service protection against single or multiple failures in IPover-WDM networks where protection can be provided either at the optical layer, or at the network (IP) layer. Indeed, synergies need to be developed between IP and optical layers in order to optimize the resource utilization and to reduce the costs and the energy consumption of the future networks.We propose a new optimization model, an enhanced cutset model, which relies on a column generation reformulation for the design of a survivable logical topology. It is a highly scalable model and it makes possible the (near) exact solution of several benchmark instances, which were only solved with the help of heuristics so far. In addition, much larger instances than in previous studies can be solved as the proposed formulation avoids the explicit or implicit enumeration of cutsets. In the numerical experiments, we explore how survivability evolves when the number of failure sets increases. I. INTRODUCTIONThe design and the management of the future networks will rely on an all IP-design [1], [2], where more synergies will need to be developed between the IP and the optical layers in order to optimize the resource utilization, to reduce the energy consumption and the network costs, and to guarantee the Service Level Agreements (SLA) while bandwidth intensive applications, like video or IPTV services and on-line gaming, will continue to emerge [3].The example in Figure 1 illustrates a resiliency benefit of a synergy between the IP and the optical layers. Logical links are indicated by plain blue directional arrows, while optical spans are represented by black undirected lines, and mappings of logical links onto the physical topology are represented by dotted lines. Upon a failure of the physical span between the optical cross connect OXC 3 and OXC 2 , both logical links ℓ 1 from router R 3 to R 2 and ℓ 2 from router R 5 to R 4 are disrupted. Indeed, both logical links have a mapping using the same physical span between OXC 2 and OXC 3 . However, if the mapping of ℓ 2 = (R 5 , R 4 ) is changed from (OXC 4 /R 5 , OXC 2 , OXC 3 , OXC 5 /R 4 ) to (OXC 4 /R 5 , OXC 6 , OXC 5 /R 4 ), then the logical topology can survive to a failure on span (OXC 2 , OXC 3 ).Network failures, such as link or node failures, whether at the IP or optical layers, cannot be fully avoided. Consequently, a backup mechanism needs to be used. When a failure occurs, the backup mechanism establishes an alternative lightpath to carry the interrupted connections. Depending on whether this alternative lightpath is generated online or offline, the
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