Path vs. Cutset approaches for the design of logical survivable topologies

Abstract

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

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“…One of the earliest proposals of cut-disjoint mapping for survivable virtual optical network (VON) mapping in IP-over-WDM networks is an extension of the routing and wavelength assignment (RWA) called RWA-cut-disjoint [98], [99]. Cutdisjoint mapping technique offers a more scalable resiliency compared to path-disjoint approaches introduced in other studies such as [124]. Given that RWA-cut-disjoint enforces nearfull VON survivability against single-physical-link failures and a best-effort resiliency for dual-link failures, the survivable virtual topology routing (SVTR) is also suggested in [100] to deal with larger failures (i.e., a group of links and/or nodes which might fail together, a so-called shared-risk group (SRG)).…”

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“…The survivable mapping constraint guarantees a survivable CN mapping for any single physical-link failure by enforcing cut-disjoint mapping as studied in [21][22][23]. This constraint ensures that virtual links of the same cut (i.e., set of links whose simultaneous failures disconnects the virtual topology) do not share the same physical link.…”

“…Ref. [23] showed the advantage of cut-disjoint approach over path-disjoint approach to provide protection in VN.…”

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