Logical topology design for IP rerouting: ASONs versus static OTNs

IP-based backbone networks are gradually moving to a network model consisting of high-speed routers that are flexibly interconnected by a mesh of light paths set up by an optical transport network that consists of wavelength division multiplexing (WDM) links and optical cross-connects. In such a model, the generalized MPLS protocol suite could provide the IP centric control plane component that will be used to deliver rapid and dynamic circuit provisioning of end-to-end optical light paths between the routers. This is called an automatic switched optical (transport) network (ASON). An ASON enables reconfiguration of the logical IP topology by setting up and tearing down light paths. This allows to up- or downgrade link capacities during a router failure to the capacities needed by the new routing of the affected traffic. Such survivability against (single) IP router failures is cost-effective, as capacity to the IP layer can be provided flexibly when necessary. We present and investigate a logical topology optimization problem that minimizes the total amount or cost of the needed resources (interfaces, wavelengths, WDM line-systems, amplifiers, etc.) in both the IP and the optical layer. A novel optimization aspect in this problem is the possibility, as a result of the ASON, to reuse the physical resources (like interface cards and WDM line-systems) over the different network states (the failure-free and all the router failure scenarios). We devised a simple optimization strategy to investigate the cost of the ASON approach and compare it with other schemes that survive single router failures

Influence of the IP traffic asymmetry on the cost of the optical network layer

The main traffic to be carried by a backbone network in the future (or even now) will be (is) IP traffic, which is unidirectional and asymmetric in nature. Today, most backbone networks are still designed for bidirectional, symmetrical services like SDH/SONET. In the future, the transmission links in the optical layer will probably still be symmetric (same amount of capacity installed in both directions of the optical link), and operators will probably continue to lease bidirectional capacity to their customers. However, the traffic that will be conveyed over those bidirectional transmission links will be mainly unidirectional and asymmetric. This paper studies the influence of the asymmetric nature of IP traffic on the underlying optical layer. In case the optical layer contains bidirectional symmetric capacity (as is almost always the case nowadays), it shows how cost(in)efficient this optical capacity is used for IP traffic patterns with varying asymmetry. The comparison is also made with a unidirectional optical layer, in which the capacity (line-systems) installed in the network is asymmetric (more capacity can be present in one direction of an optical link than in the other direction), or in which the capacity that is leased by operators is asymmetric (e.g., an ISP can choose to lease two wavelengths from city A to city B and five wavelengths in the other direction, from city B to city A)