Two important aspects of optical networking are to ensure transmission integrity when connecting optically transparent channels in real time for protection, and the handling of dynamic demand, especially when survivability considerations are added. The prevalent approach for providing protected dynamic lightpath services is signaling intensive, database dependent, and requires on-the-fly cross-connection of standby lightwave channels to form protection paths. With two inter-related new concepts, we address concerns about on-the-fly concatenation of transparent optical channels to form protection paths and improve the scalability, and reduce database dependence and signalling intensity associated with current methods. An extension of the p-cycles concept to end-to-end path protection, in conjunction with the concept of a protected working capacity envelope for dynamic provisioning (which has no per-connection signaling for backup path establishment) yields a highly efficient network architecture in which protection paths are fully pre-cross-connected prior to failure and only the two lightpath end-nodes need to detect path failure and switch the lightpath (or its traffic) into a corresponding pre-planned path-protecting p-cycle.
As an alternative of the Shared Backup Path Protection (SBPP) method, we develop a framework for dynamic provisioning of survivable services based on the use of p-cycles to form a Protected Working Capacity Envelope (PWCE) within which dynamic provisioning of protected services is greatly simplified. Based on p-cycles, the restoration speed of rings is obtained, but with the capacity efficiency of shared-mesh networks. In addition, with PWCE, arbitrarily fast dynamic service demands can be handled with much less complexity (in terms of database dependency and state update dissemination) than under SBPP. Only a simple OSPF-topology view of non-exhausted spans in the envelope is required. If a new path can be routed through the envelope, it is protected by virtue of being routable. This is in contrast to needing a full database of network state so that the end-user can set up a shared backup protection path under SBPP. In addition, dissemination of state updates occurs only on the time-scale of the non-stationary evolution of the demand statistics, not on the time-scale of individual connections. During statistically stationary periods, there is no dissemination of state updates whatsoever with an envelope that is well matched to its load. The PWCE concept thus offers some new tradeoffs between operational simplicity and spare capacity efficiency. The main contribution of this work is the detailed implementation and simulation of test networks operating under PWCE and designed with novel envelope volume maximizing formulations.
We study the forcer concept in the context of p-cycle based networks. A simple but efficient forcer analysis method is proposed specifically for span-restorable networks in general. Besides identifying forcers, the method is also capable of exploiting extra servable working channels given an initial network spare capacity budget designed for pre-existing working capacities. We find that a large number of extra working channels can be served with no increase in the pre-planned spare capacity budget. This attribute of p-cycle protected networks can be used to enhance their ability to serve unforeseen demand patterns or provide an expanded envelope of protected working capacity within which dynamic demand is servable without blocking due to exceeding the protected working capacity limits.
We consider extensions of the most common mesh-restorable network capacity design formulation that enhance the dual-failure restorability of the designs. A significant finding is that while design for complete dual-failure restorability can require triple the spare capacity, dual failure restorability can be provided for a fairly large set of priority paths with little or no more spare capacity than required for single-failure restorability. As a reference case we first study the capacity needs under complete dual-failure restorability. This shows extremely high capacity penalties to support 100% dual-failure restorability. A second design model allows a user to specify a total capacity budget limit and obtain the highest average dual-failure restorability possible for that investment limit. A third design strategy supports multiple-restorability service class definitions at minimum total cost. Restorability can range from best-efforts-only on any failure to an assurance of complete single and dual-failure restorability, on a per-demand basis. This work shows how to economically support an added service class in the upward quality direction: assured dual failure survivability. This lets a network operator tailor the investment in capacity to provide ultra-high availability on a selective basis, while avoiding the very high investment required for complete dual-failure restorability for all.
We study the total capacity requirements of span-restorable mesh network designs as the percentage of all possible dual failure combinations incident on a common node is increased. Our interest is in questions such as: Are there any guidelines or insights as to how many such SRLGs can be sustained before the capacity penalty becomes severe? Can we diagnose which SRLGs are the most limiting to overall network efficiency? When would it be worthwhile to take physical measures to eliminate a certain SRLG? In addressing these questions we provide a design formulation and procedure for planning any span-restorable network for a known set of SRLGs. One finding of interest is that if all dual failure combinations incident to a common node are allowed for in the design, then nearly all other dual span failure combinations (any two spans in the network) will also be restorable. We also produce experimental results showing how total capacity depends on the relative number or frequency of co-incident SRLGs and quantify how the type of SRLG will impact design costs.
Conference Committee Involvement (1)
Reliability of Optical Fiber Components, Devices, Systems and Networks
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