Working Capacity Envelope Research Articles

Dynamic p-Cycle Protection in Spectrum-Sliced Elastic Optical Networks

We investigate dynamic pre-configured-cycle (p-cycle) protection design for spectrum-sliced elastic optical networks (EONs). Several novel algorithms are proposed to use the spectrum planning of working and backup resources. We first combine the protected working capacity envelope (PWCE) p-cycle design with spectrum planning, and design an algorithm that can achieve dynamic p-cycle design in EONs. Then, to resolve the coverage issue of the PWCE-p-cycles, we consider dynamic p -cycle design with Hamiltonian cycles and propose to use topology partition for reducing the lengths of backup paths. Simulation results show that our proposed algorithms achieve lower blocking probability than the shared path-protection (SPP) algorithm, while the average length of backup paths per request can be controlled well. To the best of our knowledge, this is the first attempt to address dynamic p-cycle protection design with spectrum planning for EONs.

An efficient column generation design method of p-cycle-based protected working capacity envelope

The protected working capacity envelope (PWCE) concept was proposed by Grover (2004) in order to simplify network operations and management in survivable wavelength division multiplexing (WDM) networks. In this paper, we focus on the design of PCWE and investigate a new design method based on column generation (CG) for designing survivable WDM networks based on p-cycle PWCE. Proposed design algorithms for PWCE and p-cycle proceed in two steps: A first step where a large (sometimes huge) number of cycles is enumerated followed by a second step where the selection of the most promising p-cycles is made with the help of combinatorial optimization tools. In this paper, we develop a new (single-step) method based on large scale optimization tools, that is, CG techniques, where the generation of cycles is dynamic and embedded within the optimization process. The key advantage of CG techniques is that no a priori cycle enumeration step is required ahead of the optimization process: The generation of the relevant cycles, only one or few at a time, is embedded in the optimization process. We conducted intensive computational experiments to compare the performances of our CG algorithms with four other algorithms in the literature. The different algorithms were compared with regard to several design metrics and running time. Results obtained in the experiments on five different network instances show that the CG-based algorithm outperforms by far all proposed algorithms in the literature, both with respect to the scalability (much smaller computing times for large network instances) and also with respect to the quality of the solutions.

PWCE design with Hop-Limited p-Cycles for dynamical protection provision in WDM networks

In future high-capacity wavelength division multiplexed (WDM) optical networks; the failure of a network component such as a fiber link can lead to severe disruption in the networks' traffic. Hence, it is imperatively important to provide fast and 100% protection in WDM optical networks. In this paper, a Hop-Limited p-Cycle-based approach is employed for protected working capacity envelope (PWCE) design. The results reveal the cycle hop not only affects the total protected working units but also the blocking probability performance.

P-Cycle protection at the glass fiber level

The cost and complexity of wavelength assignment, wavelength conversion and wavelength-selective switching are always of primary considerations in the design of survivable optical networks. This proposal recognizes that as long as the loss budgets are adequate, entire DWDM wavebands could be restored with no switching or manipulation of individual lightpaths; so that the DWDM layer would never know the break happened. And environments where fiber switching devices are low cost, and ducts are full of dark fibers provide a very low cost alternative to protect an entire DWDM transport layer (or working capacity envelope) against the single largest cause of outage. Yet, while nodes and single DWDM channels may fail, a pre-dominant source of unavailability is the physical damage of optical cables. Thus, with the objectives of reducing the overall real CapEx costs and removing the complexity due to wavelength assignment and wavelength continuity constraints when configuring p-cycles in a fully transparent network context, this paper addresses the subsequent questions: if it is ultimately glass that fails, what if just the glass is directly replaced? More specifically, what if p-cycles were used to rapidly, simply and efficiently provide for the direct replacement of failed fiber sections with whole replacement fibers?

Near optimal routing and capacity management for PWCE-based survivable WDM networks

Protected Working Capacity Envelope (PWCE) has been proposed to simplify resource management and traffic control for survivable WDM networks. In a PWCE-based network, part of the link capacity is reserved for accommodating working routes, and the remaining capacity is reserved for backup routes. The shortest path routing is applied in PWCE-based networks. An arrival call is accepted only when each link along the shortest path has a free working channel. Such a working path routing scheme greatly simplifies the call admission control process for dynamic traffic, and it is especially suitable for implementation in a distributed manner among network nodes. In this article, we investigate two protection strategies: Bundle Protection (BP) and Individual Protection (IDP). In BP, only one backup path can be used to protect a failure component, whereas multiple backup paths can be used in IDP. We formulate four mixed integer non-linear programming (MINLP) problems using BP and IDP strategies for single link and single node failure protection. Each model is designed to determine link metrics for shortest working path routing, working and backup channel assignments, and backup path planning. Our objective is to minimize call-blocking probability on the bottleneck link. Since these models are highly non-linear and non-convex, it is difficult to obtain exact global optimal solutions. We propose a Simulated Annealing-based Heuristic (SAH) algorithm to obtain near optimal solutions. This SAH adopts the concepts of simulated annealing as well as the bi-section technique to minimize call-blocking probabilities. To evaluate the performance, we made simulation comparisons between SAH and the unity link weight assignment scheme. The results indicate that SAH can greatly reduce call-blocking probabilities on benchmark and the randomly generated networks.

Performance evaluation of p-cycle based protection methods for provisioning of dynamic multicast sessions in mesh WDM networks

Network survivability is crucial to both unicast and multicast traffic. Up to now, extensive research has been done on unicast traffic protection. Recently, due to the rapid growth of multicast applications, such as video-conferencing, high definition television (HDTV), distance learning, and multi-player on-line gaming, the problem of multicast traffic protection has started to draw more research interests. The preconfigured protection cycle (p-cycle) method proposed by Grover offers fast speed in restoration (because p-cycles are pre-cross-connected) and high efficiency in resource utilization (because p-cycles protect both on-cycle and straddling links). So far p-cycles based protection approaches have been intensively studied for unicast traffic protection, but have been rarely investigated for multicast traffic. We propose to apply p-cycles to dynamic protection provisioning of multicast traffic, and evaluate the blocking performance in comparison to other existing multicast protection schemes. We consider three different p-cycle based multicasting protection methods, namely dynamic p-cycle (DpC) design, p-cycle based protected working capacity envelope (PWCE) design, and hybrid DpC and PWCE design. We show that p-cycle-based multicast protection approaches offer much better blocking performance, as compared with other existing multicast protection schemes. The main reasons for the much better blocking performance are attributed to the facts that (i) the selection of p-cycles is independent of the routing of the multicast light trees, (ii) there are no path/segment disjoint constraints between the selected p-cycles and the multicast light trees to be protected, (iii) the selected p-cycles are the most efficient p-cycles.

Dynamically survivable WDM network design with p-cycle-based PWCE

The concept of a protected working capacity envelope (PWCE) is very attractive for designing a dynamically survivable WDM network. We consider a p-cycle-based PWCE approach for designing survivable WDM networks where the traffic demand is dynamically changing. We develop an integer linear programming formulation to determine the protected working capacity envelope and use simulations to evaluate the blocking performance for different network models.

Design and performance of protected working capacity envelopes based on p-cycles for dynamic provisioning of survivable services

As an alternative to the shared backup path protection (SBPP) method, we develop a framework for dynamic provisioning of survivable services through the use of p-cycles to form a protected working capacity envelope (PWCE) within which dynamic provisioning of protected services is greatly simplified. With a PWCE, arbitrarily fast dynamic service demands can be handled with much less complexity (in terms of database maintenance and state update dissemination) than with SBPP. Only a simple open-shortest-path-first (OSPF) topology view of nonexhausted 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 the network state so that the end user can set up a shared backup protection path under SBPP. In addition, dissemination of spare capacity sharing updates occurs only on the time scale of the nonstationary evolution of the demand statistics, not like SBPP, which occurs on the time scale of individual connection arrivals or departures. During statistically stationary periods there is no dissemination of spare capacity sharing updates whatsoever with an envelope that is well matched to its load. The PWCE concept thus offers some new trade-offs between operational simplicity and spare capacity efficiency. Under the PWCE concept p-cycles are of particular interest for consideration because, although many protection techniques can be the basis of PWCE operation p-cycles offer the unique combination of ring-like protection times with the capacity efficiency of shared-mesh networks. But, in addition, p-cycles offer a further important property for a transparent optical network: that of providing fully pre-cross-connected protection paths. Because all protection paths are preconnected structures, optical transmission path integrity can be validated before failure and is not of such concern as it is in schemes where optical replacement path segments of several wavelength channels would have to be assembled on the fly (without the benefit of o-e-o between stages). 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. A wide range of network capacity environments were considered to find that p-cycle-based PWCE is close to SBPP in blocking performance while simultaneously offering much simpler operation and a faster restoration speed.

The protected working capacity envelope concept: an alternate paradigm for automated service provisioning

At present we see only one basic approach being considered by implementors and standards organizations for provisioning of dynamic protected lightpath services that make efficient use of shared protection capacity. This is the paradigm of a primary working path protected end-to-end by a disjoint backup path using shared spare capacity. Sharing is arranged among the backup paths associated with other primary paths that are failure-disjoint from the current primary path. This approach called shared backup path protection (SBPP) has many advantages but also provides a great deal of network state information to be available and current in every node. It also makes the arrangement of protection a per-connection task, rather than user-selectable service option supported by the network itself. We propose an alternative paradigm for consideration, partly summed up as provisioning over protected capacity rather than provisioning protection. Under a given distribution of spare capacity, locally acting protection or restoration schemes create an "envelope" of protected working channels. Dynamic provisioning within this envelope is simplified to a shortest path routing problem and (depending on the mode of operation) requires little or no dissemination of state changes on a per-connection basis. We explain how existing "static" capacity design methods can be adopted to the dimensioning of such a working capacity envelope and the envelope dimensions further adapted online to track evolution of the overall pattern of random demand. An important property is that nothing needs to be done to arrange protection for services on the per-connection timescale other than routing the service itself. Arbitrarily fast-paced demand arrivals and departures can be accommodated within a static distribution of spare capacity. Adjustments to the envelope itself are required only on the timescale on which the statistical parameters of the random demand changes. This may provide an inherently more scalable, less database-dependent, and higher-availability alternative than SBPP, or at least an additional service modality that can be offered to customers.