Optimal Integer Linear Programming Formulation Research Articles

Joint content placement and lightpath routing and spectrum assignment in CDNs over elastic optical network scenarios

In this work, we address the problem of jointly deciding the placement of the contents delivered by a Content Distribution Network (CDN) among the available data centers, together with the allocation of the lightpaths required to serve the anycast demands initiated by the CDN network users, assuming an underlying high-capacity Elastic Optical Network (EON). We firstly present an Integer Linear Programming (ILP) formulation to optimally solve the targeted problem. This ILP formulation is of high complexity, though, and cannot be used to solve realistically sized problem instances. Hence, we also introduce a novel heuristic called CPRMSA-PD, which decomposes the problem into three sub-problems and applies greedy heuristics and simulated annealing meta-heuristic techniques to yield accurate solutions with practical execution times. We validate the performance of our CPRMSA-PD heuristic in medium-sized problem instances by comparing its results to the ones of the optimal ILP formulation. Next, we use it to give extensive insights into the effects of different key parameters identified in large CDN over EON backbone networks.

Bandwidth-variable optical transport network with adjustable time-modulated and inverse-multiplexed wavelength channels

This paper presents a bandwidth-variable and optical-groomable (BVOG) transport network architecture based on time-modulated optical cross-connects that enables efficient switching of periodic burst-sequenced traffic in addition to wavelength streaming traffic; with an elastic control plane that shapes each sub-wavelength traffic stream at the network edge into a sequence of periodic bursts, and inverse-multiplexes a supra-wavelength traffic stream into a group of multiple wavelength traffic streams and a potential sub-wavelength traffic stream to match the bandwidth requirement. BVOG network enables variable-time-slotted lightpaths with variable-length time slots to meet the bandwidth requirements of sub-wavelength traffic; and inverse-multiplexed lightpath-group (IM-lightpath-group) with variable group size to meet the bandwidth requirements of supra-wavelength traffic. For the problem of "routing and wavelength and time assignment" (RWTA) for sub-wavelength traffic; this paper presents an optimal integer linear programming (ILP) formulation that maximizes total network throughput, and a heuristic algorithm to minimize the blocking probability of future connection requests. For the problem of "inverse-multiplexed routing and wavelength assignment" (IMRWA) for supra-wavelength traffic; this paper presents an optimal ILP formulation that minimizes the total number of hops and the total per-hop propagation delays of the IM-lightpath-group, and a heuristic algorithm that minimizes the total number of wavelength channels of the IM-lightpath-group. The RWTA ILP is solved by the ILOG CPLEX optimization tool, and it is used to check the optimality of the RWTA heuristic. Performance tuning of the IMRWA heuristic is investigated to balance the tradeoff between performance and computation complexity. Performance tuning of the BVOG network with the RWTA and IMRWA heuristic is examined through simulation experiments.

CODE SIZE REDUCTION FOR ARRAY INTENSIVE APPLICATIONS ON DIGITAL SIGNAL PROCESSORS

Optimizing the code size for applications that run on a digital signal processors (DSPs) is a crucial step in generating high-quality and efficient code. Most modern DSP provide multiple address registers and dedicated address generation units that provide address generation in parallel to instruction execution. There is no address computation overhead if the next address is within the auto-modify range of the address register. Many DSP algorithms have an iterative pattern of references to array elements within loops. Thus, a careful assignment of array references to address registers (called the address register allocation or ARA problem) reduces the number of explicit address arithmetic instructions as well as the execution cycles. In this paper, we present an optimal integer linear programming formulation for the address register allocation problem which incorporates code restructuring techniques. In addition, we have developed a Genetic Algorithm solution for the ARA problem that allows us to get near-optimal solutions in a reasonable amount of time for large embedded applications. Results on several benchmarks show the effectiveness of our techniques compared to other techniques in the literature.

Formulation of Analytical Time-Varying Intermodal Person Trip Assignment Model

An analytical formulation of the intermodal dynamic traffic assignment problem is presented. The model is a cell transmission-based, single-destination, system optimal integer linear programming formulation for a multimodal network of cars and buses. The computational tests demonstrate interesting insights into the complex interactions between travelers' intermodal path choices and traffic movements. Specifically, as with many analytical time-varying traffic models, the constraints regulate flow, while the objective function provides an incentive for travelers to progress on least-cost paths toward the cost-free trip termination cells. It is found that difficulties relate to this reliance on costs to advance travelers and vehicles; for example, the non-first-in-first-out propagation of buses ahead of automobiles is a result of the higher cost incurred by numerous riders on a single bus vehicle. Similarly, the model's tendency to hold buses at bus stops or force buses to skip bus stops results from a difference in costs incurred by travelers who would be better served by the holding of the bus or by the skipping of a stop. On the basis of the findings on the model's behavior, recommendations are made for the future development of time-varying intermodal routing problems.