Ankitkumar N. Patel

Routing, wavelength assignment, and spectrum allocation algorithms in transparent flexible optical WDM networks

Abstract Current fixed grid wavelength routed networks are limited in terms of spectral efficiency due to the rigid nature of wavelength assignment. We propose the Flexible Optical WDM (FWDM) network architecture for flexible grid optical networks in which the constraint on fixed spectrum allocation to channels is removed and network resources can be dynamically provisioned with an automated control plane. In this paper, we address the routing, wavelength assignment, and spectrum allocation problem (RWSA) in transparent FWDM networks with the objective of maximizing spectral efficiency. We formulate the RWSA problem using an Integer Linear Program (ILP). We also prove the NP-completeness of the RWSA problem, and propose three efficient polynomial time algorithms; namely the Greedy-Routing, Wavelength Assignment, and Spectrum Allocation algorithm (Greedy-RWSA); the K -Alternate Paths Routing, Wavelength Assignment, and Spectrum Allocation algorithm (KPaths-RWSA); the Shortest Path Routing, Wavelength Assignment, and Spectrum Allocation algorithm (SP-RWSA). We analyze the lower bound on the required spectrum for the given network topology and a set of requests. Simulation results demonstrate that FWDM networks are efficient in terms of spectrum, cost, and energy compared to fixed grid networks. The performance of the proposed algorithms is very close to the lower bound, and approaches to the lower bound as problem size increases.

Traffic Grooming in Green Optical Networks

Compared to energy-awareness research in wireless and copper networks, less attention has been given to energy awareness in optical counterparts. In this paper, we introduce energy-aware traffic grooming problems for optical networks. We show that by looking further into the modular physical architecture of a node during request allocations, we can significantly reduce the number of active components and, hence, total energy consumption in the network, especially when traffic load is low. Since energy usage is an important element of operational expenditure (OPEX), this approach provides the financial motivation for service providers along with the desired environmental motivation. We present auxiliary graph based heuristics and justify our cases compared to traditional approaches with simulation results.

Routing, Wavelength Assignment, and Spectrum Allocation in Transparent Flexible Optical WDM (FWDM) Networks

We propose the flexible optical WDM network architecture, and introduce the routing, wavelength assignment, and spectrum allocation problem in transparent FWDM networks. Spectrum and cost efficiency are improved compared to fixed grid networks.

Traffic grooming and regenerator placement in impairment-aware optical WDM networks

In this paper, we address the problem of traffic grooming and regenerator placement in a WDM optical network in which lightpaths are hop-constrained by physical impairments. The efficient placement of regenerators and electronic grooming equipment at ROADM nodes for a given network topology is required such that all traffic demands can be supported with minimum cost. We present a detailed ROADM node architecture together with an associated cost model, and we propose an auxiliary-graph-based heuristic for jointly placing regenerators and electronic grooming equipment in the network. The numerical results show that combining the grooming problem with the placement of regenerators reduces the network cost significantly compared to the cases in which traffic grooming and regenerator placement are handled separately.

Survivable virtual infrastructure mapping with dedicated protection in transport software-defined networks [Invited]

Efficiently mapping multiple virtual infrastructures (VIs) onto the same physical substrate with survivability is one of the fundamental challenges related to network virtualization in transport software-defined networks (T-SDNs). In this paper, we study the survivable VI mapping problem in T-SDNs with the objective of minimizing the VI request blocking probability. In particular, we address the subproblems of modulation selection and spectrum allocation in the process of provisioning optical channels to support virtual links, taking into consideration the optical layer constraints such as the transmission reach constraint and the spectral continuity constraint. We propose an auxiliary-graph-based algorithm, namely, parallel VI mapping (PAR), to offer dedicated protection against any single physical node or link failure. More specifically, the PAR algorithm can jointly optimize the assignments of mapping the primary and backup VIs by adopting the modified Suurballe algorithm to find the shortest pair of node-disjoint paths for each virtual link. Through extensive simulations, we demonstrate that the PAR algorithm can significantly reduce the VI request blocking probability and improve the traffic-carrying capacity of the networks, compared to the baseline sequential VI mapping approaches.

Relay Node Placement in Vehicular Delay-Tolerant Networks

Delay-tolerant networking (DTN) is an architecture to enable data communications between isolated or remote regions, where long delays and intermittent connectivity can be tolerated. An emerging class of DTN, called vehicular DTNs (VDTN), exploits transportation systems as the transport layer to transfer data. In these networks, vehicles (e.g., busses, boats, trains) act as mobile nodes and carry data messages around. Mobile nodes can exchange data messages using devices called relay nodes. Relay nodes, placed in strategic positions along vehicle routes, have the capability to download, store, and upload the data messages from/to the mobile nodes. An important issue in VDTN is the optimal placement of the relay nodes such that delay-tolerant connectivity in VDTN is ensured at minimum cost. In this paper we show that the problem of optimal relay node placement is an NP-hard problem. Other contributions of this paper are the formulation of the relay node placement problem using ILP and the proposal of heuristic algorithms solving the optimization problem. Using simulation results, we compare the performance of each algorithm under different network constraints, such as node storage capability and network topology.

Routing and Scheduling for Variable Bandwidth Advance Reservation

Emerging elastic applications generate voluminous datasets, which are often required to be transferred across the network irrespective of flow level bandwidth guarantees. The primary concern in efficient transfers of such bulk data is to minimize the net transfer time. Variable bandwidth advance reservation (VBAR) can efficiently support such applications by reserving time variant bandwidth over the duration of a connection in advance. In this work, we address the routing and bandwidth scheduling problem in VBAR with the objective of minimizing the data transfer time. We propose three heuristic algorithms, and evaluate their performance for a single request under a given network state. We also evaluate the performance of the heuristics in a network under a dynamic traffic scenario. We demonstrate that VBAR outperforms conventional standard advance reservation and immediate reservation approaches in terms of delay, blocking probability, and network throughput. Furthermore, the performance of the proposed heuristic outperforms existing solutions in the dynamic traffic scenario with significantly lower time and storage complexities.

Vehicular Wireless Burst Switching Network: Enhancing Rural Connectivity

This paper introduces a network architecture called vehicular wireless burst switching (VWBS). The main objective of this architecture is to provide low-cost connectivity solution for isolated and dispersed regions with no networks infrastructure. The proposed architecture is based on the concept of delay tolerant networks (DTN) and can be applied to various scenarios, including rapid deployment of emergency communication systems when all communication links have failed. In this paper, we present an overview of VWBS networks and show how their performance, in terms of average packet delays, can be improved using store-and-forward devices called relay nodes. Furthermore, we introduce several heuristic algorithms, which can be used to place minimum number of relay nodes. Through computer simulations, we compare the performance of the algorithms and their tradeoffs. We conclude our work by examining possible open research issues in VWBS.

Wavelength contention-free via optical bypass within a colorless and directionless ROADM [invited]

A conventional colorless and directionless reconfigurable optical add/drop multiplexer (ROADM) architecture is modified to add intra-node optical bypass and achieve either statistical or absolute contention-free performance. The contention-free performance is accomplished without relying on external transponders and optical transport network (OTN) switches. Furthermore, the overall ROADM has a smaller size, lower power consumption, and lower cost than those of conventional colorless, directionless, and contentionless ROADMs.

Survivable impairment-aware traffic grooming and regenerator placement with connection-level protection

In this paper, we address the problem of survivable traffic grooming and regenerator placement in optical wavelength division multiplexing (WDM) networks with impairment constraints. The working connections are protected end to end by provisioning bandwidth along a sequence of lightpaths through either a dedicated or a shared connection-level protection scheme. We propose an auxiliary-graph-based approach to address the placement of regenerators and grooming equipment for both working and backup connections in the network in order to minimize the total equipment cost. Simulation results show that the proposed algorithms outperform lightpath-level protection algorithms, in which each lightpath is protected separately. We also show the performance of connection-level protection under both dedicated and shared protection schemes in terms of the network cost, along with the effect of different cost models on equipment placement and performance for networks with different line rates. The restoration time of dedicated and shared connection-level protection is also investigated.