Recent trends in science applications call for long-range and large-scale collaboration among laboratories and super-computing sites. Long gone are the days of entering data manually into a spreadsheet on a local workstation. The world's most powerful and ground-breaking experiments generate exabytes of information, which must be distributed to multiple labs for analysis and interpretation. Such trends reveal the unwavering importance of new communication paradigms, like multicasting and manycasting, which provide point-to-multipoint data transfers. Typically, these all-important mechanisms are provided at the optical layer, where split-capable cross-connects split input signals into multiple output signals all-optically. Unfortunately, some of the world's largest and most powerful networks do not have the hardware infrastructure to support such functionality, but allow for point-to-point communication exclusively. In such split-incapable (SI) networks, multicast and manycast must be provided as a logical overlay to the pre-existing and limited unicast infrastructure. In this paper, we present two overlay models for providing manycast support in SI networks: Manycasting with Drop at Member Node (MA-DMN) and Manycasting with Drop at Any Node (MA-DAN). Through the development of integer linear programs (ILPs) and heuristics, we evaluate these models in terms of both optimal solutions and efficient approximations for both small-scale and large-scale networks and consider both static and dynamic traffic scenarios. Our results demonstrate that despite a small tradeoff in additional complexity and delay from signal conversion to the optical domain, our models provide efficient utilization of network resources and greatly surpass the standard naive approach of establishing paths to every destination.

Recent explosion of high-bandwidth applications and scientific collaboration has expedited the need for scheduled transmission of data to multiple scientific sites around the world. Advance reservations (AR) promote efficient bandwidth utilization, particularly when demands are high. The collaborative nature of modern science calls for more flexible point-to-multipoint distribution paradigms, such as manycasting. Combining AR and manycast communication mechanisms enables intelligent resource utilization in optical networks to support future e-science applications. Limiting the adoption of point-to-multipoint communication is the physical handicap that many optical crossconnects are Split-Incapable (SI), i.e., all-optical splitting of signals is not supported, making optical AR manycasting infeasible. In this paper, we adapt solutions which have previously only been considered in immediate reservation (IR) scenarios to provide manycasting as a multi-hop logical overlay to the unicast-only optical layer. We develop ILPs and heuristics to evaluate the resource consumption for various AR traffic scenarios1.

In this paper we investigate techniques for provisioning advanced reservation multicast requests in Multicast-Incapable (MI) networks, which lack the ability to split an incoming signal to multiple output ports, without performing an O-E-O conversion. To implement the multicasting functionality in a MI network, we propose implementing it as a logical overlay to the optical layer. One such method is to reserve unicast lightpaths from the source node to each destination node of the multicast request. Referred to as Multicast Via WDM Unicast (MVWU), this solution tends to utilize the network resources in an inefficient manner. To address this problem we propose two novel overlay solutions: Drop At Member Node (DAMN) and Drop At Any Node (DAAN), wherein we create a set of lightpath routes (possibly multiple-hop) in the overlay layer to reach all the destinations of a multicast request. In DAMN, we allow a lightpath to terminate/originate only at nodes which belong to the set of destination nodes of the multicast request. DAAN relaxes this constraint and allows a lightpath to be terminated at any node in the network. We refer to the set of lightpath routes created in the overlay layer as overlay-trees. We consider dynamic traffic and present efficient heuristics to solve the MVWU, DAMN, and DAAN problems with a goal of minimizing the blocking probability of a request. Our results indicate that DAMN and DAAN outperform the MVWU approach. Further, we present different mechanisms to generate the overlay-trees and compare their relative performance on a real-world large-scale network.

Traditionally in wavelength division multiplexed (WDM) networks, multicasting is accomplished by splitting the signals all-optically, thereby establishing a tree of lightpaths (light-tree) from the source to every destination. To provision for this functionality in a Multicast-Incapable environment, in which the switches are not capable of directing an incoming signal to more than one output interface, one must implement a logical multicast overlay to the underlying optical layer. A naive method of accomplishing this is by creating a set of unicast lightpaths from the source to each destination of the multicast request. However, for large multicast groups, this leads to a poor utilization of the network resources. To alleviate this problem, we present two multicast Steiner tree overlay alternatives: Multicast with Drop At Member Node (DAMN), in which a lightpath may only terminate at member nodes of the multicast request, and Multicast with Drop At Any Node (DAAN), in which lightpaths may terminate at any node in the physical topology. We consider a dynamic traffic model, and propose efficient heuristics to solve the DAMN and DAAN problems with a goal of minimizing the total number of wavelengths required to satisfy the request. Moreover, we present a simple heuristic to approximate the baseline unicast approach (naive method). Our results demonstrate that at various loads, both the DAMN and DAAN reduce wavelength consumption by 42 - 60% over the naive unicast approach in realistic networks.

With the increasing number of high-bandwidth applications, energy consumption of networks has become an important issue that needs to be addressed. Manycasting is a communication paradigm that finds applications in such high-bandwidth environments. To support manycasting functionality in an optical network that is Split-Incapable (SI), i.e., the optical cross connects are incapable of switching an incoming optical signal to more than one output interface, manycasting must be implemented as an overlay to the optical layer. We propose two such overlay approaches: Manycasting with Drop at Member Node (MA-DAMN) and Manycasting with Drop at Any Node (MA-DAAN) which employ Steiner tree routing. We subject these approaches to a static traffic model, and present integer linear programs (ILPs) and heuristic approximations which aim to minimize the total number of wavelengths required to service the manycast request set in an effort to reduce network-wide energy consumption. Through extensive simulation, we show that MA-DAMN and MA-DAAN achieve 25-45% wavelength reduction as compared to a baseline overlay approach which employs single-hop lightpaths to each manycast destination individually.

In this paper we investigate the problem of provisioning dynamic anycast holding-time-aware (HTA) lightpaths in all-optical wavelength division multiplexed (WDM) networks. We employ a technique called lightpath switching (LPS) wherein the data transmission may begin on one lightpath and switch to a different lightpath at a later time. We propose two heuristics to solve the anycast routing and wavelength assignment (RWA) problem: anycast with continuous segment (ACS) and anycast with lightpath switching (ALPS). We first compare the performance of ACS to ALPS and observe that ALPS achieves better blocking than ACS. Furthermore, we also compare the performance of these two anycast RWA algorithms to the traditional unicast RWA algorithm. We show that the anycast RWA algorithms presented here significantly out-perform the traditional unicast RWA algorithms.

An all-optical approach to achieve finer bandwidth granularity is to time division multiplex low capacity circuits on each wavelength channel and to switch time-wavelength slots within the network. In such a Time-Wavelength-Switched- Network (TWSN), the Time-Wavelength-Space-Routers (TWSRs) are configured to change their routing pattern on a time slot basis. Another kind of time slotted network proposed in the literature is the Time-Wavelength-Interleaved Network (TWIN), which eliminates time switching within the network by using a non-reconfigurable core and an intelligent edge utilizing a fast tunable laser to emulate fast switching. A drawback of the TWIN network is that it assigns a unique wavelength to each node in the network. Thus it requires a total of W = N wavelengths for an N-node network and hence is not scalable. In this paper we propose to design a wavelength-constrained (i.e., W <; N) TWIN network with no switching (TWIN-NS) by using a multicasting strategy. We also propose a variant of the TWIN network which possesses switching capabilities only at the edge nodes (TWIN-ES), and compare the performances of these TWIN networks to that of the TWSN. We present integer linear programs and heuristic algorithms to solve the connection scheduling problem in the TWSN and the TWIN, and investigate the benefits of having a fast reconfigurable switch as opposed to a non-reconfigurable core.

Time-Wavelength-Switched Networks (TWSNs) provide a finer bandwidth granularity than traditional wavelength routing networks. In TWSNs, time on every wavelength is slotted and the crossconnects are configured to switch slots within a frame, and connections are assigned one or more slots per frame. Fiber Delay Line (FDL) banks within the crossconnects can reduce the probability of connection blocking due to output slot contention. In this paper, we consider the optimal construction of an FDL bank with a limited number of recirculations through the FDLs. Specifically, given a frame consisting of M slots, an FDL bank of D FDLs per output link, we develop a method to find a set of delay values D={d1, d2,...dD} such that the set of achievable delays using no more than K recirculations through the bank is maximized. Maximizing the number of achievable delays provides more flexibility in slot provisioning for connections, and is expected to decrease the blocking probability. We investigate the impact of the FDL configuration on a CrossConnect's performance. Our results show that the optimal FDL bank construction presented here achieves better blocking than previously considered FDL bank configurations. We also present a solution to the FDL bank design problem for an optical packet switch, and show through simulations that packet drop probability is considerably reduced for the optimal configuration.

An all-optical approach to reduce the speed mismatch between electronic sources and high-speed wavelength channels is to time-division multiplex low-capacity circuits onto each wavelength, and switch time-wavelength-slots within the network. In such a Time-Wavelength-Switched Network (TWSN), fiber delay lines (FDLs) and wavelength conversion (WC) can increase the flexibility in connection slot scheduling and decrease the connection blocking probability. In this paper, we examine the impact of various FDL configurations and WC on a CrossConnect's performance by looking at its ability to schedule as many connections as possible from a given traffic matrix. We present several crossconnect architectures and develop graph formulations that can be used to optimally solve the scheduling problem. Using numerical simulation results, we then compare several FDL configurations. Results show that FDL configurations and WC could play an important role in determining performance.