Multicast Capable Nodes Research Articles

Impairment-Aware Manycast Routing, Modulation Level, and Spectrum Assignment in Elastic Optical Networks

In this paper, we study the impairment-aware manycast routing, modulation level, and spectrum assignment problem in elastic optical networks. We formulate a mixed-integer linear program (MILP) that serves all the given manycast requests at once, referred to as a joint impairment-aware MILP. The formulated MILP can be used to jointly serve diverse traffic types, i.e., manycast, multicast, anycast, and unicast requests. In this formulation, nonlinear interference noise generated in fibers, the noise of optical amplifiers, the limitation of the maximum splitting degree of multicast-capable nodes (MCNs), and the power penalty of splitting the data flow into multiple branches at MCNs are considered. Furthermore, by modifying the joint MILP, two decomposed MILPs and corresponding heuristic algorithms are proposed to find a light-tree and assign modulation level and spectrum to the given requests, sequentially. We simulated the proposed heuristic algorithms and joint MILP (as a benchmark) and compared them with their distance-adaptive (DA) alternatives by considering a small-scale network. Our results reveal that our heuristic algorithms perform close to the joint MILP and have lower spectrum consumption than the DA alternatives. Furthermore, the performance of the heuristic algorithms is evaluated by considering a large-scale network. We observe that the number of occupied frequency slots and the average SNR of the network depend on the transmission power, and there is an optimum value for transmission power that maximizes the spectral efficiency. Moreover, the results show that the impairment-aware schemes outperform their DA alternatives in terms of spectrum consumption.

Resource Allocation and Multicast Routing in Elastic Optical Networks

In this paper, we formulate an integer linear programming (ILP) to perform multicast routing and spectrum assignment (MRSA) in elastic optical networks, which serves jointly a set of multicast requests. In this formulation, all physical layer restrictions including modulation level assignment, maximum number of multicast capable nodes (MCNs), and maximum splitting degree (MSD) of MCNs, are considered. In addition, we modify the proposed joint ILP to serve multicast requests one-by-one, which is referred to as a separate ILP. Furthermore, we present three heuristic algorithms for MRSA, namely distance-based MRSA (DMRSA), congestion-based MRSA (CMRSA), and mixed CMRSA/DMRSA, which are applicable in both static and dynamic operation scenarios. In CMRSA and DMRSA, the link length and the amount of occupied spectrum are considered as the cost function of multicast routing, respectively; and in mixed CMRSA/DMRSA, a combination of normalized link length and normalized occupied spectrum is considered as the cost function. The comparison of ILPs and heuristic algorithms in static operation reveals that the joint ILP, as the benchmark, gives the optimum solution while has the most computational complexity. Furthermore, the separate ILP has lower complexity at the cost of consuming slightly more spectrum. Unless the DMRSA method, which has the worst performance, the gap between the other two heuristic algorithms and the ILPs is negligible. Furthermore, simulation results of dynamic operation scenarios reveal that mixed CMRSA/DMRSA outperforms other two heuristics algorithms in terms of blocking probability.

Heuristic algorithms for efficient allocation of multicast-capable nodes in sparse-splitting optical networks

Optical splitters are utilized in optical nodes for splitting the received signal into multiple copies, in order to efficiently provide multicast capabilities in optical networks. In practice, only a fraction of the network nodes are equipped with optical splitters. These nodes are called multicast-capable (MC) and the remaining nodes are called Multicast Incapable (MI). In some networks, if the MI nodes are destinations of the multicast request, they can drop a small fraction of the incoming signal’s power locally and transmit the rest to the next node. This ability is called Drop-and-Continue (DaC) and the relevant networks are called DaC networks. In the absence of the DaC capabilities, the network is called Drop-or-Continue (DoC). The current paper deals with both aforementioned categories of networks, and proposes three heuristic algorithms for the efficient allocation of a limited number of MC nodes in the network, so as to achieve a low average cost of the light-trees that are calculated for routing the multicast requests. It is shown through simulations that the proposed techniques significantly outperform the relevant conventional splitter placement techniques. This work also investigates the impact of networks having DaC rather than DoC capabilities, as well as the impact of the percentage of MC nodes on the network performance, providing guidance for the efficient design of optical networks with sparse multicasting capabilities.

SPECTRAL THREAT IN TCP OVER OPTICAL BURST SWITCHED NETWORKS

Exponential increase in the number of online users has increased over the years posed a demand for high speed core architecture for the internet. The Optical Burst Switching (OBS) is a new switching architecture that efficiently utilizes the bandwidth of the optical layer. It offers all-optical switching as there is no Optical-Electronic conversion at any intermediate switching node. It is one of the three optical switching architectures, while others being Optical Circuit Switching (OCS) and Optical Packet Switching (OPS). The basic switching entity of OBS is a burst which posses an intermediate granularity between a packet and the amount of optical data in a circuit. The OBS architecture merits the shortcomings of the other two optical architectures namely OCS and OPS. This efficient core networking architecture, suffers from various security vulnerabilities. This paper proposes a novel security threat namely the spectral threat. It is a threat that affects only multicast capable nodes. Multicast Capable nodes are those nodes that are capable of multicasting an optical data. The wavelength of the optical data burst is altered resulting in flooding of data to a particular outgoing channel and ultimately blocking the channel. The attack results in losses thereby reducing the burst throughput and increasing the burst latency. The paper further summarizes other potential threats affecting normal nodes and Multicast Capable nodes for TCP over OBS networks.

Upgrading unicast nodes to multicast-capable nodes in all-optical networks

We consider the problem of upgrading unicast all-optical networks to support multicast communication. In upgrading, it is necessary to modify the existing nodes to support optical multicast switching. It is desirable to: (i) retain and use the existing node components while adding the necessary components so that the upgrading cost is small, and (ii) avoid major modification of the existing node architecture so that the upgrading overhead is small. We propose three designs to realize these two goals: (i) the pre-splitting design adds splitting modules before the existing optical switches where a splitting module can split incoming light beams into multiple ones, (ii) the post-splitting design adds splitting modules after the existing optical switches, and (iii) the pre/post-splitting design adds splitting modules before and after the existing optical switches. The pre-splitting design and post-splitting designs are simpler and involve lower upgrading overhead, while the pre/post-splitting design gives smaller blocking probability and achieves better cost-effectiveness by suitably selecting the number of splitting modules of each type.

Performance assessment of multicast node placement for multicast routing in WDM networks with sparse light splitting

This article examines all-optical multicast routing for wavelength-routed optical networks with sparse Multicast Capable (MC) nodes in two phases. The first phase is MC node placement and use of a simple and straightforward Maximum Path Count First (MPCF) algorithm to obtain candidates for MC nodes. The second phase is multicast routing with MC-based schemes that minimizes the number of wavelength channels with minimum transmission delay as required by a given multicast session, in that a light-tree is first constructed to connect MC nodes in a multicast group by using two algorithms, namely, the Pre-computing Minimum Cost (PMC) tree algorithm and the Pre-computing Shortest Path (PSP) tree algorithm. System performance of the proposed MPCF MC node placement algorithm is compared with that of the Normalized Cuts (NC) MC node placement algorithm for both PMC and PSP multicast routing. Furthermore, simulation results compare PMC and PSP multicast routing based on MPCF and NC node placement with Re-route-to-Source (RTS), Re-route-to-Any (RTA), Member-First (MF), and Member-Only (MO) multicast routing based on a light forest for a given multicast session in terms of average number of wavelengths needed, average blocking probability, and mean maximum transmission delay.

Performance analysis of optical multicast in a new switching structure

The emergence of new services demands multicast function in optical network. Because of the high cost and complex architecture of multicast capable (MC) node, splitter-sharing switch structure is introduced in which the light splitters are shared by all input signals. To accommodate to this situation, by extending resource ReSerVation protocol-traffic engineering (RSVP-TE) and open shortest path first-traffic engineering (OSPF-TE), a new optical multicast mechanism is provided and the signaling flow and its finite state machine model are given. At the same time, a multicast routing algorithm in splitter-sharing optical network and a changing link weight policy to balance network traffic are proposed. Simulations in NSFNET show no matter with or without wavelength converters, when the number of splitters is 25% of that demanded by traditional MC nodes, the multicast performance has been close to the ideal circumstance. Wavelength converters and changing link weight help much in improving the traffic performance when the number of splitters is adequate.

A novel efficient multicast routing algorithm in sparse splitting optical networks

The advances in wavelength-division multiplexing (WDM) technology are expected to facilitate bandwidth-intensive multicast applications through light splitting. Due to complexity and cost constraints, light splitting (or optical multicast) nodes are sparsely configured in a practical WDM network. In this article, we investigate the multicast routing problem under the sparse light-splitting constraint. An efficient sparse splitting constrained multicast routing algorithm called Multicast Capable Node First Heuristic (MCNFH) is proposed. The key idea of MCNFH is to include the shortest path, that includes most of the multicast capable nodes, for configuring the multicast tree. Simulations and comparisons are used to demonstrate the performance of MCNFH. Simulation results and analysis show that MCNFH builds multicast trees with the least wavelength channel cost and with the smallest number of wavelengths used per link. In addition, MCNFH requires only one transmitter at the source node.

Topology based placement of multicast capable nodes for supporting efficient multicast communication in WDM optical networks

Most existing algorithms for the problem of optical signal splitter placement or multicast splitting-capable node placement in a WDM network are based on the performance of attempting a large set of randomly generated multicast sessions in the network. Experiments show that placement of multicast capable nodes based on their importance for routing one set of multicast sessions may not be a right choice for another set of multicast sessions. In this work, we propose placement algorithms that are based on network topology and the relative importance of a node in routing multicast sessions, which is measured by our proposed metrics. Since a network topology is fixed once given, the proposed algorithms are essentially network traffic independent. We evaluate the proposed placement algorithms given static sets of multicast sessions as well as under dynamic traffic conditions, which are routed using our splitter constrained multicast routing algorithm. Our results show that the proposed algorithms perform better, compared to existing algorithms.

Routing in sparse splitting optical networks with multicast traffic

In this paper, we investigate the problem of Multicast Routing in Sparse Splitting Networks (MR-SSN). Given a network topology with the multicast capable nodes distributed uniformly throughout the network, and a multicast session, the MR-SSN problem is to find a route from the source node of the multicast session to all destinations of the multicast session such that the total number of fibers used in establishing the session is minimized. In this paper, we develop a rerouting algorithm for a given Steiner tree, which makes it feasible to route a multicast session using a tree-based solution in sparse light splitting optical networks. In addition, we present a heuristic based on Tabu Search (TS) that requires only one transmitter for the source node and one wavelength for each multicast session. To evaluate the performance of heuristics, we formulate the MR-SSP problem as an integer linear program (ILP), and optimally solve small instances using the commercially available linear solver, CPLEX. We test our heuristic on a wide range of network topologies. Our experimental results show that: (1) The difference between our solution and ILP optimal solution, in terms of the number of fibers used for establishing a multicast session, is within 10% in almost all the instances and within 5% in about half of the instances. (2) The average delay, taken over all destination nodes, falls within three times the optimal value. (3) A sparse light splitting all-optical network with 30% of multicast capable cross-connects has an acceptable low cost and relatively good performance. (4) The improvement achieved by TS heuristic increases considerably when the session size is large, the number of Splitter-and-Delivery cross-connects is small, and the network connectivity is dense.