Gee-Swee Poo

A survey of optical multicast over WDM networks

Multicast applications such as multimedia, medical imaging, digital audio and video conferencing are bandwidth-intensive. With the advance in optical technology providing abundant bandwidth, it is natural to extend the multicast concept to optical networks in order to gain enhanced performance. This paper provides a comprehensive review of optical multicast techniques, covering the main optical multicast concept, the optical multicast switches, the multicast over single-hop broadcast-and-select networks, the multicast over multi-hop wide area mesh networks, and the related challenging algorithms developed for multicast routing in the optical domain.

Optical multicast over wavelength-routed WDM networks: A survey

With the rapid development of optical networking technology, it is now a realizable technique to support point-to-multipoint connections directly on the optical layer, giving rise to optical multicast. The topic of optical multicast has attracted much enthusiasm in recent years for the reason that it will not only make full use of the abundant bandwidth provided by optical fibers, but also take full advantage of multicast over the traditional point-to-point connection approach. In this paper, we present a comprehensive review of optical multicast over wavelength-routed WDM networks, covering the development of both data plane and control plane designs. In particular, we provide an up-to-date state-of-the-art review on the multicast routing and wavelength assignment problem. To the best of our knowledge, this is the most thorough and comprehensive review conducted so far on this topic in the literature.

User-oriented hierarchical bandwidth scheduling for ethernet passive optical networks

Ethernet passive optical networks (EPONs) are being designed to deliver different quality of service (QoS) to carry heterogeneous traffic of end users. For this purpose, hierarchical scheduling is needed for upstream bandwidth allocation, with high-level scheduling for inter-optical network unit (ONU) allocation and low-level scheduling for intra-ONU distribution. In this paper, we propose new User-oriented Hierarchical bandwidth Scheduling Algorithms (UHSAs) that support differentiated services and guaranteed fairness among end users. For inter-ONU scheduling, we adopt an improved hybrid cycle approach that separates a frame into a static part for high priority traffic and an adaptive dynamic part for low priority traffic. For intra-ONU scheduling, we propose credit-based scheduling approach to guarantee fairness among end users. To improve scheduling efficiency and lower queue management complexity, we design a novel credit-based common queue (CCQ) for each traffic class to enhance scheduling architecture and minimize average number of queues in the ONU. On the other hand, we propose a transmission priority scheme for different queue groups, which together with CCQ mechanism serves the objective of improving delay and delay variation performance of high priority traffic, guaranteeing throughput for bandwidth sensitive medium priority traffic, as well as providing fairness and throughput protection among different users. The UHSAs exhibit a feature of multiple transmission opportunities (M-opportunities) per-cycle for high priority traffic that is significant in improving delay and delay variation performance for high priority traffic as compared with previous solutions of single transmission opportunity (S-opportunity) per-cycle. Detailed simulation experiments are conducted to study the performance and validate the effectiveness of the proposed protocols.

Multi-path routing versus tree routing for VPN bandwidth provisioning in the hose model

In this paper we study the bandwidth provisioning of VPN service in the hose model with multi-path routing and tree routing. We have investigated the bandwidth efficiency and blocking performance of these two routing schemes. Our study shows that without any restriction on the maximum fraction of traffic on a path (MFTP), multi-path routing often turns out to be single path routing, and only reduces the total bandwidth requirement slightly at rare combination of network topologies and hose parameters. In order to alleviate the overprovisioning problem of the hose model, we propose the concept of sub-provisioning and study the blocking performance using static reduced provisioning. The results show that with full provisioning, the two routing schemes have almost the same blocking performance. However, with sub-provisioning and the variation of the MFTP constraint, multi-path routing is capable of delivering a significant improvement in blocking performance, often better than tree routing by a few orders of magnitude. The improvement is attributed to the multiple alternative paths brought in by the MFTP constraint. With sub-provisioning, the link bandwidth availability becomes the restricting factor in admitting a connection. Having multiple paths, a connection request is able to explore available bandwidth more thoroughly in the network, thus increasing its chances of being admitted. We employ both analytical model and discrete event simulation for the blocking performance study. The analytical model is developed based on the multi-rate reduced load approximation technique and the simulation is carried out using the OPNET simulator. The close agreement between analytical and simulation results indicate the validity of the approach.

A new multiwavelength multicast wavelength assignment (MMWA) algorithm in wavelength-routed WDM networks

This paper addresses the multicast wavelength assignment problem in wavelength-routed WDM networks with full light splitting and wavelength conversion capabilities. Current approach is based on the assumption that only one available wavelength can be used in a link. This assumption is rather restrictive. In this paper, we liberalize the assumption by allowing multiple available wavelengths in a link to carry the multicast signal. Consequently, based on a multicast-capable switch model, we develop a new multiwavelength multicast wavelength assignment (MMWA) algorithm to carry the multicast signal. Simulation results show that our new algorithm outperforms the existing MNWC algorithm by making significant reduction of wavelength conversion cost. The improvement percentage of MMWA is sensitive to the maximum out-degree value of a node, D. For L=10 (L being the maximum number of available wavelengths on each link), the improvement percentage increases from 20% at D=4 to about 70% at D=16. This is a significant improvement.

An expanded graph model for MCRWA problem in WDM networks

The future multimedia applications demand large bandwidth and require efficient multicast for economic use of network resources. The wavelength division multiplexing (WDM) networks have emerged as a promising technology to support high bandwidth demands. This paper proposes an expanded graph model to handle the multicast routing and wavelength assignment (MCRWA) problem in WDM optical networks. In the model, the WDM network is transformed into a graph. Application of graph theory algorithm will enable the routing and wavelength assignment to be done in a single step. The model is of general nature and is applicable to all kinds of WDM networks. We apply a degree-constrained SPH heuristic as an example to solve the MCRWA problem in a general WDM network that possesses finite light splitting and wavelength conversion capabilities. The simulation results show the broking performance of the optical networks under various constraints.

Dynamic multicast routing and wavelength assignment using generic graph model for wavelength-division-multiplexing networks

The problem of dynamic multicast routing and wavelength assignment (MC-RWA) in the wavelength-routed wavelength-division-multiplexing networks is addressed. Current solutions to this problem always rely on homogeneous network constructions. However, future backbone networks tend to be heterogeneous in nature. Thus, the dynamic MC-RWA problem should be studied in a more realistic situation by considering the heterogeneity of network structures. A new graph model is proposed for the MC-RWA problem. This model is based on layered auxiliary graph which is generic and able to support various node architectures and heterogeneous network structures. Based on this graph model, the dynamic MC-RWA problem can be simply solved by an efficient multicast tree algorithm on various light-splitting and wavelength-conversion scenarios. In general, this graph model provides a universal platform to study different aspects of the dynamic MC-RWA as well as related problems.

Layered-routing approach for solving multicast routing and wavelength assignment problem

We have developed a new layered-routing approach to address the problem of all-optical multicast over wavelength-routed wavelength division multiplexing (WDM) networks. We model the WDM network as a collection of wavelength layers with sparse light- splitting (LS) and wavelength conversion (WC) capabilities. We apply the degree constraint technique to solve the problem. The approach is capable of completing multicast routing and wavelength assignment (MCRWA) in one step. We propose two generic frameworks to facilitate heuristic development. Any heuristic that is derived from either Prim’s or Kruskal’s algorithm can be easily imported to solve the MCRWA problem. One example is given for each framework to demonstrate heuristic development. Extensive simulations were carried out to measure the performance of heuristics developed from the frameworks. The results show that the STRIGENT scheme is suitable for hardware design and it is advisable to deploy light splitters and wavelength converters to the same node for better performance.

Optimal placement of multicast and wavelength converting nodes in multicast optical virtual private network

This paper addresses multicast-nodes (MC-nodes) and wavelength converting-nodes (WC-nodes) placement problem in multicast optical virtual private network (M-OVPN). This problem is motivated by the high cost incurred in the usage of optical splitters and converters in the VPN due to complexity and power considerations. An analytical model for computing the approximate blocking probability in M-OVPN with wavelength conversion has been developed. The placement is determined using our proposed innovative removal algorithm together with the blocking performance computed. We perform simulation studies of our algorithms using NSFNET. The results show that the removal heuristic is able to locate the optimal placement location within a much shorter time and with higher efficiency compared to existing heuristic. In addition, we also show the flexibility of the heuristics by introducing the hybrid (combined removal) and dual (concurrent removal) removal mode

Placement of wavelength converters and light splitters in a WDM network using the generic graph model

Previous studies on the placement issue mainly focus on the availability of wavelength converters or light splitters on each node and normally the placement of wavelength converters and light splitters are considered in isolation. In this paper, by extending our previous work on the generic graph model, we study the placement of wavelength converters and light splitters as well as how their capabilities will affect the cost efficiency and performance in a holistic manner. In our study, both the sparse and limited capability strategies are considered, so is the coexistence of both wavelength converters and light splitters in the same network. The dynamic multicast traffic model is used for the simulation study. Four proposed algorithms, namely, WCF-I, WCF-D, LSF-I and LSF-D, for finding the optimal configuration of wavelength converters and light splitters are studied. The configuration includes information on the availability as well as the capability (and limitation) of the devices on each node in the network. Three metrics: cost efficiency (CE), request blocking probability (RBP) and average multicast tree cost (AMTC) are used to compare the different algorithms. All of the proposed algorithms manage to find a placement configuration with higher CE and comparable RBP, compared to the case of wavelength converters and light splitters having full capability of wavelength conversion and light splitting on all the nodes. From the results, we conclude that the presence of wavelength converters contributes more to improving the cost efficiency than the presence of light splitters when traffic load is not high. We also conclude that the sparse strategy has more impact on the performance than the limited strategy. In addition, our results led us to believe that the configuration that is obtained for a specific traffic load is not necessary the optimal configuration for other traffic loads.