Multicast capacity of optical ring network with hotspot traffic: The bi-directional WDM packet ring

Packet-switching WDM ring networks with a hotspot transporting unicast, multicast, and broadcast traffic are important components of high-speed metropolitan area networks. For an arbitrary multicast fanout traffic model with uniform, hotspot destination, and hotspot source packet traffic, we analyze the maximum achievable long-run average packet throughput, which we refer to as multicast capacity, of bi-directional shortest path routed WDM rings. We identify three segments that can experience the maximum utilization, and thus, limit the multicast capacity. We characterize the segment utilization probabilities through bounds and approximations, which we verify through simulations. We discover that shortest path routing can lead to utilization probabilities above one half for moderate to large portions of hotspot source multi- and broadcast traffic, and consequently multicast capacities of less than two simultaneous packet transmissions. We outline a one-copy routing strategy that guarantees a multicast capacity of at least two simultaneous packet transmissions for arbitrary hotspot source traffic.     

The FT/sup /spl Lambda//-FR/sup /spl Lambda// AWG network: a practical single-hop metro WDM network for efficient uni- and multicasting

Single-hop wavelength-division-multiplexed (WDM) networks with a central passive star coupler (PSC), as well as single-hop networks with a central arrayed-waveguide grating (AWG) and a single transceiver at each node, have been extensively studied as solutions for the quickly increasing amounts of unicast and multicast traffic in the metropolitan area. The main bottlenecks of these networks are the lack of spatial wavelength reuse in the studied PSC-based networks and the single transceiver in the studied AWG-based metro WDM networks. This paper describes the development and evaluation of the FT/sup /spl Lambda//-FR/sup /spl Lambda// AWG network, which is based on a central AWG and has arrays of fixed-tuned transmitters and receivers at each node. Transceiver arrays are a mature technology, making the proposed network practical. In addition, the transmitter arrays allow for high-speed signaling over the AWG while the receiver arrays relieve the receiver bottleneck arising from multicasting in conjunction with spatial wavelength reuse on the AWG. The results from probabilistic analysis and simulation reported here indicate that the FT/sup /spl Lambda//-FR/sup /spl Lambda// AWG network gives particularly good throughput-delay performance for a mix of unicast and multicast traffic.     

Light trees: optical multicasting for improved performance inwavelength routed networks

We introduce the concept of a light-tree in a wavelength-routed optical network. A light-tree is a point-to-multipoint generalization of a lightpath. A lightpath is a point-to-point all-optical wavelength channel connecting a transmitter at a source node to a receiver at a destination node. Lightpath communication can significantly reduce the number of hops (or lightpaths) a packet has to traverse; and this reduction can, in turn, significantly improve the network's throughput. We extend the lightpath concept by incorporating an optical multicasting capability at the routing nodes in order to increase the logical connectivity of the network and further decrease its hop distance. We refer to such a point-to-multipoint extension as a light-tree. Light-trees can not only provide improved performance for unicast traffic, but they naturally can better support multicast traffic and broadcast traffic. In this study, we shall concentrate on the application and advantages of light-trees to unicast and broadcast traffic. We formulate the light-tree-based virtual topology design problem as an optimization problem with one of two possible objective functions: for a given traffic matrix, (i) minimize the network-wide average packet hop distance, or (ii) minimize the total number of transceivers in the network. We demonstrate that an optimum light-tree-based virtual topology has clear advantages over an optimum lightpath-based virtual topology with respect to the above two objectives     

The arrayed-waveguide grating-based single-hop WDM network: an architecture for efficient multicasting

Research on multicasting in single-hop wavelength-division-multiplexing (WDM) networks has so far focused on networks based on the passive star coupler (PSC), a broadcast device. It has been shown that multicasting performance is improved by partitioning multicast transmissions into multiple multicast copies. However, the channel bottleneck of the PSC, which does not allow for spatial wavelength reuse, restricts the multicast performance. We investigate multicasting in a single-hop WDM network that is based on an arrayed-waveguide grating (AWG), a wavelength routing device that allows for spatial wavelength reuse. In our network, optical multicasting is enabled by wavelength-insensitive splitters that are attached to the AWG output ports. Multicasts are partitioned among the splitters and each multicast copy is routed to a different splitter by sending it on a different wavelength. We demonstrate that the spatial wavelength reuse in our network significantly improves the throughput-delay performance for multicast traffic. By means of analysis and simulations, we also demonstrate that, for a typical mix of unicast and multicast traffic, the throughput-delay performance is dramatically increased by transmitting multicast packets concurrently with control information in the reservation medium access control protocol of our AWG-based network.     

Impact of cell fanout distributions on multicast ATM switchperformance

For shared buffer multicast ATM switches, it is found that the highest cell loss ratio may be caused by the unicast plus broadcast traffic given the mean cell fanout, or roughly by the maximum coefficient of variation of cell fanout given the fanout distribution     

Metro WDM networks: performance comparison of slotted ring and AWG star networks

Both wavelength-division-multiplexing (WDM) networks with a ring architecture and WDM networks with a star architecture have been extensively studied as solutions to the ever increasing amount of traffic in the metropolitan area. Studies typically focus on either the ring or the star and significant advances have been made in the protocol design and performance optimization for the WDM ring and the WDM star, respectively. However, very little is known about the relative performance comparisons of ring and star networks. In this paper, we conduct a comprehensive comparison of a state-of-the-art WDM ring network with a state-of-the-art WDM star network. In particular, we compare time-slotted WDM ring networks (both single-fiber and dual-fiber) with tunable-transmitter and fixed-receiver (TT-FR) nodes and an arrayed-waveguide grating-based single-hop star network with tunable-transmitter and tunable-receiver (TT-TR) nodes. We evaluate mean aggregate throughput, relative packet loss, and mean delay by means of simulation for Bernoulli and self-similar traffic models for unicast traffic with uniform and hot-spot traffic matrices, as well as for multicast traffic. Our results quantify the fundamental performance characteristics of ring networks versus star networks and vice versa, as well as their respective performance limiting bottlenecks and, thus, provide guidance for directing future research efforts.     

A cost effective approach for survivable multicast traffic grooming in bidirectional multiwavelength ring networks

In this paper, we address the problem of survivable multicast traffic grooming in WDM bidirectional ring networks. The rapid growth of multicast applications such as video conferencing, distance learning, and online auction, has initiated the need for cost-effective solutions to realize multicasting in WDM optical networks. Many of these applications, being time critical and delay sensitive, demand robust and fault-tolerant means of data communication. The end user traffic demands in metro environment are in fractional bandwidth as compared to the wavelength channel capacity. Providing survivability at connection level is resource intensive. Hence cost-effective solutions that require minimum resources for realizing survivable multicasting are in great demand. In order to realize multicast traffic grooming in bidirectional ring networks, we propose a node architecture based on Bidirectional Add Drop Multiplexers (BADM) to support bidirectional add/drop functionality along with traffic duplication at each node. We also propose two traffic grooming algorithms, namely Survivable Grooming with Maximum Overlap of Sessions (SGMOS) and Survivable Grooming with Rerouting of Sessions (SGRS). Extensive simulation studies reveal that the proposed algorithms consume minimum resources measured in terms of BADM grooming ports, backup cost, and wavelengths.     

Minimizing the Number of Multicast Transmissions in Single-Hop WDM Networks

The problem of minimizing the number of transmissions for a multicast transmission under the condition that the packet delay is minimum in single-hop wavelength division multiplexing (WDM) networks is studied in this paper. This problem is proved to be NP-complete. A heuristic multicast scheduling algorithm is proposed for this problem. Extensive simulations are performed to compare the performance of the proposed heuristic algorithm with two other multicast scheduling algorithms, namely, the greedy and no-partition scheduling algorithms. The greedy algorithm schedules as many destination nodes as possible in the earliest data slot. The no-partition algorithm schedules the destination nodes of a multicast packet to receive the packet in the same data slot without partitioning the multicast transmission into multiple unicast or multicast transmissions. Our simulation results show that (i) an algorithm which partitions a multicast transmission into multiple unicast or multicast transmissions may not always produce lower mean packet delay than the no-partition algorithm when the number of data channels in the system is limited and (ii) the proposed heuristic algorithm always produces lower mean packet delay than the greedy and the no-partition algorithms because this algorithm not only partitions a multicast transmission into multiple unicast or multicast transmissions to keep the packet delay low but also reduces the number of transmissions to conserve resources.     

Dynamic wavelength assignment for multicast in all-optical WDM networks to maximize the network capacity

We study the problem of wavelength assignment for multicast in order to maximize the network capacity in all-optical wavelength-division multiplexing networks. The motivation behind this work is to minimize the call blocking probability by maximizing the remaining network capacity after each wavelength assignment. While all previous studies on the same objective concentrate only on the unicast case, we study the problem for the multicast case. For a general multicast tree, we prove that the multicast wavelength assignment problem of maximizing the network capacity is NP-hard and propose two efficient greedy algorithms. We also study the same problem for a special network topology, a bidirectional ring network, which is practically the most important topology for optical networks. For bidirectional ring networks, a special multicast tree with at most two leaf nodes is constructed. Polynomial time algorithms for multicast wavelength assignment to maximize the network capacity exist under such a special multicast tree with regard to different splitting capabilities. Our work is the first effort to study the multicast wavelength assignment problem under the objective of maximizing network capacity.     

Scheduling Combined Unicast and Multicast Traffic in Broadcast WDM Networks

This paper studies the performance of various strategies for scheduling a combined load of unicast and multicast traffic in a broadcast WDM network. The performance measure of interest is schedule length, which directly affects both aggregate network throughput and average packet delay. Three different scheduling strategies are presented, namely: separate scheduling of unicast and multicast traffic, treating multicast traffic as a number of unicast messages, and treating unicast traffic as multicasts of size one. A lower bound on the schedule length for each strategy is first obtained. Subsequently, the strategies are compared against each other using extensive simulation experiments in order to establish the regions of operation, in terms of a number of relevant system parameters, for which each strategy performs best. Our main conclusions are as follows. Multicast traffic can be treated as unicast traffic, by replicating all multicast packets, under very limited circumstances. On the other hand, treating unicast traffic as a special case of multicast traffic with a group of size 1, produces short schedules in most cases. Alternatively, scheduling and transmitting each traffic component separately is also a good choice.     

RINGOSTAR: an evolutionary AWG-based WDM upgrade of optical ring networks

The paper describes the study of the multichannel upgrade of IEEE Standard 802.17 Resilient Packet Ring (RPR) in particular and optical single-channel ring networks in general by making use of wavelength-division multiplexing (WDM). The paper describes and discusses a novel evolutionary multichannel upgrade approach that uses WDM on a central passive arrayed-waveguide grating (AWG)-based single-hop star network rather than on the ring. The AWG-based star subnetwork allows for a dramatically larger spatial reuse of WDM wavelength channels than conventional upgrades of optical single-channel ring networks that use WDM on the ring where all nodes need to be WDM upgraded. In the resultant hybrid optical ring-star network, termed RINGOSTAR, only a subset of the nodes are required to be WDM upgraded with a single additional tunable transceiver in order to improve the performance dramatically. The novel concept of proxy stripping is also introduced, which is used to route ring traffic on single-hop short cuts across the star subnetwork rather than the peripheral ring, resulting in a dramatically increased spatial reuse factor on the ring. By means of analysis, the performance of RINGOSTAR is investigated in terms of mean hop distance, spatial reuse, and capacity. The findings show that RINGOSTAR significantly outperforms unidirectional, bidirectional, and meshed WDM rings. Finally, the tradeoffs of RINGOSTAR are addressed.     

Comprehensive performance modeling and analysis of multicasting in optical networks

Multicasting is becoming increasingly important in today's networks. In optical networks, optical splitters facilitate the multicasting of optical signals. By eliminating the transmission of redundant traffic over certain links, multicasting can improve network performance. However, in a wavelength-division multiplexed (WDM) optical network, the lack of wavelength conversion necessitates the establishment of a single multicast circuit (light-tree) on a single wavelength. On the other hand, establishing several unicast connections (lightpaths) to satisfy a multicast request, while requiring more capacity, is less constrained in terms of wavelength assignment. The objective of the paper is to evaluate the tradeoff between capacity and wavelength continuity in the context of optical multicasting. To this end, we develop accurate analytical models with moderate complexity for computing the blocking probability of multicast requests realized using light-trees, lightpaths, and combinations of light-trees and lightpaths. Numerical results indicate that a suitable combination of light-trees and lightpaths performs best when no wavelength conversion is present.     

Performance analysis of multicast routing and wavelength assignment protocol with dynamic traffic grooming in WDM networks

The need for on‐demand provisioning of wavelength‐routed channels with service‐differentiated offerings within the transport layer has become more essential because of the recent emergence of high bit rate Internet protocol (IP) network applications. Diverse optical transport network architectures have been proposed to achieve the above requirements. This approach is determined by fundamental advances in wavelength division multiplexing (WDM) technologies. Because of the availability of ultra long‐reach transport and all‐optical switching, the deployment of all‐optical networks has been made possible. The concurrent transmission of multiple streams of data with the assistance of special properties of fiber optics is called WDM. The WDM network provides the capability of transferring huge amounts of data at high speeds by the users over large distances. There are several network applications that require the support of QoS multicast, such as multimedia conferencing systems, video‐on‐demand systems, real‐time control systems, etc. In a WDM network, the route decision and wavelength assignment of lightpath connections are based mainly on the routing and wavelength assignment (RWA). The multicast RWA's task is to maximize the number of multicast groups admitted or minimize the call‐blocking probability. The dynamic traffic‐grooming problem in wavelength‐routed networks is generally a two‐layered routing problem in which traffic connections are routed over lightpaths in the virtual topology layer and lightpaths are routed over physical links in the physical topology layer. In this paper, a multicast RWA protocol for capacity improvement in WDM networks is designed. In the wavelength assignment technique, paths from the source node to each of the destination nodes and the potential paths are divided into fragments by the junction nodes and these junction nodes have the wavelength conversion capability. By using the concept of fragmentation and grouping, the proposed scheme can be generally applied for the wavelength assignment of multicast in WDM networks. An optimized dynamic traffic grooming algorithm is also developed to address the traffic grooming problem in mesh networks in the multicast scenario for maximizing the resource utilization and minimizing the blocking probability. Copyright © 2011 John Wiley & Sons, Ltd.     

Optimized multipath network coding in lossy wireless networks

Network coding has been a prominent approach to a series of problems that used to be considered intractable with traditional transmission paradigms. Recent work on network coding includes a substantial number of optimization based protocols, but mostly for wireline multicast networks. In this paper, we consider maximizing the benefits of network coding for unicast sessions in lossy wireless environments. We propose Optimized Multipath Network Coding (OMNC), a rate control protocol that dramatically improves the throughput of lossy wireless networks. OMNC employs multiple paths to push coded packets to the destination, and uses the broadcast MAC to deliver packets between neighboring nodes. The coding and broadcast rate is allocated to transmitters by a distributed optimization algorithm that maximizes the advantage of network coding while avoiding congestion. With extensive experiments on an emulation testbed, we find that OMNC achieves more than two-fold throughput increase on average compared to traditional best path routing, and significant improvement over existing multipath routing protocols with network coding. The performance improvement is notable not only for one unicast session, but also when multiple concurrent unicast sessions coexist in the network.     

All-Optical Wavelength-Bypassing Ring Communications Networks

We introduce an all-optical WDM packet communication network that performs wavelength bypassing at the routers. Packets that arrive at a wavelength (optical cross-connect) router at designated wavelengths are switched by the router without having their headers examined. Thus, the processing element of the router is bypassed by such packets. For packet traffic that uses wavelengths that do not bypass a switch, the headers of such packets are examined to determine if this switch is the destination for the flow. If latter is the case, the packet is removed. Otherwise, the packet is switched to a pre-determined output without incurring (network internal) queueing delays. We study a ring network with routers that employ such a WDM bypassing scheme. We present methods to construct wavelength graphs that define the bypassing pattern employed by the routers to guide the traffic flows distributed at each given wavelength. Performance is measured in terms of the network throughput and the average processing path length (i.e., the average number of switches not being bypassed). For a fixed total processing capacity, we show that a WDM bypassing ring network provides a higher throughput level than that exhibited by a non-bypassing ring network, using the same value of total link capacity. By using WDM bypassing, the average processing path length (and thus the packet latency) is reduced. We study a multitude of network loading configurations, corresponding to distinct traffic matrices and client-server scenarios. Higher throughput levels are obtained for network configurations driven by non-uniform traffic matrices. The demonstrated advantages of WDM bypassing methods shown here for WDM ring networks are also applicable to more general network topological layouts.     

Quantifying the benefit of configurability in circuit-switched WDMring networks with limited ports per node

In a reconfigurable network, lightpath connections can be dynamically changed to reflect changes in traffic conditions. This paper characterizes the gain in traffic capacity that a reconfigurable wavelength division multiplexed (WDM) network offers over a fixed topology network where lightpath connections are fixed and cannot be changed. We define the gain as the ratio of the maximum offered loads that the two systems can support for a given blocking probability. We develop a system model to approximate the blocking probability for both the fixed and reconfigurable systems. This model is different from previous models developed to analyze the blocking probability in WDM networks in that it accounts for a port limitation at the nodes. We validate our model via simulation and find that it agrees strongly with simulation results. We study high-bandwidth calls, where each call requires an entire wavelength and find that reconfigurability offers a substantial performance improvement, particularly when the number of available wavelengths significantly exceeds the number of ports per node. In this case, in a ring with N nodes, the gain approaches a factor of N/2 over a fixed topology unidirectional ring, and N/4 over a fixed topology bidirectional ring. Hence, a reconfigurable unidirectional (bidirectional) ring can support N/2(N/4) times the load of a fixed topology unidirectional (bidirectional) ring. We also show that for a given traffic load, a configurable system requires far fewer ports per node than a fixed topology system. These port savings can potentially result in a significant reduction in overall system costs     

An efficient dynamic multicast traffic-grooming algorithm for WDM networks

With the growth of multi-granularity multicast applications, there comes into being a huge gap between the bandwidth of a wavelength provided and a multicast traffic required in the wavelength division multiplexing (WDM) networks. The dynamic multicast traffic-grooming is an effective way for WDM networks to improve the wavelength utilization and decrease the traffic blocking probability. A novel switching node architecture with the multicast switching matrix and traffic-grooming fabric is studied in the paper. Then, an efficient dynamic multicast traffic-grooming algorithm is proposed for the architecture. According to the ratio of network available grooming port number to network transceiver number, the proposed algorithm estimates whether the traffic-grooming port is a scarce resource for input traffic and chooses the appropriate grooming strategy. If the traffic-grooming port is scarce, the minimized use grooming port strategy is designed for the coming traffic. On the contrary, the minimized use node transceiver strategy is applied for the coming traffic. Simulation results show that the proposed algorithm can groom traffic efficiently with low blocking probability and high network throughput constraint by limiting number of node transceivers and grooming ports.     

Optimal all-to-all broadcast in WDM optical networks with breakdown or power-off transceivers

All-to-all broadcast is an interesting special case of the packet transmission scheduling in which every pair of nodes has exactly one packet to be transferred. This paper considers the all-to-all broadcast problem in wavelength division multiplexed (WDM) optical star network with some breakdown or power-off transceivers. For reaching high data transmission rates, we will focus the problem on the all-optical scheduling where the traffic reaches its destination in single-hop without being converted to electronic form. Each transmitter is tunable with an associated tuning delay and each receiver is fixed-tuned to one of available wavelengths. In this model, we study two kinds of all-to-all broadcast problems depending on whether each node transmits packets to all nodes including or except itself. We identify the lower bound of the scheduling length for each kind of problems and propose single-hop scheduling algorithms to find the optimal solution in both terms of arbitrary number of wavelengths and value of tuning latency.     

Wireless network coding in slotted aloha with two-hop unbalanced traffic

This paper deals with two representative unbalanced traffic cases for two-hop wireless relay access systems employing network coding and a slotted ALOHA protocol. Network coding is a recent and highly regarded technology for capacity enhancement with multiple unicast and multisource multicast networks. We have analyzed the performance of network coding on a two-hop wireless relay access system employing the slotted ALOHA under a balanced bidirectional traffic. The relay nodes will generally undergo this unbalanced multidirectional traffic but the impact of this unbalanced traffic on network coding has not been analyzed. This paper provides closed-form expressions for the throughput and packet delay for two-hop unbalanced bidirectional traffic cases both with and without network coding even if the buffers on nodes are unsaturated. The analytical results are mainly derived by solving queueing systems for the buffer behavior at the relay node. The results show that the transmission probability of the relay node is a design parameter that is crucial to maximizing the achievable throughput of wireless network coding in slotted ALOHA on two-hop unbalanced traffic cases. Furthermore, we show that the throughput is enhanced even if the traffic at the relay node is unbalanced.     

ICAM: integrated cellular and ad hoc multicast

In third generation (3G) wireless data networks, multicast throughput decreases with the increase in multicast group size, since a conservative strategy for the base station is to use the lowest data rate of all the receivers so that the receiver with the worst downlink channel condition can decode the transmission correctly. This paper proposes ICAM, integrated cellular and ad hoc multicast, to increase 3G multicast throughput through opportunistic use of ad hoc relays. In ICAM, a 3G base station delivers packets to proxy mobile devices with better 3G channel quality. The proxy then forwards the packets to the receivers through an IEEE 802.11-based ad hoc network. In this paper, we first propose a localized greedy algorithm that discovers for each multicast receiver the proxy with the highest 3G downlink channel rate. We discover that due to capacity limitations and interference of the ad hoc relay network, maximizing the 3G downlink data rate of each multicast receiver's proxy does not lead to maximum throughput for the multicast group. We then show that the optimal ICAM problem is NP-hard, and derive a polynomial-time 4-approximation algorithm for the construction of the multicast forest. This bound holds when the underlying wireless MAC supports broadcast or unicast, single rate or multiple rates (4(1 + /spl isin/) approximation scheme for the latter), and even when there are multiple simultaneous multicast sessions. Through both analysis and simulations, we show that our algorithms achieve throughput gains up to 840 percent for 3G downlink multicast with modest overhead on the 3G uplink.