a b s t r a c t 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.
In high-speed SONET rings with point-to-point WDM links, the cost of SONET add-drop multiplexers (S-ADMs) can be dominantly high. However, by grooming traffic (i.e., multiplexing lower-rate streams) appropriately and using wavelength ADMs (WADMs), the number of S-ADMs can be dramatically reduced. In this paper, we propose optimal or near-optimal algorithms for traffic grooming and wavelength assignment to reduce both the number of wavelengths and the number of S-ADMs. The algorithms proposed are generic in that they can be applied to both unidirectional and bidirectional rings having an arbitrary number of nodes under both uniform and nonuniform (i.e., arbitrary) traffic with an arbitrary grooming factor. Some lower bounds on the number of wavelengths and S-ADMs required for a given traffic pattern are derived, and used to determine the optimality of the proposed algorithms. Our study shows that using the proposed algorithms, these lower bounds can he closely approached in most cases or even achieved in some cases. In addition, even when using a minimum number of wavelengths, the savings in S-ADMs due to traffic grooming (and the use of WADMs) are significant, especially for large networks. A new and tight lower bound on the number of ADMs with arbitrary nonuniform traffic demands in a SONET WDM ring network is derived. Simulations show that this lower bound is much tighter than the previous one and for some cases it reaches the infimum. We study the SMARTNet (scalable multichannel adaptable ring terabit network), an optical wavelength-division packet-switching meshed-ring network employing wavelength routers. We investigate the ways to configure these wavelength routers in adapting to the underlying traffic matrix. One heuristic algorithm for this purpose is developed. We show that for any traffic matrix, the throughput performance of the SMARTNet employing wavelength cross-connect routing devices is upper bounded by that of a corresponding meshed-ring network employing store-and-forward switching devices. The difference diminishes as the number of employed wavelengths increases. Furthermore, for a specific meshed-ring: topology, we show that the above upper bound throughput level is achievable under uniform traffic loading at even a small number of wavelengths. Under nonuniform traffic loading, we show that a throughput level equal to 80 to 90 of the upper bound value can be achieved with a small number (five to seven) of wavelengths. This paper investigates the challenges for developing the current local area network (LAN)-based Ethernet protocol into a technology for future network architectures that is capable of satisfying dynamic traffic demands with hard service guarantees using high-bit-rate channels (80...100 Gb s). The objective is to combine high-speed optical transmission and physical interfaces (PHY) with a medium access control (MAC) protocol, designed to meet the service guarantees in future metropolitan-area networks (MANs). Ethernet is an ideal candidate for the extension into the MAN as it allows seamless compatibility with the majority of existing LANs. The proposed extension of the MAC protocol focuses on backward compatibility as well as on the exploitation of the wavelength domain for routing of variable traffic demands. The high bit rates envisaged will easily exhaust the capacity of a single optical fiber in the C band and will require network algorithms optimizing the reuse of wavelength resources. To investigate this, four different static and dynamic optical architectures were studied that potentially offer advantages over current link-based designs. Both analytical and numerical modeling techniques were applied to quantify and compare the network performance for all architectures in terms of achievable throughput, delay, and the number of required wavelengths and to investigate the impact of nonuniform traffic demands. The results show that significant resource savings can be achieved by using end-to-end dynamic lightpath allocation, but at the expense of high delay. In this paper, we study the benefits of using tunable transceivers for reducing the required number of electronic ports in wavelength-division-multiplexing time-division multiplexing optical networks. We show that such transceivers can be used to efficiently "groom" subwavelength traffic in the optical domain and so can significantly reduce the amount of terminal equipment needed compared with the fixed-tuned case. Formulations for this "tunable grooming" problem are provided, where the objective is to schedule transceivers so as to minimize the required number of ports needed for a given traffic demand. We establish a relationship between this problem and edge colorings of graphs which are determined by the offered traffic. Using this relationship, we show that, in general, this problem is NP-complete, but we are able to efficiently solve it for many cases of interest. When the number of wavelengths in the network is not limited, each node is shown to only require the minimum number of transceivers (i.e., no more transceivers than the amount of traffic that it generates). This holds regardless of the network topology or traffic pattern. When the number of wavelengths is limited, an analogous result is shown for both uniform and hub traffic in a ring. We then develop a heuristic algorithm for general traffic that uses nearly the minimum number of transceivers. In most cases, tunable transceivers are shown to reduce the number of ports per node by as much as 60 . We also consider the case where traffic can dynamically change among an allowable set of traffic demands. Tunability is again shown to significantly reduce the port requirement for a nonblocking ring, both with and without rearrangements.  Hotspot traffic is common in metro ring networks connecting access networks with backbone networks, and these metro rings are also expected to support a mix of unicast, multicast, and broadcast traffic. Shortest path (SP) routing, as employed in the IEEE 802.17 Resilient Packet Ring (RPR), is widely considered for metro rings as it maximizes spatial reuse and, thus, the achievable packet throughput (capacity) for uniform traffic. In this paper, we analyze the capacity of bidirectional optical ring networks, such as RPR, employing SP routing for multicast (nonuniform) hotspot traffic (whereby unicast and broadcast are considered as special cases of multicast). We find that, when the traffic originating at the hotspot exceeds a critical threshold, then SP routing leads to substantial reductions in capacity to a value close to one simultaneous packet transmission. To overcome this limitation of SP routing, we propose a simple combined SP one-copy routing Hotspot traffic is common in metro ring networks connecting access networks with backbone networks, and these metro rings are also expected to support a mix of unicast, multicast, and broadcast traffic. Shortest path (SP) routing, as employed in the IEEE 802.17 resilient packet ring (RPR), is widely considered for metro rings as it maximizes spatial reuse and, thus, the achievable packet throughput (capacity) for uniform traffic. In this paper, we analyze the capacity of bidirectional optical ring networks, such as RPR, employing SP routing for multicast (nonuniform) hotspot traffic (whereby unicast and broadcast are considered as special cases of multicast). We find that, when the traffic originating at the hotspot exceeds a critical threshold, then SP routing leads to substantial reductions in capacity to a value close to one simultaneous packet transmission. To overcome this limitation of SP routing, we propose a simple combined SP one-copy routing strategy that provides a capacity of at least two simultaneous packet transmissions.strategy that provides a capacity of at least two simultaneous packet transmissions.  In this paper we present an analytical model for the evaluation of access delays and bandwidth efficiency in wavelength-division multiplexing slotted-ring networks where nodes are equipped with one fixed transmitter and several fixed receivers. The system has been analyzed under uniform and non-uniform traffic patterns, for both source and destination stripping schemes. Closed-form and exact expressions for bandwidth efficiency and access blocking probability were obtained. The model is validated by simulations. Traffic grooming is the term used to describe how different traffic streams are packed into higher speed streams. In a synchronous optical network-wavelength division multiplexing (SONET-WDM) ring network, each wavelength can carry several lower-rate traffic streams in time division (TDM) fashion. The traffic demand, which is an integer multiple of the timeslot capacity, between any two nodes is established on several TDM virtual connections. A virtual connection needs to be added and dropped only at the two end nodes of the connection; as a result, the electronic add-drop multiplexers (ADMs) at intermediate nodes (if there are any) will electronically bypass this timeslot. Instead of having an ADM on every wavelength at every node, it may be possible to have some nodes on some wavelength where no add-drop is needed on any timeslot; thus, the total number of ADMs in the network (and, hence, the network cost) can be reduced. Under the static traffic pattern, the savings can be maximized by carefully packing the virtual connections into wavelengths. In this work, we allow arbitrary (nonuniform) traffic and we present a formal mathematical definition of the problem, which turns out to be an integer linear program (ILP). Then, we propose a simulated-annealing-based heuristic algorithm for the case where all the traffic is carried on directly connected virtual connections (referred to as the single-hop case). Next, we study the case where a hub node is used to bridge traffic from different wavelengths (referred to as the multihop case). We find the following main results. The simulated-annealing-based approach has been found to achieve the best results, so far, in most cases, relative to other comparable approaches proposed in the literature. In general, a multihop approach can achieve better equipment savings when the traffic-grooming ratio is large, but it consumes more bandwidth. 