Architectures and performance of AWG-based optical switching nodes for IP networks

In order to support the continuous growth of transmission capacity demand, optical packet switching technology is emerging as a strong candidate, promising to allow fast dynamic allocation of wavelength-division multiplexing (channels, combined with a high degree of statistical resource sharing). This work addresses the design of optical switch architectures, based on previous proposals available in the technical literature that use an arrayed waveguide grating (AWG) device to route packets. Since the port number of currently available AWGs is a limiting factor, we propose two new modified structures which better exploit the switching capability of this component in the wavelength domain. Since a limited hardware complexity is a key requirement for all-optical switches, due to the high cost of optical components, these different node configurations are compared in terms of complexity. Traffic performance of these new structures in a full optical packet switching scenario is also examined.     

Multilayer Protection with Availability Guarantees in Optical WDM Networks

Survivability is a key concern in modern network design. This paper investigates the problem of survivable dynamic connection provisioning in general telecom backbone networks, that are mesh structured. We assume differentiated services where connections may have different availability requirements, so they may be provisioned differently with protection (if needed) based on their availability requirements and current network state. The problem of effectively provisioning differentiated-service requests, that has been widely investigated for connections routed at the physical layer, assumes peculiar features if we consider sub-wavelength requests at the logical layer that have to be protected (or more generically, whose availability target has to be guaranteed), but also have to be groomed for an efficient use of network resources. An integrated multilayer approach is necessary that considers requirements and grooming of connections at the logical layer as well as their routing and availability at the physical layer. Joint availability-guaranteed routing and traffic grooming may lead to a negative interaction, since the objective of the first problem (guaranteeing a given level of availability to the connections) clashes with the objective of the other problem (minimizing resource consumption). For a multilayer WDM mesh network, we propose new multilayer routing strategies that perform effective availability-guaranteed grooming of sub-wavelength connections. These strategies jointly considers connection availability satisfaction and resource optimization and are developed under two different practical hypotheses: guaranteed target, i.e., a connection is routed only if its availability target is satisfied, and best-effort target, a connection is always routed and, when the availability target cannot be guaranteed, the path with the best possible availability is provisioned. Numerical results are reported and discussed for the two approaches mentioned above. In both cases, the results show high effectiveness of our provisioning strategy.     

Performance evaluation of large capacity broadcast-and-select optical crossconnects

In this work, two bufferless high capacity broadcast-and-select optical switching node architectures are presented and their performance is evaluated. The architectures are modular permitting the expansion from basic to complex structures by adding new blocks/components in a gradual way, enhancing at the same time the corresponding network functionality. The blocking performance is assessed and scheduling algorithms are proposed to solve contention for a single node. Finally, physical layer modeling is carried out in order to investigate node scalability and node cascadeability. Overall, the proposed solutions are offering modularity, transparency to switching technology, graceful evolution and high performance at an affordable cost.     

Design and cost performance of the multistage WDM-PON accessnetworks

The advantages of employing passive optical architectures in the access network have been largely recognized. Particularly, recent developments in optical technologies have made the realization of wavelength division multiplexing passive optical networks (WDM PONs) feasible and cost-effective. These networks are more future-proof than conventional PONs, thanks to their intrinsic optical transparency and their extremely high transmission capacity. A very useful optical routing device, called waveguide grating router, is the basic building-block of new PON architectures capable of connecting a large number of users or to improve the use of the optical bandwidth. In this paper, we analyze the connectivity of WDM PONs composed of multiple stages of WGR devices. A design tool is also presented which is able to easily evaluate the connectivity functions of complex WDM PONs. The feasibility of these architectures is discussed by considering the costs and the technological limitations on the optical components     

Routing Algorithms in WDM Networks under Mixed Static and Dynamic Lambda-Traffic

Dynamic traffic is becoming important in WDM networks. In the transition towards full dynamic traffic, WDM networks optimized for a specific set of static connections will most likely also be used to support on-demand lightpath provisioning. Our paper investigates the issue of routing of dynamic connections in WDM networks which are also loaded with high-priority protected static connections. By discrete-event simulation we compare various routing strategies in terms of blocking probability and we propose a new heuristic algorithm based on an occupancy cost function which takes several possible causes of blocking into account. The behavior of this algorithm is tested in well-known case-study mesh networks, with and without wavelength conversion. Moreover, Poissonian and non-Poissonian dynamic traffics are considered.     

Design of Protected WDM Wheel Networks under Various Traffic Conditions

Wavelength-division-multiplexing networks dimensioned for static connections could be used to accommodate an unpredictable increase of lightpath requests. We analyze the problem of the new carriers to deploy networks that provide them flexibility to deliver long-lived lightpaths on demand without capacity upgrade of the existing infrastructures. We investigate the influence of the connectivity factor in both the initial optimization and on the probability of accommodating the traffic expansion. We consider multifiber WDM wheel networks, a sequence of regular ring-to-mesh architectures, under various static traffic conditions. The optimization is carried out by means of a heuristic aimed at minimizing the number of fibers. The maximum allowable traffic scaling factor is evaluated by simulations with different initial network states that have already accommodated the static traffic.     

Reuse partitioning in cellular networks with dynamic channel allocation

Great interest in recent years has been devoted to mobile communications. The research effort has been directed to increasing the capacity of radio systems by applying space reuse techniques. Higher efficiency in the usage of the available frequency spectrum can be obtained either by reducing the cell size, thus requiring the provision of new base stations, or by reusing the available spectrum more efficiently without cell size reduction. In this paper we present a dynamic frequency allocation algorithm for cellular networks that exploits a given reuse pattern. The performance of the proposed scheme, in terms of blocking probability, is evaluated by means of computer simulations both when the position of the mobiles remains unchanged and when mobility is taken into account, under both uniform and hotspot traffic. The numerical results show that the capacity of the proposed scheme is sensibly higher than that of a dynamic channel allocation without reuse partitioning. The effects of both user mobility and reuse partitioning on the signalling load are also considered.     

Performance evaluation of a Batcher-banyan interconnection networkwith output pooling

A Batcher-banyan interconnection network that overcomes the limitation of switch throughput and unfair allocation of bandwidth is proposed, and its performance is evaluated. The throughput limitations of the interconnection network are substantially reduced by defining pools of outputs, in which groups of outputs that offer the same service behave each as a set of servers sharing a single waiting list. Through a careful system design and a suitable priority scheme, the servers in a set can be evenly allocated to the users requesting service from the inputs of the interconnection network. Three different solutions are proposed for the allocation of the output channels within a pool to those users requesting the same pool. Extensive computer simulation was used to evaluate the overall packet delay performance and the degree of fairness provided by each of these solutions