Angelo Germoni

Cost Evaluation of Optical Packet Switches Equipped With Limited-Range and Full-Range Converters for Contention Resolution

Two architectures are proposed for a wavelength-division multiplexed optical packet switch equipped with both limited-range wavelength converters (LRWCs) and shared full-range wavelength converters (FRWCs). The FRWCs are used to overcome the performance degradation in terms of packet loss probability due to the use of LRWCs only. Two different sharing strategies of the FRWCs are considered. In the first architecture, a pool of FRWCs is shared among the arriving packets. In the second one, the sharing is only partial and the packets directed to the same output share a same pool of FRWCs. A probabilistic model is proposed to dimension the number of shared FRWCs so that the same packet loss probability of a switch equipped with only shared FRWCs is guaranteed. After introducing a cost model of the converters depending on the conversion range, we show that the architectures may allow a conversion cost savings on the order of 90%.

Multifiber Shared-Per-Wavelength All-Optical Switching: Architectures, Control, and Performance

A new wavelength converter sharing strategy for multifiber optical switches, namely shared-per-wavelength (SPW), which employs wavelength converters with fixed input wavelengths is presented. The aim is to reduce switch costs by using simpler optical components and low complexity space switching matrices. Practical implementations of both the well-known shared-per-node (SPN) and the new SPW schemes are presented, as well as the related scheduling algorithms to manage optical packet forwarding in synchronous scenario. An analytical model to evaluate blocking performance of the SPN architecture is also provided. Results show the accuracy of the model in the range of interest for switch design. The proposed architectures are compared in terms of performance and number of optical components employed. The SPW approach is shown to save a large number of semiconductor optical amplifier gates with respect to the SPN one when the number of fibers per interface is suitably not too high. In these cases, the SPW architecture requires a number of wavelength converters higher than the SPN, but simpler, being their inputs tuned on a single wavelength.

Packet-optical integration nodes for next generation transport networks

The development of a new generation of photonic integrated circuits and the constant progress in integrated electronics (following Moores law) made the realization of a new type of optical transport node possible, by basing it on the concept of a digital photonic switching layer working in coordination with the packet switching layer under the control of a multi-layer control plane. In this paper such a new type of optical transport node is presented, analyzed and implemented in order to better investigate its potential advantages and weaknesses if compared with the conventional all-optical transport nodes and their level of applicability. The new node concept is based on a “vertical” view of packet-opto networks able to face the challenge of growing network capacity while cutting costs and to allow an efficient combination of digital optical networks and packet-opto integrations benefits. Thanks to the use of optical-electrical-optical conversion technology, the wavelength division multiplexed (WDM) layer is provided with the traffic management flexibility and the engineering simplicity of digital transport systems (significant operational expenditures reduction) and with the network cost savings of large-scale photonic integration (capital expenditures reduction). It combines packet and WDM switching technologies where appropriate, with the ability to offload pass-through traffic from the packet layer to the lowest possible layer, so as to reduce costs and power consumption by eliminating unnecessary packet processing (total cost of ownership reduction). The main building blocks are a new digital optical transport based on an integrated packet-opto node that is scalable, flexible and low cost, and multi-layer control and management based on standard generalized multiprotocol label switching and innovative path computation element (PCE) solutions. Thanks to the flexibility of the digital reconfigurable optical add/drop multiplexer, the PCE is able to handle both layers in a very efficient way by selecting the right granularity for traffic grooming and routing. The feasibility has been assessed by a network prototype composed of four nodes produced by Ericsson Research Lab in Pisa and by a simulation analysis.

Packet loss analysis of shared-per-wavelength multi-fiber all-optical switch with parallel scheduling

This paper discusses a multi-fiber all-optical switch which shares wavelength converters for contention resolution. The proposed switch architecture employs fixed-input/tunable-output wavelength converters (expected to be less complex than tunable-input/tunable-output ones). The space switching matrix is modular and simple with respect to switching architectures with different wavelength converters sharing schemes (i.e. shared-per-node architecture). A parallel scheduling algorithm is defined to control optical packet forwarding in a synchronous scenario as well as an analytical model to evaluate packet loss performance. The analytical model is validated against simulation and previous analysis and the results obtained show good accuracy in most cases of interest for optical switch design.

Evaluation of Power Consumption in Low Spatial Complexity Optical Switching Fabrics

In this paper, we propose an analytical model to evaluate the power consumption in the switching fabric of a bufferless shared-per-wavelength (SPW) optical packet switch architecture in which one bank of wavelength converters (WC) is dedicated to each wavelength. We assume that both optical gates and WCs are realized in semiconductor optical amplifier technology. In our evaluation, we account for the power consumption of the current drivers needed to both controlling the used active devices and supplying the thermoelectric coolers. SPW allows for a complexity reduction of the spatial switching matrix that leads to reduced power consumption with respect to other switching architectures. Results show the effectiveness in terms of consumed power of the considered architecture with respect to the shared-per-node reference architecture, where a fully sharing strategy of WCs is adopted. The main results show that SPW allows us to reduce the power consumption in the order of 26% for offered traffic equal to 0.6. The obtained results also show how the fabric switching of the SPW optical packet switch consumes much less power per gigabits per second carried than the one of a typical commercial core router.

Cost Evaluation of Optical Packet Switches Using Both Limited-Range and Full-Range Converters for Contention Resolution

An architecture is proposed for a wavelength division multiplexed (WDM) optical packet switch equipped with both limited range wavelength converters (LRWCs) and shared full range wavelength converters (FRWCs). The FRWCs are used to overcome the performance degradation in terms of packet loss probability due to the use of LRWCs only. A probabilistic model is proposed to dimension the number of shared FRWCs so that the same packet loss probability of a switch equipped with only shared FRWCs is guaranteed. After introducing a cost model of the converters depending on the range conversion, we show that the architecture may allow conversion cost saving in the order of 85%.

Loss Analysis of Multiple Service Classes in Shared-per-Wavelength Optical Packet Switches

Management of quality of service in optical packet switches equipped with fixed input, tunable output wavelength converters is described. This kind of switch is considered with the aim to keep switch cost low by employing simple shared optical components and low-complexity space switching matrices. In particular, differentiation among classes of service in terms of loss performance for bufferless switches is addressed. The functionalities described refer to the high-speed multiservice networking context foreseeable for the future Internet. A switch control algorithm to manage service classes in a slotted multiplexing context is described. An analytical model to evaluate the loss probability of each class is developed and validated against a simulation and is used to prove the effectiveness of the quality-of-service approach. Numerical results show that the proposed scheme achieves basic class isolation as needed in core network optical packet switches.

Integration of planning and control plane in packet optical multilayer network

An integrated solution relying on a centralized management and a distributed control plane is presented for packet optical networks. Simulations results, based on realistic network, traffic and node modeling, show up to 42% CapEx saving.

Performance evaluation of OTDM/WDM networks in dynamic traffic scenario

In this paper we propose a new solution for the Routing, Wavelength and Time-Slot Assignment (RWTA) problem in a dynamic scenario. The novel aspect of this paper is that we consider nodes performing Time-slot Add-Drop directly in optical domain. The Add-Drop capabilities allow for a better network utilization in terms of blocking probability. In particular we define two heuristics, the Add-Drop static and the Add-Drop adaptive, able to exploit Add-Drop capabilities when a new connection request arrives. We compare our solution with the classical Super-Lightpath one, where Optical Time Division Multiplexing (OTDM) is not performed, proving that both the Add-Drop heuristics have always better performance.

Multilayer control for packet-optical networks [invited]

This paper describes a novel multilayer (ML) path computation element (PCE) architecture based on a hybrid approach. Such a method operates in all network life cycles, optimizing both the design and the operative phases. The hybrid PCE is based on combined non-realtime and real-time operation and is able to integrate control and management functions. This architecture results in a reduction of overprovisioning during network design while guaranteeing availability of traffic by using control-plane-driven dynamic recovery schemes. It introduces advanced control functionality into the network, providing an easy-to-integrate solution. To fully exploit the control plane capabilities, a new architecture of colorless, directionless, and contentionless reconfigurable optical add/ drop multiplexers and its related cost model are also presented. The solution has been assessed by simulations on the Spanish backbone network of Telefonica. The simulation analysis demonstrates the good performance of the proposed ML solution. The reduction of overprovisioning allows a capital expenditure saving of up to 46% with respect to a single-layer approach without any effect on the level of survivability of the traffic, thanks to new ML recovery schemes.