• Transport Research
• Journal of Lightwave Technology close

This paper addresses the possibility of using traffic engineering in the wavelength domain as a way to improve the performance of optical burst-switched (OBS) networks. With that aim, we detail a heuristic traffic engineering strategy that determines the order by which the ingress nodes of the network should search for an available wavelength for burst transmission, in order to minimize the probability that data bursts going through overlapping paths reach a common fiber link using the same wavelength. By means of network simulation, it is shown that the proposed traffic engineering strategy outperforms the existing strategies in reducing burst loss in OBS networks. This trend holds for core nodes with different degrees of wavelength conversion, ranging from the absence of wavelength converters to the use of dedicated full-range wavelength converters. More specifically, it is shown that using only traffic engineering in the wavelength domain can dramatically reduce burst loss in networks without wavelength conversion or alternatively it can reduce the number of wavelength converters in networks based on shared wavelength conversion. The simulation results also show that by combining traffic engineering in the wavelength domain with the use of the inexpensive electronic buffers at the ingress nodes, the performance of OBS networks with dedicated full-range wavelength converters can be further improved at the expense of a slight increase in the burst transfer delay.

In wavelength-routed networks based on a GMPLS control plane, the resource reservation protocol with traffic engineering extensions (RSVP-TE) allows to establish end-to-end lightpaths. The resource reservation can be blocked due to lack of available resources (forward blocking) or due to resource contentions (backward blocking). In wavelength-routed networks, the backward blocking is the predominant blocking contribution, when traffic load is low or highly-dynamic and when lightpath restoration takes place. To reduce the backward blocking, the paper proposes two label preference (LP) schemes compliant with RSVP-TE message exchanges. LP schemes provide the destination node with a label identifying the preferred wavelength to reserve. The preferred label is computed in a distributed way during the forward signaling phase, with the objective of assigning disjoint wavelengths to reservation attempts that may contend the resources. Simulation results demonstrate that, compared to other schemes, LP schemes are effective in reducing the backward blocking during both lightpath provisioning and restoration, without negatively impacting the forward blocking.

From the network layer perspective, the problem of burst losses is one of the most challenging problems which restrain the development of optical burst switching (OBS) networks. Indeed, OBS is a buffer-less technology and the consequent lack of guarantees for data delivery may affect significantly the quality of service (QoS) perceived by end users. To overcome these obstacles, dedicated network mechanisms and design methods are required for QoS provisioning in the network. With this end in view, in this paper, we present a traffic engineering (TE) approach to support the end-to-end traffic delivery with absolute QoS guarantees, in terms of burst losses, in an OBS network. We focus on the establishment of explicit routing paths and minimum allocation of wavelength resources in network links under the requirement that certain absolute level of burst loss probability for a given set of traffic demands is guaranteed. In this paper, we call such an off-line problem the virtual topology (VT) design problem. Since the VT design problem is NP-complete, as an alternative to the mixed integer linear programming formulation, we develop a local search heuristic algorithm to solve it. Moreover, we focus on a dynamic OBS network scenario, where the offered traffic is subject to a change. In this context, we propose an on-line VT maintenance mechanism that is responsible for traffic admission control and adaptation of the VT to traffic changes. Eventually, proposed algorithms and mechanisms for the TE-driven end-to-end QoS approach are verified both numerically and by means of network simulations for a number of network scenarios.

Shortest path algorithms such as shortest path first (SPF) and constrained shortest path first (CSPF) are widely used in online traffic engineering where connections need to be set up one at a time as connection requests arrive sequentially. We propose an approach, called design-based routing (DBR), whereby optimized paths computed offline are used to guide online path setups. Offline path computation in generalized multiprotocol label switching (GMPLS) networks does not pose a significant challenge since optical core or metro networks typically consist of a few dozen to hundreds of nodes compared to hundreds to more than one thousand nodes in pure data networks. DBR takes advantage of available demand information based on customer prescriptions, traffic projections, and historical measurements to build an approximate traffic demand matrix for path optimization. By means of simulation, we perform comparative evaluations of opaque GMPLS networks under static and dynamic connections with different protection modes. The results indicate that DBR outperforms SPF and CSPF under a wide range of operating conditions and is robust to inaccuracies in the estimation of the traffic demand matrix. We then construct routing schemes with resource management and online measurement. The simulation results indicate that resource management provides an effective way to mitigate greed inherent in CSPF, and online measurement provides an effective way to improve DBR performance when the traffic demand information used in the design of DBR paths is different from the actual traffic demand.

Network operators are evolving their optical transport networks in order to make them cost effective. In some scenarios, this means considering adopting software-defined networking principles along with open and standard interfaces, leveraging the underlying hardware programmability while, at the same time, considering the benefits of (partial) disaggregation, in view of the potential benefits of decoupling terminal devices from the line systems or of separating the hardware from the controlling software. In this evolution, operators often segment their networks into domains. Reasons include the need to scale, or confidentiality and/or vendor interoperability constraints. Additionally, the need to virtualize the (multi-domain) transport network has emerged as a key requirement to support functions such as network slicing and partitioning, and to empower end users to control their allocated partitions, enabling new business models related to multi-tenancy. In this context, several standards-defining organizations have been working on architectures, interfaces, and protocols to support requirements, such as the Abstraction and Control of Traffic Engineering Networks of the Internet Engineering Task Force, known as ACTN. In this article, we experimentally validate a control plane architecture for multi-domain disaggregated transport networks that relies on the deployment of network elements compliant with the OpenROADM multi source agreement device model. We demonstrate the abstraction and control of such networks in line with the ACTN framework and we show the applicability of the approach with a proof-of-concept testbed implementation.

This paper reports a summary of the joint research activities on Optical Core Networks within the e-Photon-ONe+ project. It provides a reasonable overview of the topics considered of interest by the European research community and supports the idea of building joint research activities that can leverage on the expertise of different research groups. Thisworkwas supported by the e-Photon/ONe+ and BONE (“Building the Future Optical Network in Europe”) projects funded by the European Commission through the 6th and 7th ICT-Framework Programme