The 15 papers in this special issue focus on traffic engineering for multi-layer networks. The papers can be roughly divided into the following three groups: 1) New Approaches to Traffic Engineering, 2) Multi-layer Survivability, and 3) Specific Issues. Some of the specific issues include optimal topology design, multicast flow aggregation, load balancing, traffic grooming, and Ethernet-based technology.

In this contribution, the problem of download time minimization, by considering channel state, is solved for application scenario where the downlink channel is slotted and continuous-state, while the resulting conveyed throughput is measured by any desired increasing concave rate-function. Specifically, the optimal energy-allocation policy minimizing the download-time is found and its performance is compared against that of a basic on-off type heuristic scheduler for some Rayleigh-faded multi-antenna downloading systems of practical interest

Next-generation network infrastructure should support different services and several levels of quality of service (QoS) and resilience. The main requirements for such multiservice networks are flexibility, effective utilization of network resources, and ability to react to traffic demand changes with time. These requisites lead to the fact that next-generation networks should, to some extend, be "self-adapting," to cope with the need of promptly reacting to traffic demand changes, in an effective way, while taking into account the different requirements in terms of QoS. This paper sketches the reference network scenario and discusses the subject of self-adapting networks, attempting to focus on the key issues that need to be solved to realize future infrastructures. As a relevant example, this paper briefly reports a system developed by the authors' laboratory that implements a traffic engineering solution able to fulfill the mentioned requirements. This system could be regarded as a first concrete step toward the realization of self-adapting networks. In addition, some relevant results that were obtained either by simulation or by experiments on a real test bed are reported to discuss the main characteristics of such a system and assess the feasibility of the concept. Finally, the paper reviews the main hot issues that need to be addressed, in the authors' opinion, by the international research community.

This paper presents an integrated traffic engineering (TE) system for new generation multilayer networks based on the generalized multiprotocol label switching (GMPLS) paradigm, and reports the performance analysis of such a system. The proposed TE system aims at dynamically reacting to traffic changes and, at the same time, fulfilling quality of service (QoS) requirements for different classes of service. The proposed solution consists of a hybrid routing approach and a bandwidth management strategy. The former makes use of both off-line and on-line methods to accommodate traffic requests. The latter, based on an "elastic" use of the bandwidth, allows the handling of different priorities among data flows, possible preemptions, and rerouting. The proposed TE permits the accommodation of the largest amount of traffic, while guaranteeing good performance to mission-critical services. The main building blocks and the operations of the system are reported and the major advantages are discussed. The performance of the proposed system are compared with the ones relating to a reasonable alternative system based on overprovisioning, to highlight its advantages of in terms of traffic volume that can be accommodated for a given network infrastructure.

This paper reports an analysis of the performance of wireless broadband communication systems employing fiber-optic links to connect the base station with the control station. Rainfall attenuation on the radio link, and nonlinear distortions arising from the direct modulation of the laser source, besides the noise contributions coming out from both the optical transmitter and receiver, are considered in the analysis. As far as the radio link is concerned, the outage probability, due to the rainfall attenuation, is recounted for relevant cases; while, concerning the optical link, several carrier-to-noise ratio curves versus the optical modulation index of the channels are reported, varying different system parameters. With respect to the previous literature, a complete analysis of the optical link performance, in this type of systems, has been accomplished by taking into account, simultaneously, all the effects influencing the performance.

An analysis of transmission performance of optical transport networks employing two different types of wavelength conversion (based on four wave mixing and cross phase modulation) and adopting two different node architectures is reported. The performance is evaluated by means of a system modeling which allows one to consider physical phenomena occurring during transmission and all the important impairments that introduce system penalties. The limits of these kinds of network are investigated and the main features are reported. The analysis reveals that both the types of converters can be employed with different features and limitations, according to the considered architecture. An example of geographical network is discussed and its simulated transmission performance is reported.

The authors analyze the use of all optical wavelength conversion in the optical layer of a high-capacity transport network and compare different technological solutions. The analysis is based on the evaluation of the transmission performance of a generic signal path through the network. At least two technologies have been discovered allowing the realization of all-optical wavelength converters suitable for use in the considered application, providing high performance. In particular, for networks covering long distances, wavelength conversion based on four-wave-mixing in semiconductor amplifiers seems to be a very interesting solution.