t is widely recognized that traffic will be more and more dominated by Internet-based services, with respect to traditional voice traffic [1] , thanks to increased adoption of high-speed access technology and migration of more and more services toward the Internet Protocol (IP). Voice traffic is still growing, but at a slower rate. As a result, two main factors are of critical importance in the development of new-generation networks (NGNs): the sheer quantity of traffic is growing rapidly, and the type of traffic is changing. As a result the telecommunications world is evolving strongly toward challenging scenarios: the convergence of the telecom and datacom worlds into the infocom era is becoming a reality. New infrastructures have to be compliant with such an infocom network scenario. In practice this means that network infrastructure has to be multiservice, that is, able to support several types of traffic with different requirements in terms of quality of service (QoS) [2] . Since IP traffic will be the dominant portion, network infrastructures must take into account its characteristics. Two main attributes typify Internet traffic: • Its self-similar nature • Asymmetry of the data flows As a whole, Internet traffic is not easily predictable and stable as is traditional voice traffic. Consequently, a basic requirement arises for new-generation infrastructure: flexibility and ability to react to traffic demand changes with time. Another key issue relates to the fact that even though Internet traffic is becoming dominant, it does not generate revenue as do valuable voice services. This, practically, means that if the network were upgraded by adding bandwidth and expanding infrastructure in proportion to the amount of data traffic increase, the revenues would be smaller than the cost. Thus, in order to be profitable, Internet service providers (ISPs) and network carriers must both reduce costs by means of an effective use of network resources and increase revenues by offering multiservice and QoS capabilities. Moreover, the migration of all services over IP, including the real-time ones, requires guaranteeing QoS for a subset of services that should be comparable to those provided by telecom-based networks nowadays. As a result, several requirements come out for NGNs: provide fast provisioning, handle traffic fluctuations and growth, handle the QoS to honor service level agreements (SLAs) for different types of traffic in terms of bandwidth, delay, packet loss, or any other quality requirements, and offer multiservice capabilities. The challenging task for established network operators is how to migrate their voice network toward the new-generation infrastructure, while minimizing the costs of the transition and taking early advantage of the benefits offered by next-generation networks. Multiprotocol label switching (MPLS) addresses these issues by means of traffic engineering (TE) mechanisms that allow the advantages of flexibility and performance in conjugating layers 3 and 2, respectively [3] . The challenge for NGNs consists of extending such flexibility and efficiency to other layers of the network, such as synchronous digital hierarchy/synchronous optical network (SDH/SONET) and wavelength-division multiplexing (WDM) in order to consider even non-packet-based forwarding planes. Thanks to the MPLS extension by means of generalized MPLS (GMPLS), the key ingredients to perform efficient TE for different technologies are available [4] . However, a feasible solution that is able to use such ingredients is still not consolidated. Actually, TE should provide the network with the possibility to dynamically control traffic data flows, to optimize the availability of resources, to choose routes for traffic flows while taking into account traffic loads and network state, and to move traffic flows toward less congested paths. All these functions should be performed handling different network layers and technologies. This article describes a pragmatic network solution that  This article discusses a novel approach for realizing traffic engineering in the framework of new-generation multilayer networks based on the GMPLS paradigm. In particular, the proposed traffic engineering system is able to dynamically react to traffic changes while at the same time fulfilling QoS requirements for different classes of service. The proposed solution consists of a hybrid routing approach, based on both offline and online methods, and a novel bandwidth management system that handles priority, preemption mechanisms, and traffic rerouting in order to concurrently accommodate the largest amount of traffic and fulfill QoS requirements. The bandwidth resources of the network are effectively exploited by means of "elastic" utilization of the bandwidth. The main building blocks and operations of the system are reported, and the major advantages are discussed.
In REF , a traffic engineering system is presented considering the multilayer approach and taking into account both methods of routing, off-line and on-line.
A traffic engineering system for multilayer networks based on the GMPLS paradigm
Network, IEEE
Computer Science