Energy-Efficient Cloud Services over Wavelength-Routed Optical Transport Networks

Elastic optical network (EON) is a promising candidate for the next generation optical transport network because of its high spectrum efficiency and flexible spectrum allocation. However, to migrate from today’s dense wavelength division multiplexing (DWDM) network to EON, optical nodes such as reconfigurable optical add/drop multiplexers (ROADMs) should be replaced with the ones with expensive flexi-grid wavelength selective switches (WSSs). Thus, whether and how today’s optical network will be evolved to EON is still under debate. Meanwhile, with the technical maturity of optical super-channels that transmit bit rates at the level of 1 Tb/s, super-channels are expected to dominate the future optical transport network because of their attractiveness of high spectrum efficiency and superior cost effectiveness. In this paper, we propose a new quasi-coarse wavelength division multiplexing (Quasi-CWDM) optical network architecture that is compatible to today’s WDM network in spectrum operation, while still maintaining the flexibility of adaptation between the bit rate and the transparent reach of an optical super-channel, but not requiring expensive flexi-grid WSSs. Specifically, the Quasi-CWDM optical network employs large fixed frequency grids, whose spacing falls between the traditional CWDM and DWDM, e.g., 200 GHz or 400 GHz. To maintain the flexibility between the bit rate and the transparent reach of an optical super-channel, different modulation formats are chosen according to channel physical distances. To minimize network hardware cost and maximize carried user traffic demand, we develop a mixed integer linear programming (MILP) model and a heuristic algorithm that can efficiently groom upper-layer IP traffic onto the optical layer by optical super-channels. We compare the design based on the Quasi-CWDM network to those based on the DWDM network and the advanced EON. It is found that the proposed Quasi-CWDM network has a much lower hardware cost than the other two types of networks, while achieving spectrum efficiency close to EON.

The need to establish wavelength-routed connections in a service-differentiated fashion is becoming increasingly important due to a variety of candidate client networks (e.g., IP, SDH, ATM) and the requirements for QoS-delivery within transport layers. The multiservice operation changes the way we deal with wavelength-routed paths, as they are now being characterized by manifold properties, such as transmission quality, restoration, network management, and policies. We propose a generic approach to service-differentiated connection accommodation in wavelength-routed networks where, for the network state representation, the supplementary network graphs are defined and referred to as service-specific wavelength-resource graphs. These graphs are used for the appropriate allocation of wavelengths on concatenated physical resources building a wavelength route, along which the necessary transmission quality is achieved and the required management and surveillance functions are provided. By considering twofold wavelength routing metrics, i.e., QoS metrics (service requirements) and resource metrics (quality constraints), these graphs can yield the solution to the QoS-routing problem, i.e., the provision of service-specific guarantees under quality constraints-a feature that is still missing from the existing architectures. The numerical analysis of dynamically reconfigurable multiservice WDM networks is presented for regular network operation as well as for optical network service restoration.

Survivability in waveband switching optical networks: Challenges and new ideas

In this paper, we address the design and management issues in routing a mixture of OC-192 and OC-768 streams in wavelength-routed optical networks. We assume that fiber links in the network are heterogeneous with respect to their transmission capability (i.e., links are designed to handle a given maximum bit-rate imposed by regenerator spacing). We investigate the issues of routing connection demands of various bit-rate requirements in such heterogeneous networks. In this environment, we introduce the routing of multirate traffic (RMT) problem. The RMT problem is informally defined as the process of finding the best routing which maximizes the total bandwidth carried in the network, for a set of sessions, within a given TDM equipment budget. We propose a two-phase optimization scheme (two-phase RMT). This scheme first obtains a basis solution used in routing 40-Gb/s traffic only on OC-768 capable links without the use of TDM equipment. In the second phase, an iterative routing, rerouting, and resource allocation step is used to optimize the total bandwidth carried in the network, while allowing 40-Gb/s traffic to be routed on OC-768 incapable links by the proper installation of TDM multiplexors and demultiplexers at some strategic locations in the network. Numerical results reveal the following: 1) the two-phase RMT optimization algorithm provides substantial savings in terms of both the total TDM equipment installed and number of wavelengths used; 2) noticeable enhancements of the bandwidth utilization and the TDM budget are observed when the route-optimization takes into account the transmission quality of the links; and 3) the use of intermediate TDM multiplexing/demultiplexing functions provides substantial savings, in terms of the total number of channels, over the source-splitting scheme.

Cloud service based on data center (DC) has become an attractive choice for abundant applications. Generally, DCs are distributed at different nodes across a given optical network, and users access DCs through predefined routes. From the perspective of service providers, it is important to offer reliable cloud service while taking service delay and service cost into consideration. In this paper, we study the service routing problem in a given optical network to provide cloud services with high reliability, where failure probability and transmission delay of each link are considered as two coupled parameters. The objective is to minimize the total routing cost and design the access routes for the demands originated from each node. To combine together the corresponding delay and the failure probability of each link, we introduce two cost scaling factors which can be flexibly adjusted to control their relative importance (i.e., the weights). Based on mathematical approximation, a novel method is proposed to compute the failure probabilities of individual service paths. This translates our objective function into a linear expression. Then, we formulate an integer linear program (ILP) to solve the problem. The proposed cloud service routing scheme is validated by extensive numerical experiments.

Current optical transport networks provide high bandwidth through the use of advanced WDM technology, but are difficult to adapt to the different statistical patterns and quality of service (QoS) demands of future traffic. There has been much debate whether the use of dynamically reconfigurable optical networks would have a number of advantages in accommodating the needs of future traffic demands. Dynamic networks would eliminate the need for frequent opto-electronic conversion in current networks, and may save resources through higher utilization and fast adaptation. Different architectures have been proposed to address this problem: Wavelength-routed optical networks (WRON), optical burst switching (OBS), and optical packet-switching (with increasing granularity and speed of reconfiguration). In this paper we investigate whether these architectures are suitable (necessary?) to meet the demands of future traffic, using an analysis focusing on both modeling and experimental aspects.

DWDM optical transport network is the hotspot of the optical communications, the protection and restoration of the multiple wavelength optical transport network is the key technique in the DWDM optical transport network. In this paper, at first we introduce the concept of separate optical layer- the concept of separate optical layer has been demonstrated in some important experimental optical networks- and some advantages of the multiple wavelength optical transport networks, we also compare the DWDM optical transport networks with the SDH networks, put forward some analogies of them. The second, we analyzes the protection and restoration of the multiple wavelength optical networks, we analyze multiple fiber ring networks in detail, we analyze the span protection, line protection and path protection, discuss the advantage and the shortcoming of these different protection mode.

Objectives: The current technologies of wavelength routing and allocation of available for WDM networks are no longer applicable in Elastic Optical Networks (EON), since all their connections are allocated in a fixed manner, as provided for ITU. Therefore, the topic concerning routing and allocation of resources in EON is relevant given the growth projected in web traffic. This survey includes the evolution, main characteristics, and the process of routing and allocation of wavelengths required by EON. Methodology: The processes of allocation of sub-wavelengths and those of super-wavelengths are presented, as well as the multiple storage for different transmission rates and the principle of spectral contiguity. The process of routing and allocation taking OFMD into account is explained. Findings: In this study, we present a survey with routing and allocation techniques of wavelengths that improve the spectral efficiency of EON. Application/Improvements: This survey provides a wide knowledge on the methods to improve the spectral efficiency in EON. Such efficiency can promote an advance in new routing and allocation techniques for the optical transport networks. Keywords: Elastic Optical Networks, EON, Optical Networks, Routing, WDM

This book presents an in-depth deliberation on optical networks in four parts, capturing the past, present, and ensuing developments in the field. Part I has two chapters presenting an overview of optical networks and the enabling technologies. Part II has three chapters dealing with the single-wavelength optical networks: optical LANs/MANs, optical access networks using passive optical network architecture, SONET/SDH, optical transport network and resilient packet ring. Part III consists of four chapters on WDM-based optical networks, including WDM-based local/metropolitan networks (LANs/MANs) using single and multihop architectures over passive-star couplers, WDM/TWDM access networks as an extension of PONs with WDM transmission, WDM metro ring networks covering circuit-switched (using point-to-point WDM and wavelength-routed transmission) plus packet-switched architectures and WDM long-haul backbone networks presenting the offline and online design methodologies using wavelength-routed transmission. Part IV deals with some selected topics in six chapters. The first deals with transmission impairments and power-consumption issues in optical networks, while the next three chapters deal with the survivable optical networks, network control and management techniques, including GMPLS, ASON, and SDN/SDON, and datacenter networks using electrical, optical, and hybrid switching techniques. The final two chapters present elastic optical networks using flexible grid for better utilization of the optical-fiber spectrum and optical packet and burst-switched networks. The three appendices present the basics of the linear programming techniques, noise processes encountered in the optical communication systems, and the fundamentals of queuing theory and its applications in telecommunication networks. (238 words)

The chapter discusses the security of the client signals over the optical network from any wiretapping or loosing. The physical layer of the optical transport network (OTN) is the weakest layer in the network; anyone can access the optical cables from any location and states his attack. A security layer is proposed to be added in the mapping of OTN frames. The detection of any intrusion is done by monitoring the variations in the optical signal to noise ratio (OSNR) by using intelligent software defined network. The signal cryptographic is done at the source and the destination only. The chapter shows how the multi-failure restorations in the multi-domains could be done. A new model is introduced by slicing the multi-domains to three layers to fit the needs of 5G. The results show that the multi-failure restoration improved from 25% to 100%, the revenue from some OTN domains increased by 50%, the switching time enhanced by 50%, the latency reduced from 27 msec to 742 usec, and it will take many years to figure out the right keys to perform the decryption process.

Due to widespread applications and rapid development of cloud computing and Internet services, hyperscale data centers have experienced an unprecedented demand for networking. Data center networks are required not only to handle fast-growing traffic, which doubles almost every one to two years, but also to provide high flexibility and availability to support rapidly changing businesses as well. Therefore, hyperscale data center networks have become one of the main drivers for optical interconnect technologies in recent years. In this article, technologies for scaling optical interconnects for inter-data center interconnects (DCIs) are presented. We first describe hyperscale data center network architectures and requirements, as well as the differences between carrier’s optical transport networks and DCI optical networks, with the main focus on metro-DCI and campus-DCI networks. The scale and fast growth rates of DCI networks require innovations not only in data plane technologies but also in control and management planes as well. In data planes, high-capacity flexible coherent technology, pluggable wavelength-division-multiplexing (WDM) optical transponders, including 100G direct-detection four-level pulse-amplitude modulation (PAM4) and coherent 400ZR/800ZR, and flex-grid and disaggregated reconfigurable optical add-drop multiplexer (ROADM) optical networks are described. Control and management planes are an integral part of optical transport networks and crucial for effectively operating DCI networks. We show that standard protocols, data models, and modular design of a software platform are essential to building a scalable open and disaggregated optical network, which is fundamental to enabling high automation and intelligence in an optical network. An example control and management platform is discussed in detail. With current fiber capacity approaching the nonlinear Shannon limit, challenges to further scale DCI networks and some potential technologies to support ever-increasing traffic growth are discussed at the end.

Mantis: Cloud-based optical network planning and operation tool

An OTN consists of a set of optical network elements connected by a fiber-optic link. OTN can provide the use of transport, multiplexing, routing, management, supervision and resilience of optical channels. OTN (Optical Transport Network) itself is a technology that can increase network bandwidth and reliability by building network functions into optical networks. . An OTN consists of a set of optical network elements connected by a fiber-optic link.

In communication networks, traffic carried over long paths suffers from a higher call blocking probability (CBP) than those carried over short paths. This is a well-known fairness problem. Such a problem becomes more serious in wavelength-routed optical networks (WRONs) due to the wavelength continuity constraint. This paper aims to enhance the fairness characteristic in WRONs by the novel classified alternate routing (CAR) approach. As a foundation of this approach, the first K-shortest paths (KSP) between a designated source/destination node pair in a given network should be obtained simultaneously. This has been studied as the KSP problem in the literature. In this paper, a new loopless deviation (LD) algorithm for solving such a loopless KSP problem will be proposed. It outperforms existing solutions in terms of running time in real-life implementations. In order to measure the fairness characteristic, we first classify all connection requests into categories such as 1-hop traffic, 2-hop traffic, etc., according to the number of minimal hop count between the corresponding source/destination node pair. We then quantify the fairness characteristic by the ratio of the average CBP of each traffic category to that of 1-hop traffic such that CBP ratios with a value closer to 1 are preferred. We will show that such a measure criterion is more precise and robust than existing ones in the literature. Finally, numerical experiments will reveal that the CAR approach outperforms existing fairness enhancement methods when considering the comprehensive performance in terms of the balance between the fairness characteristic and the overall CBP feature.

Network virtualization over WDM and flexible-grid optical networks