Optical WDM Networks

From Static to Elastic Networks

Devi Chadha

• Publisher: Wiley-IEEE Press
• Year: 2019
• ISBN:
  9781119393344
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Waves & Wave Mechanics

Provides a comprehensive and updated account of WDM optical network systems

Optical networking has advanced considerably since 2010. A host of new technologies and applications has brought a significant change in optical networks, migrating it towards an all-optical network. This book places great emphasis on the network concepts, technology, and methodologies that will stand the test of time and also help in understanding and developing advanced optical network systems.

The first part of Optical WDM Networks: From Static to Elastic Networks provides a qualitative foundation for what follows—presenting an overview of optical networking, the different network architectures, basic concepts, and a high-level view of the different network structures considered in subsequent chapters. It offers a survey of enabling technologies and the hardware devices in the physical layer, followed by a more detailed picture of the network in the remaining chapters. The next sections give an in-depth study of the three basic network structures: the static broadcast networks, wavelength routed networks, and the electronic/optical logically routed networks, covering the characteristics of the optical networks in the access, metropolitan area, and long-haul reach. It discusses the networking picture; network control and management, impairment management and survivability. The last section of the book covers the upcoming technologies of flex-grid and software defined optical networking.

• Provides concise, updated, and comprehensive coverage of WDM optical networks
• Features numerous examples and exercise problems for the student to practice
• Covers, in detail, important topics, such as, access, local area, metropolitan, wide area all-optical and elastic networks
• Includes protocols, design, and analysis along with the control and management of the networks
• Offers exclusive chapters on advance topics to cover the present and future technological trends, such as, software defined optical networking and the flexible grid optical networks

Optical WDM Networks: From Static to Elastic Networks is an excellent book for under and post graduate students in electrical/communication engineering. It will also be very useful to practicing professionals in communications, networking, and optical systems.

1
Introduction to Optical Networks

1.1 Introduction

Any technological development is always driven by the need and demand of the changes in society. The rapid evolution of communication networks from the basic telephone network to the present high‐speed large area networks has come with the social need of people to communicate among themselves, with the increasing user demands for new applications, as well as advances in enabling technologies. The fast changes in the present‐day telecommunication networks are also driven by the user's need to remain connected anytime and all the time, anywhere and everywhere in the world. The new applications, i.e. multimedia services, video‐conferencing, interactive gaming, Internet services, and the World Wide Web, all demand very large bandwidths. Besides this, the user wants the unifying network underneath to be reliable, give the best services, and be cost‐effective as well.

What we need today, therefore, is a communication network with high capacity and low cost, that is fast, reliable, and able to provide a wide variety of services from dedicated to best‐effort services. The available transmission media best suited to meet most of these requirements is optical fiber. Besides having enormous bandwidth in terahertz (~10¹² Hz), optical fiber has low loss and cost. It is lightweight, with strength and flexibility, and is immune to electromagnetic interference and noise. It is secure and has many more characteristics to make it an ideal high‐speed transmission line, therefore optical fiber is most suitable to meet the traffic requirements in today's communication network. The enormous quantity of optical fiber laid throughout the world by the end of twentieth century is the foundation of the information super highway of optical network with huge bandwidth today.

1.1.1 Trends in Optical Networking

In order to increase the capacity of point‐to‐point links, optical fibers first replaced the coaxial and two‐wire transmission lines in the existing communication networks. The capacity of the optical links in the network was further increased by using wavelength division multiplexing (WDM) in the laid fiber, thus having several wavelength channels carrying multiple data streams in a single fiber. But all the switching and routing operation in the network still remained in the electronic domain. In the real sense we do not define this network as an all‐optical network. An all‐optical network is the high‐capacity telecommunication network which uses optical technology and components not only to provide large capacity optical fiber links for information transmission but also to do all the networking operations, such as switching and routing (i.e. facilitation of the correct and suitable path) of the signals on the required path, grooming of the low bit rate traffic signals to higher bit rate for better utilization of the enormous capacity of the fiber, and control and restoration functions in the network at the optical level in case of any failure in the network. The operation of the network at the optical or wavelength granularity level has many advantages. As an example, when a single wavelength carries a large number of independent connections and a failure occurs in a fiber cable, it is operationally much simpler to restore services by routing and processing an individual wavelength than to reroute each connection individually. Besides, optical switching functions consume much less power and have lower heat dissipation and footprint compared with their electronic counterparts. With the present optical technology, it is still not possible to achieve all these functions cost‐effectively with ease. Hence, both optical and electronic devices are used, which makes the optical network not purely optical. These networks are indeed hybrid in nature at present, using both optical and electronic technology.

The communication network, which once supported telephone voice traffic only, now carries more data traffic supporting high‐speed multimedia services. At the physical infrastructure level, the available optical components in the optical network can now support traffic at multiple speeds ranging up to tera‐bits/sec (Tbps), with each fiber carrying a large number of wavelengths in the WDM systems. Also, along with the optical component infrastructure, the networks are becoming more flexible and agile due to the adoption of intelligent algorithms and protocols for networking, and therefore the network can now respond to new applications and demands with ease. The trend in optical networks is now toward SDON (software defined optical networking) to facilitate programmability of network operations to further increase agility and to provide users with more control over networking functions, thereby resulting in flexibility in the deployment of new services and protocols, better network utilization, QoS (quality of service), higher revenue generation from the flexibility added in the network, and the user managing the network according to his/her requirements. There is a paradigm shift in optical networking now with SDON, which is a fast‐evolving technology [1–4].

In the rest of the chapter we will give a brief overview of the optical networks and an introduction to the technologies, terminologies, and parameters involved. In order to have some understanding of the functionalities of different types of networks used, somewhat detailed stratification of a generic network is discussed, hoping for an easier understanding of the networks in subsequent chapters where these will be discussed in detail.

1.1.2 Classification of Optical Networks

On the basis of geographical reach, the telecom network can be subdivided in three categories: the access and local area network (LAN), the regional metropolitan area networks (MANs), and the backbone wide area network (WAN). This is shown in Figure 1.1.

Figure 1.1 Classification of the communication network on the basis of reach.

Any two distant users in the access network communicate with each other through the switch/router (or exchange) to the rest of the network infrastructure. The access network can have a span of up to 20 km or so. The access network needs to be cost‐effective as the cost has to be shared among a smaller number of individual users who are connected through it to the shared communication network underneath. The present‐day high‐speed optical solution to the access part is with passive optical networks (PONs), with many variants of the Ethernet passive optical network (EPON), gigabit passive optical network (GPON), and WDM PON, etc. The other lower speed access networks are provided by wireless (WiMax, Wi‐Fi), cable modems, digital subscriber lines (DSLs), higher speed lines (T1/E1), etc. We discuss the access networks in detail in Chapter 4.

The metro network covers distances of a few kilometers to hundreds of kilometers. The metro network aggregates the traffic from the access networks. The technologies used in metro networks are a lot different from those in access networks. Metro networks generally have a ring physical architecture using the legacy Synchronous Optical NETworking (SONET)/synchronous digital hierarchy (SDH), asynchronous transfer mode (ATM), or optical transport network (OTN) networks. A node (router) of the ring or mesh collects or distributes the traffic of the access network connected to the ring while the hub node ...