Wavelength switched optical network

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Wavelength Switched Optical Network with two established lightpaths Wson-network.png
Wavelength Switched Optical Network with two established lightpaths

Wavelength switched optical network (WSON) is a type of telecommunications network.

Telecommunications network network to enable telecommunication between different terminals

A telecommunications network is a collection of terminal nodes in which links are connected so as to enable telecommunication between the terminals. The transmission links connect the nodes together. The nodes use circuit switching, message switching or packet switching to pass the signal through the correct links and nodes to reach the correct destination terminal. Each terminal in the network usually has a unique address so messages or connections can be routed to the correct recipients. The collection of addresses in the network is called the address space. Examples of telecommunications networks are:

A WSON consist of two planes: the data and the control planes. The data plane comprises wavelength-division multiplexing (WDM) fiber links connecting optical cross-connect (OXCs) through a comb of several tens of wavelength channels, with typical data rates of 10 or 40 Gbit/s. Optical end-to-end connections (i.e., lightpaths) are established in the optical domain and switched by OXCs at the wavelength granularity. [1]

Wavelength-division multiplexing

In fiber-optic communications, wavelength-division multiplexing (WDM) is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths of laser light. This technique enables bidirectional communications over one strand of fiber, as well as multiplication of capacity.

An optical cross-connect (OXC) is a device used by telecommunications carriers to switch high-speed optical signals in a fiber optic network, such as an optical mesh network.

A lightpath in optical networks is a path between two nodes between which light passes through unmodified.

The dynamic provisioning and maintenance of lightpaths is managed by the control plane. The control plane is implemented on a separate network and typically employs one network controller for each node in the data plane, as shown in the figure. The Generalized Multi-Protocol Label Switching (GMPLS) protocol suite, the de facto standard control plane for WSONs proposed by the IETF, is composed of three protocols. [2]

Generalized Multi-Protocol Label Switching (GMPLS) is a protocol suite extending MPLS to manage further classes of interfaces and switching technologies other than packet interfaces and switching, such as time division multiplexing, layer-2 switching, wavelength switching and fiber-switching.

Internet Engineering Task Force organization

The Internet Engineering Task Force (IETF) is an open standards organization, which develops and promotes voluntary Internet standards, in particular the standards that comprise the Internet protocol suite (TCP/IP). It has no formal membership or membership requirements. All participants and managers are volunteers, though their work is usually funded by their employers or sponsors.

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Synchronous optical networking

Synchronous optical networking (SONET) and synchronous digital hierarchy (SDH) are standardized protocols that transfer multiple digital bit streams synchronously over optical fiber using lasers or highly coherent light from light-emitting diodes (LEDs). At low transmission rates data can also be transferred via an electrical interface. The method was developed to replace the plesiochronous digital hierarchy (PDH) system for transporting large amounts of telephone calls and data traffic over the same fiber without the problems of synchronization.

Single-mode optical fiber

In fiber-optic communication, a single-mode optical fiber (SMF) is an optical fiber designed to carry light only directly down the fiber - the transverse mode. Modes are the possible solutions of the Helmholtz equation for waves, which is obtained by combining Maxwell's equations and the boundary conditions. These modes define the way the wave travels through space, i.e. how the wave is distributed in space. Waves can have the same mode but have different frequencies. This is the case in single-mode fibers, where we can have waves with different frequencies, but of the same mode, which means that they are distributed in space in the same way, and that gives us a single ray of light. Although the ray travels parallel to the length of the fiber, it is often called transverse mode since its electromagnetic oscillations occur perpendicular (transverse) to the length of the fiber. The 2009 Nobel Prize in Physics was awarded to Charles K. Kao for his theoretical work on the single-mode optical fiber.

Optical burst switching (OBS) is an optical networking technique that allows dynamic sub-wavelength switching of data. OBS is viewed as a compromise between the yet unfeasible full optical packet switching (OPS) and the mostly static optical circuit switching (OCS). It differs from these paradigms because OBS control information is sent separately in a reserved optical channel and in advance of the data payload. These control signals can then be processed electronically to allow the timely setup of an optical light path to transport the soon-to-arrive payload. This is known as delayed reservation.

A passive optical network (PON) is a telecommunications technology used to provide fiber to the end consumer, both domestic and commercial. A PON's distinguishing feature is that it implements a point-to-multipoint architecture, in which unpowered fiber optic splitters are used to enable a single optical fiber to serve multiple end-points. The end-points are often individual customers, rather than commercial. A PON does not have to provision individual fibers between the hub and customer. Passive optical networks are often referred to as the "last mile" between an ISP and customer.

The routing and wavelength assignment (RWA) problem is an optical networking problem with the goal of maximizing the number of optical connections.

ASON is a concept for the evolution of transport networks which allows for dynamic policy-driven control of an optical or SDH network based on signaling between a user and components of the network. Its aim is to automate the resource and connection management within the network. The IETF defines ASON as an alternative/supplement to NMS based connection management.

ASTN allows traffic paths to be set up through a switched network automatically. The term ASTN replaces the term ASON and is often used interchangeably with GMPLS. This is not completely correct as GMPLS is a family of protocols, but ASON/ASTN is an optical/transport network architecture. The requirements of the ASON/ASTN architecture can be satisfied using GMPLS protocols developed by the IETF or by GMPLS protocols that have been modified by the ITU. Furthermore, the GMPLS protocols are applicable to optical and non-optical networks, and can be used in transport or client networks. Thus, GMPLS is a wider concept than ASTN.

Optical networking is a means of communication that uses signals encoded onto light to transmit information among various nodes of a telecommunications network. They operate from the limited range of a local-area network (LAN) or over a wide-area network (WAN), which can cross metropolitan and regional areas all the way to national, international and transoceanic distances. It is a form of optical communication that relies on optical amplifiers, lasers or LEDs and wave division multiplexing (WDM) to transmit large quantities of data, generally across fiber-optic cables. Because it is capable of achieving extremely high bandwidth, it is an enabling technology for today’s Internet and the communication networks that transmit the vast majority of all human and machine-to-machine information.

Optical IP Switching (OIS), is a novel method of creating transparent optical connections between network nodes using a flow-based approach. An IP flow is a collection of IP packets going from the same source to the same destination: the exchange of IP packets is the mechanism that allows the transport of information over the Internet.

Optical add-drop multiplexer

An optical add-drop multiplexer (OADM) is a device used in wavelength-division multiplexing systems for multiplexing and routing different channels of light into or out of a single mode fiber (SMF). This is a type of optical node, which is generally used for the formation and the construction of optical telecommunications networks. "Add" and "drop" here refer to the capability of the device to add one or more new wavelength channels to an existing multi-wavelength WDM signal, and/or to drop (remove) one or more channels, passing those signals to another network path. An OADM may be considered to be a specific type of optical cross-connect.

ITU-T defines an Optical Transport Network (OTN) as a set of Optical Network Elements (ONE) connected by optical fiber links, able to provide functionality of transport, multiplexing, switching, management, supervision and survivability of optical channels carrying client signals. An ONE may Re-time, Re-Amplify, Re-shape (3R) but it does not have to be 3R – it can be purely photonic.

Fiber media converter

A fiber media converter is a simple networking device that makes it possible to connect two dissimilar media types such as twisted pair with fiber optic cabling. They were introduced to the industry in the 1990s, and are important in interconnecting fiber optic cabling-based systems with existing copper-based, structured cabling systems. They are also used in metropolitan area network (MAN) access and data transport services to enterprise customers.

Optical mesh network

An optical mesh network is a type of optical telecommunications network employing wired fiber-optic communication or wireless free-space optical communication in a mesh network architecture.

Admission control is a validation process in communication systems where a check is performed before a connection is established to see if current resources are sufficient for the proposed connection.

Multicast lightpaths

A multicast session requires a "point-to-multipoint" connection from a source node to multiple destination nodes. The source node is known as the root. The destination nodes are known as leaves. In the modern era, it is important to protect multicast connections in an optical mesh network. Recently, multicast applications have gained popularity as they are important to protecting critical sessions against failures such as fiber cuts, hardware faults, and natural disasters.

Dr. Jason P Jue is a Professor of computer science and the director of the Advanced Networks Research Lab at the University of Texas at Dallas.


  1. G. M. Bernstein, Y. Lee, A. Galver, J. Martensson, "Modeling WDM wavelength switching systems for use in GMPLS and automated path computation," IEEE/OSA J. Optical Comm. Netw., vol. 1, no. 1, pp. 187–195, Jun. 2009. doi : 10.1364/JOCN.1.000187
  2. A. Farrel and I. Bryskin, "GMPLS architecture and applications," The Morgan Kaufmann Series in Networking, 2006.