Dense Wavelength Division Multiplexing

Abstract

This paper deals with the twin concepts of optical networking and dense wavelength division multiplexing. The paper talks about the various optical network architectures and the various components of an all-optical network like Optical Amplifiers, Optical Add/Drop Multiplexers, Optical Splitters etc

. Important optical networking concepts like wavelength routing and wavelength conversion are explained in detail. Finally this paper deals with industry related issues like the gap between research and the industry, current and projected market for optical networking & DWDM equipment and future direction of research in this field.

INTRODUCTION

One of the major issues in the networking industry today is tremendous demand for more and more bandwidth. Before the introduction of optical networks, the reduced availability of fibers became a big problem for the network providers. However, with the development of optical networks and the use of Dense Wavelength Division Multiplexing (DWDM) technology, a new and probably, a very crucial milestone is being reached in network evolution. The existing SONET/SDH network architecture is best suited for voice traffic rather than today's high-speed data traffic. To upgrade the system to handle this kind of traffic is very expensive and hence the need for the development of an intelligent all-optical network. Such a network will bring intelligence and scalability to the optical domain by combining the intelligence and functional capability of SONET/SDH, the tremendous bandwidth of DWDM and innovative networking software to spawn a variety of optical transport, switching and management related products.

Optical Networking

Optical networks are high-capacity telecommunications networks based on optical technologies and component that provide routing, grooming, and restoration at the wavelength level as well as wavelength-based services. The origin of optical networks is linked to Wavelength Division Multiplexing (WDM) which arose to provide additional capacity on existing fibers. The optical layer, whose standards are being developed, will ideally be transparent to the SONET layer, providing restoration, performance monitoring, and provisioning of individual wavelengths instead of electrical SONET signals. So in essence a lot of network elements will be eliminated and there will be a reduction of electrical equipment.
It is possible to classify networks into three generations depending on the physical-level technology employed. First generation networks use copper-based or microwave technologies e.g Ethernet, satellites etc. In second generation networks, these copper links or microwave links with optical fibers. However, these networks still perform the switching of data in the electronic domain though the transmission of data is done in the optical domain. Finally we have the third generation networks that employ Wavelength Division Multiplexing technology. They do both the transmission and the switching of data in the optical domain. This has resulted in the onset of tremendous amount of bandwidth availability. Further the use of non-overlapping channels allows each channel to operate at peak speeds.

1.2 Dense Wavelength Division Multiplexing (DWDM)

Dense Wavelength Division Multiplexing (DWDM) is a fiber-optic transmission technique. It involves the process of multiplexing many different wavelength signals onto a single fiber. So each fiber has a set of parallel optical channels each using slightly different light wavelengths. It employs light wavelengths to transmit data parallel-by-bit or serial-by-character. DWDM is a very crucial component of optical networks that will allow the transmission of data: voice, video-IP, ATM and SONET/SDH respectively, over the optical layer.
Hence with the development of WDM technology, optical layer provides the only means for carriers to integrate the diverse technologies of their existing networks into one physical infrastructure.
For example, though a carrier might be operating both ATM and SONET networks, with the use of DWDM it is not necessary for the ATM signal to be multiplexed up to the SONET rate to be carried on the DWDM network. Hence carriers can quickly introduce ATM or IP without having to deploy an overlay network for multiplexing.