DWDM Tutorial

SONET and DWDM: Competing Yet Yet Complementar Complementary y Technolo Technologies gies for The Metro Network 

Introduction  The next generation of SONET equipment has been well accepted by service providers and is being usefully deployed into networks today to carry continually increasing network traffic. Compared to traditional SONET equipment, NGADM is characterized by simple architecture, scalability, high capacity add/drop, multiple ring terminations, multiservices, and multiple fabrics, including STS and VT switching capabilities. At the same time, DWDM equipment is increasingly showing its viability in today’s metro networks with tremendous available bandwidth over the existing fiber plant, along with a variety of service interfaces and superior optical transmission capabilities. A new generation of equipment is also being rolled out that provides features of both SONET and DWDM. Some are DWDM systems with integrated SONET units that provide grooming, add/drop and protection of a wavelength. Others are NGADMs with built in DWDM capability that provide optical multiplexing, amplification and transmission. Although a higher capacity technology such as DWDM brings about many benefits, this technology can also incur higher initial cost. In quite a few situations, we need to evaluate the benefits gained from DWDM and SONET against the economical impact that each inherits. Important questions that need to be reviewed for each type of system include: why is DWDM needed; when is it needed; under what circumstances is DWDM more economical than a SONET architecture; what are the factors that need to be taken into account for the deployment of DWDM technology; and when is SONET grooming beneficial?

The Scenarios of the Study  This paper investigates an example metro network from some real life IOF applications to answer some of  the questions previously mentioned. In this example network, three network architectures are discussed (see Figure 1): • PMO – a SONET ring architecture with cross-connects and local rings • SONET Overlay – a SONET ring architecture that uses optimized overlaid rings to avoid ports at the pass-through nodes in the network  • DWDM – an architecture in which DWDM equipment is deployed for transport with SONET aggregation as needed for each wavelength  The main objective of this study is to investigate the crossover points at which the economical advantages of the SONET approaches and the DWDM approach exchange positions.The factors that directly influence the crossover point in question are the network traffic volume, distances between sites in the network, circuit types (OC-3, OC-12, OC-48 or Gigabit Ethernet), density of interface cards and shelf itself, diversity of  traffic and the equipment cost. We will also discuss other impacts on selecting a core SONET versus a core DWDM architecture in a carrier’s metro network.

FUJITSU NETWORK COMMUNICATIONS INC. 2801 Telecom Parkway, Richardson, Texas 75082-3515 Telephone: (972) 690-6000 (800) 777-FAST (U.S.) us.fujitsu.com/telecom

For your convenience, a list of acronyms can be found at the end of this document.

1