high as $10,000 per lambda and in some cases even more. Up to the present time, DWDM has only been cost-effective for long-haul applications. DWDM technology has been available for over a decade, but the early applications were restricted to providing two or four widely separated wide- band wavelengths. Only in the past five years has the technology evolved to the point where parallel wavelengths can be densely packed and integrated into a transmission system. By conforming to the International Telecom- munications Union (ITU) channel plan (the ITU Grid), such a system ensures interoperability with other equipment. 3.2 SONET Technology Narrowing down from the broader preliminary discussion of optical sys- tems provided in Section 3.1, this section focuses more directly on SONET technology. Traditional SONET Architectures 3.2.1 Overview SONET is a North American specification for optical transport originally formulated by the industry in the mid-1980s and codified in the early 1990s into an American National Standards Institute (ANSI) standard. SONET principles were also incorporated into the SDH recommendations of the ITU, which sets standards for international telecommunications. The basic goals of SONET include the following: Compatibility of equipment between vendors who manufacture to the standard (often referred to as mid-span meet) Synchronous networking Enhanced OAM&P More efficient add/drop multiplexing Standards-based survivable rings/meshes A Layer 1 infrastructure for the transport of new services, such as IP, ATM, and 10 Gigabit Ethernet (10 GbE) wide area network (WAN) SONET defines optical carrier (OC) levels and electrically equivalent Synchronous Transport Signals (STSs) for the fiber-optic-based transmis- sion hierarchy. The most common SONET line rates and STS-equivalent formats are shown in Figure 3-5. Multiplexing is accomplished by combin- ing (or interleaving) multiple lower-order signals (such as 1.5 Mbps, 45 Mbps, and SO on) into higher-speed circuits (such as 51 Mbps, 155 Mbps, and SO on)