ABSTRACT
An ongoing effort is being made to improve the span of performance of optical transport networks that comprise traditional synchronous optical network (SONET)-based and recent high-capacity dense wavelength division multiplexing (DWDM) systems installed to increase the available bandwidth and reduce overall costs. Although extending the geographic reach of optical-transport equipment is an essential part of any cost-cutting strategy, it does not address some of the greatest cost factors in the network operations, such as those associated with optical cross-connects (OXCs) 1 and switching. 2
In the “traditional” network architecture, with its back-to-back DWDM terminals and an OXC in between, one relies on the OXC to:
1. Speed up service delivery by routing the wavelengths involved in both dynamic and semi-permanent connections
2. Perform mesh-restoration functions; however, some architectures assign various other tasks to the OXC for which it is not well suited, leading to higher capital/operating costs
For example, when both the dynamic reconfiguration of all-optical trunks or “lightpaths,” as well as mesh restoration is required, the OXC has a serious limitation in that it cannot scale readily to thousands of ports. Therefore, it hinders the equipment’s ability to provide a broad range of new, dynamically provisioned services across the user base. It also creates “islands” of dynamically configured lightpaths with manual patching to connect between them in the optical transport networks landscape. In addition, the continuing growth of data applications in today’s Internet-driven economy means that a significant portion of the communications traffic traversing the multi-node networks is express or pass-through traffic, especially at smaller, two-way junctions. The ideal solution is an alternative to the OXC-a more cost-effective way to create and manage the semi-permanent connections to handle this type of traffic. In the following sections,
we review some selected aspects of optical transport networks pertinent to the contemporary architecture and future proliferation.
