Optical Network Services in Future Broadband Networks

Introduction

An optical network is a network where the user-network interface is optical and the data does not undergo optical-to-electrical conversion within the network as it is routed to its destinations. Here, we discuss

• Different optical network architectures according to the services they provide,
• The technologies used to implement those services,
• The geographical size of the network.

There is a great interest in optical network applications in the wide and metropolitan areas. The reasons are that fiber optic transmission technology is progressing faster than electronic switching technology and because optical switching technology is maturing to the point where it may be the economic choice in certain situations. Optical transmission systems supporting 40 Gb/s are commercially available, 100 Gb/s products have been announced, and terabit-per-second systems have been demonstrated in the laboratory. All these are single-fiber systems, while fiber links in metropolitan area networks (MANs) and wide area networks (WANs) are typically composed of fiber bundles with tens of fibers per bundle. Optical networks offer the potential to economically tap this large capacity.

Invention of the 1st laser

Theoretically, optical networks could provide almost any service offered by an electronic network:

• Circuit services,
• Virtual circuit services,
• Datagram services.

However, due to limited technology in optical logic, buffering, and gating, the most practical technology at this time allows only high-bandwidth circuit services. This technology, known as wavelength division multiplexing (WDM) with wavelength routing, or so called OTN, is a major focus of this chapter; however, other network services are possible and nearing practicality.

There are many potential roles that an optical network in a broad-band architecture can play. An underlying principle in thinking about these roles is that in most situations, there is a large mismatch between the services which can practically be offered by optical networks and those desired by end users. Therefore, in almost all situations electronic networks must be overlaid on top of the optical network.

Although optics and electronics can provide similar services, there are major differences between what can practically be offered by each technology. For instance, both SDH and WDM can provide circuits; however, SDH more easily allows the insertion and removal of data within the circuit than WDM. There are therefore significant trade-offs between which services are offered at the optical layer and which by electronics. The resolution of those trade-offs depend heavily on the geographical extent of the network because of different physical layer, topology, and protocol issues as well as different traffic requirements.

The organization of this chapter is as follows. We first discuss broadband network architectures and where optics might play a role in the protocol stack. We then discuss the services optical networks can deliver, the technologies used to implement those services, and some of the major technological limitations. Finally, we use this knowledge base to analyze the potential role of optics in WANs, MANs, and then local area networks (LANs).