The vision-an all-optical network

Looking at the evolution of communication networks and standards, they seem to become more and more complex (and hence less manageable-as human beings!) as time goes by. This trend is due in part to the increase in their sizes and bit rates, but mainly to the diversity of the traffic they carry and services they support.

Figure 1 - An all-optical network

The vision of WDM optical networks offers a change in this course of evolution into much simpler network architectures. Their transparency, abundance in resources, and passive nature may eliminate the need for sophisticated mechanisms to optimize the utilization, control, and management of integrated networks. The architectural simplicity is achieved through traffic segregation as opposed to the current trend of traffic aggregation (Fig. 2).

Figure 2 - Optical layers and digital clients

All that remains is to concentrate on the endpoints, namely, how to design computers that can make use of so much bandwidth. Even more important, what new applications are now enabled by these bit rates?

In the futuristic scenario depicted in Fig. 1, wherein the fiber infrastructure is extended to the home (Fig. 3), and in which we can make efficient use of the thousands of wavelengths that theoretically may be multiplexed into a single fiber. Then the global network would be made of fibers interconnected by optical cross-connects, with optical multiplexers at the endpoints. This entire network may be viewed as a huge, sophisticated piece of glass, almost passive in terms of electrical power. When end user X wishes to communicate with end user Y, X requests the network control entity to establish the connection. The network then assigns a wavelength to this connection, sets the switches along the path to support it, and informs both X and Y of the existence of this new connection. Here ends the role of the network in the connection, as opposed to conventional networks in which the network takes an active part in the transfer of the data. Now, when user X sends a light encoded signal on wavelength, it is optically routed from X to Y, received optically at Y, and converted to the electrical domain, to be processed by Y's application. The endpoints of the connection now have an ultra-high-speed, low-noise pipe between them, equivalent to a private fiber that serves them exclusively. The network, acting as a passive piece of glass, is sensitive neither to the protocol that X and Y choose to use nor to the bit rate. It may even be insensitive to the nature of the data (digital or some analog signal). As a result, there need only be a handful of simple protocols of which the network will be aware (and thus will have to be standardized). The rest is up to the users.

Figure 3 – OTN physical topology.

Contrast this scenario with the complexity and extensive monitoring and management required by "traditional" networks, with SDH setting the current record, probably to be eclipsed by broadband integrated services digital network (B-ISDN)/ATM. It is enough to see how much standardization effort is put into other alternatives as such IP and MPLS for high-bandwidth integrated networks to realize the promise that optical networks provide.

As is always the case with vision, reality tells a different story, which we outline in the rest.