Section: New Results

Optical Networks

Participants: Nicolás Jara, Gerardo Rubino

The rapid increase in demand for bandwidth in communication networks has caused a growth in the use of technologies based on WDM optical infrastructures. Nevertheless, in this last decade many researchers have recognized a “Capacity Crunch” associated with this technology, a transmission capacity limit on optical fibers, that is close to be reached pretty soon. This situation claims for an evolution on the currently used WDM optical architectures, in order to satisfy this relentless exponential growth in bandwidth demand. Following this trend, research started to examine in some detail specific aspects of the present functioning, and in particular, the way these networks are operated. Currently, optical networks are operated statically, but this is known to be inefficient in the usage of network resources, and with the previously mentioned upcoming risk of capacity collapse, it is of pressing matter to upgrade it. To this purpose, several proposals have been addressed and researched so far. Among these solutions, dynamic optical networks is the one closest to be implemented, but it has not been considered yet since the network cost savings are not enough to convince enterprises. This has been the focus of our research effort in the area.

The design of dynamic optical networks decomposes into different tasks, where the engineers must basically organize the way the main system's resources are used, minimizing the design and operation costs and respecting critical performance constraints. These tasks must guarantee certain level of quality of service (QoS) pre-established in the Service Level Agreement. In order to provide a proper quality of service measurement, we propose a new fast and accurate analytical method to evaluate the blocking probability that is at the heart of the path toward solving all the mentioned design problems. Blocking probability is the main QoS metric considered in the field. This work has been done in [20], where an analytical procedure has been proposed that combines efficiency and accuracy.

Next, the different tasks that must be addressed to find a good global design have been addressed in [19]. These are: which wavelength is going to be used by each user (the Wavelength Assignment Problem), how many wavelengths will be needed on each network link (the Wavelength Dimensioning Problem), and which set of paths enabling each network user to transmit (known as the Routing Problem) are to be established in order to minimize costs and to deal with link failures when the network is operating (this is the Fault Tolerance Problem). Two types of innovations and presented in this last paper. First, each of the problems receives a solution shown to be highly efficient. Second, and this is also new, we solve all the design problems simultaneously, using a single global algorithm (the usual way is to isolate them and to solve them one at a time, in a specific order). This work may provide a strategy to finally achieve sufficient cost savings, and thus, to contribute to make the decision to migrate from static to dynamic resource allocation easier. A preliminary version of a part of these results was presented previously in [44].