Optical networks

Optical technologies are today the winning approach for point-to-point transmission in presence of large bandwidth-delay products, i.e., for large high-speed networks. Wavelength Division Multiplexing (WDM) techniques reached maturity so that several high speed transmission channels can be multiplexed on a single physical fiber. Optical technologies can find interesting applications beyond transmission in switching and other network functionalities. The TNG group has been active in the following research areas related to optical networks.

  • Wavelength routing networks offer transparent end-to-end optical channels called lightpaths in a WDM infrastructure based upon optical cross-connects. In this framework we have investigated the Logical Topology Design (LTD) problem, aimed at finding an optimal set of lightpaths given user requests and topology constraints, and the Routing and Wavelength Assignment (RWA) problem, which finds an optimal allocation of a set of lightpaths to the available physical resources and wavelengths. For the LTD problem, the notion of super-lightpath was defined, for which time-division techniques at the source permit to groom several information streams for different destinations in a multi-drop fashion. For the RWA problem, algorithms that takes into account physical-level impairments were proposed and studied. We also studied the design of cross-layer fault recovery schemes, considering IP networks overlayed on WDM wavelength-routed infrastructures and comparing approaches in which link faults are recovered either at the IP layer or at the WDM layer.
  • Design and prototyping of WDM metro networks. A significant experimental effort was devoted to the experimental realization of a WDM packet metro network in the PhotonLab and LIPAR laboratories. We defined an optical packet network architecture, called WONDER, based upon a WDM linear topology (bus or ring) and node interfaces equipped with tunable transmitters and fixed receivers. Fully equipped nodes were built in the labs, capable of transmitting packets generated by standard Internet applications in the WDM network, hence implementing all layers of the protocol architecture. Access control algorithms suited for out architecture were conceived and studied, together with distributed fault-recovery schemes. The node architecture is based on optical components, electro-optical subsystems, and an advanced node controller based upon a high-performance FPGA board.

Design of optical packet switching architectures. Several approaches to exploit optical technologies in packet switching architectures were proposed and investigated. These range from all-optical approaches, in which contention resolution is based upon fiber delay lines, to hybrid electro-optical architectures, in which optics is in charge of packet forwarding, while contention resolution and switch control are performed in the electrical domain. Particular care was devoted to the best blend of optical and electrical technologies for a cost-efficient and scalable switch design. In this framework, a recent activity focused on the analysis of optical switching fabrics, considering physical-layer constraints (such as power losses and noise accumulation), to assess the maximum achievable switching capacity with the technology available today, taking also into account the complexity (in term of cost and number of required optical components), and the power requirements of the different fabric architecture.

Contact person: Bianco Andrea

Research groups