Section: New Results

Algorithms: Bandwidth Allocation in Optical Networks

Participants : Christine Fricker, Philippe Robert, James Roberts.

The development of dynamic optical switching is widely recognized as an essential requirement to meet anticipated growth in Internet traffic. Since September 2009, RAP has begun an investigation into the traffic management and performance evaluation issues that are particular to this technology. A first analysis of passive optical networks used for high speed Internet access has led to the proposal of an original dynamic bandwidth allocation algorithm and to an evaluation of its traffic capacity. Our activity on optical networking is carried out in collaboration with Orange Labs with whom we have had a research contract and are currently finalizing a new one. We have also established contacts with Alcatel-Lucent Bell Labs and had fruitful exchanges with Iraj Saniee and his team on their proposed time-domain wavelength interleaved networking architecture (TWIN).

We have also analyzed the traffic capacity of wavelength division multiplexing (WDM), passive optical networks (PONs) where user stations (optical network units) are equipped with tunable transmitters. For these systems users can use any of the multiple wavelengths to transmit their data but only within the limit determined by the number of transmitters they possess. A mean field approximation is investigated to estimate the capacity of a limited-gated multiserver polling system with a limit on the number of servers a given station can use simultaneously. The approximation provides an expression for the stability limit under very general assumptions about the traffic process and system configuration.

More generally, motivated by these next generation passive optical networks, a multi-server polling system has been studied where the number of servers that can attend to a queue simultaneously is limited. The stability condition is investigated for this model under quite general assumptions. The result is proved for unlimited service policies. The paper [1] presents a conjecture for the case of limited service policies and general service limits. A simulation study shows that the stability conditions may hold.

In 2011, we have worked on bandwidth allocation in meshed networks. A first study applies the TWIN architecture for a metropolitan area network but with an original medium access control (MAC) algorithm. This algorithm is inspired by our prior work on access networks and ensures an efficient and fair allocation of bandwidth to flows between network nodes. The paper [9] describes this network architecture and presents a performance evaluation using analytical models backed up by simulations.

The TWIN architecture is not extensible to a wide area for reasons of scalability and the excessive signalling delay between geographically distant nodes. We have therefore invented a new notion of a multipoint-to-multipoint lightpath that avoids these problems. A patent application relating to this invention has been submitted. This patent is owned by Orange following the terms of our contract with them. The second patent (that simply perfects the first invention) is jointly owned since the research was performed after the end of this contract. The submitted paper [13] describes the invention and its evaluation. A major advantage demonstrated in this paper is the energy saving achieved by the use of the proposed optical technology in place of electronic routers.

Ongoing research seeks to apply this type of networking solution to data centres, on one hand, and to geographically spread tier 1 Internet carrier networks, on the other. This work is performed in collaboration with Orange Labs and will be covered by a contract that is close to being finalized. We have also participated in the preparation of a European CELTIC project proposal that includes a work package dedicated to the development and experimentation of the network proposed in [13] .