Optimal multi-period provisioning of fixed and flex-rate modular line interfaces in DWDM networks

Flex-rate transmission is seen as a core element in the realization of programmable backbone networks. The ability to adjust the channel bit rate in response to traffic changes in the network can potentially bring long-term savings by future-proofing capacity and simplifying network operations. The key issue in this topic is quantifying the degree of traffic dynamics and growth that justify the higher initial investment in flexible-rate (flex-rate) technology. In dense wavelength division multiplexing (DWDM) networks, traditionally featuring long lifespans and stable traffic growth outlooks, this question can be answered with a multi-period analysis that simulates the requirements for hardware provisioning throughout multiple planning periods with incremental traffic. In a scenario featuring sliceable bandwidth-variable transponders composed of line cards (LCs) with multiple transceiver ports, we use a multi-period planning framework to assess the advantages and drawbacks of using fixed-rate and/or flex-rate technology in the LCs and transceivers. The simulation is performed resorting to an integer linear programming (ILP) model that chooses, in each period, the routing and format selection for a set of demands that yields the minimum hardware cost, reusing any idle equipment resulting from traffic churn. The analysis of the results shows that the initial investment in flex-rate LCs and transceivers pays off for small- to medium-sized networks where the upgrade to higher bit rates does not require extra regeneration. Long and ultralong-haul scenarios benefit from the use of fixed-rate interfaces. In terms of operational issues, it is shown that flex-rate hardware provides clear benefits through reduced footprint and extended capacity due to better spectral efficiency.