Power-aware rationale for using coarse-grained transponders in IP-over-WDM networks

Power consumption is becoming one of the most significant limitations while seeking new solutions to cope with the traffic demand increase. 100 Gbps optical transmission technology has the potential to accommodate upcoming traffic demands with improved figures for W/Gbps compared to previous generations. However, the adoption of such coarse-grained bit-rate granularity with lower flexibility for traffic grooming raises important questions: (1) What repercussions do they have on the overall power consumption and thus operational expenditures (OPEX) compared to legacy fine-grained designs (i.e., using 10 Gbps technology)? (2) What is the long-term cost of coarse-grained designs? We define a power-aware mixed integer linear programming (MILP) formulation based on actual modular architectures where modules are upgraded as the network traffic increases. We introduce, for the first time, important practical constraints which were neglected by previous works, so that there is correspondence between interface modules and transponders instead of assuming a single type of interface module per line card, and we use accurate power consumption values instead of using approximations per port. We also present a comprehensive analysis on the trade-off between power consumption and available optical capacity, and power consumption and capital expenditure (CAPEX) for three different scenarios, defining the impact of provisioning the network with higher granularity transmission technology. Regarding the available optical capacity versus power consumption, 37.7% additional optical network capacity is achieved when using exclusively 100 Gbps technology at 13.3%–32.4% power consumption expenses and 15.3% optical network capacity at only a 2.6%–8.8% power consumption penalty when using 40 and 100 Gbps technologies. From a CAPEX perspective, up to 19.4% savings can be achieved by provisioning ahead using coarse-grained designs.