© 2016 Optical Society of America. In elastic optical networks, the success of providing high network capacity depends on the optical signal-to-noise ratio (OSNR) values of network lightpaths. As each lightpaths OSNR value defines the modulation format and capacity it can support, having high OSNRlightpaths is always beneficial. Hence, with a given set of modulation formats, service providers need to optimize their optical infrastructure, including in-line amplifiers and reconfigurable optical add-drop multiplexers (ROADMs), given the size and topology of their core networks. This also will have a direct impact on vendors who need strong insight into the requirements of service providers and their networks in terms of equipment and new technology. Therefore, in this paper a comprehensive model based on the local optimization which leads to a global network optimization (LOGON) strategy of the Gaussian noise (GN) model has been proposed, which helps in estimating the lightpath OSNR and clearly quantifies the noise contributions from in-line amplifiers and post-amplification at the ROADMs. The model introduces closed-form expressions to calculate nonlinear impairment (NLI) contributions for various span lengths while using either erbium-doped fiber amplifiers (EDFAs) or H-Raman amplifiers, which helps in optimizing the signal launch power to achieve maximum link OSNR. In addition to this, an offline strategy has been proposed that can help service providers to optimize their procurement of network equipment upfront and give insight into how much of the capacity bottleneck is alleviated in their networks if they do this. To demonstrate all of the above, the UK, Pan-European, and US Core networks have been considered, which illustrate differences in link lengths and reduced node density. It is seen that improving the OSNR conditions at the ROADM increases the network capacity when noise from in-line amplifiers is significantly reduced. Among the three networks, we found that the UK network responded the most to improved OSNR conditions at the ROADM nodes due to small link lengths and less line noise. Among the amplifiers, we found that improving ROADMs while having H-Raman in the links resulted in a maximum capacity increase. For the UK network at FG=12.5 GHz, the capacity increases by 6650 Gbps, while for the larger Pan-European and US networks, the capacity increase reduces to 4550 and 1600 Gbps due to increased link lengths and line noise. Further, following the offline strategy, we are able to accommodate 1737, 1481, and 615 100G demands using H-Raman for the UK, Pan-EU, and US networks at FG=12.5 GHz until 10%blocking is reached. Thereby, H-Raman provides 7.5%, 35.8%, and 94.9%extra capacity, respectively, for the UK, Pan-EU, and US. Finally, using H-Raman, all lightpaths in the UK network operate at PM-64QAM with maximum capacity at the end of the procedure.