Methodology & Benchmarking. One fundamental hypothesis of SODALES is that actively switched network architectures are more energy-efficient than the traditional passive optical networks (PON). In the traditional PON shown in Figure 32 left, the traffic of many users is aggregated in a passive optical node (being essentially a fibre coupler) and then amplified by an erbium-doped optical fibre amplifier (EDFA) or semiconductor optical amplifier (SOA) for reducing the splitting loss, scaling like 10 log10 N, which can be huge for large numbers users N. Statistical multiplexing, which is sometimes also denoted as over-provisioning, is performed at the second aggregation level by using time-division, orthogonal frequency-division or wavelength- division multiple access (TDMA, OFDMA and WDMA, respectively). Main efforts regarding energy consumption are found in the electric-to-optic conversions at the CPE and at second aggregation levels. Moreover, potentially needed optical amplifiers and the processing of the multiple access protocol by means of TDMA or OFDMA cost significant energy. WDM has a clear advantage in terms of energy efficiency, since optical wavelength are passively combined or split in the AWG. However, the high costs of AWGs increase the CAPEX at the cost of a reduced OPEX. a EDFA/ SOA p a a Figure 32: Left: Traditional PON architecture. Right: In an actively switched architecture, the passive node and amplifier is replaced by an ARN in the first aggregation step which is also responsible for the statistical multiplexing. In the SODALES architecture, the passive node and the (potentially needed) amplifier are replaced by an active remote note (ARN) to which each user is directly connected. From an information-theoretic point of view, this is a two-hop link using decode-and-forward plus statistical multiplexing at the ARN. Since path lengths are shorter, owing to exponential attenuation versus distance, in principal two short hops are more energy efficient than a long one. This effect is relevant in wireless networks, while in optical links it has the consequence that the SNR per user is increased, enabling a higher throughput per user, i.e. the same data can be delivered in a shorter time. The two-hop architecture considered in SODALES offers space for both, increasing the user data rates and reducing the energy consumption.
