Energy efficient multicasting in TDMA PONs

Multicast transmission is utilized in Time Division Multiple Access (TDMA) Passive Optical Networks (PONs) to efficiently and selectively send downstream data to subsets of users. For example, multicast can be exploited in open access PONs to offer various services provided by different providers to the end-users. In this scenario, the minimization of the energy consumption, which is one of the greatest contributors to PON CAPEX, would benefit not only service providers but also end-users. This paper proposes an energy efficient multicasting solution based on energy efficient optical network units (ONUs). Energy savings are achieved by setting to sleep mode the ONUs that need not receive downstream data, i.e. are not subscribed to a multicast group. Sleep mode is combined with an optimal multicast group scheduling to minimize the transitions from sleep to active mode, which consume power for achieving synchronization. Results show that energy efficient multicast transmission reduces the energy consumption with respect to the current broadcast-based transmission. The improvement is more significant when only one user is connected to an ONU (i.e., FTTH) than when several users are connected to the same ONU (i.e., FTTB). This is due to the fact that the higher is the number of subscribers connected to an ONU the higher is the likelihood that an ONU must be active most of the time.