Adaptive registration in TWDM-PON with ONU migrations

In time and wavelength division multiplexed passive optical networks (TWDM-PONs), optical network unit (ONU) migration (equivalently retuning working wavelength pairs) is an effective approach to reducing power consumption at the optical line terminal (OLT) side. Migration delay, the time from when a migration is initiated until the migrating ONU(s) have successfully joined the target wavelength pair, may affect the user service level agreement (SLA) and should be minimized. After an ONU migration process has been triggered, both the ONUs to be migrated (the migrating ONUs) and the newly incoming ones will have to register (referred to as activation in the ITU-T G.984.3 standard) in the upcoming quiet windows. This makes the number of ONUs competing in a single quiet window much more dynamic and leads to unpredictable registration performance and longer registration delay, which in turn will have a negative impact on the migration delay. In this paper, we propose an adaptive registration scheme in a TWDM-PON with ONU migrations. In the proposed scheme, the size of the quiet window is adaptively adjusted according to the up-to-date number of involved ONUs (including both ONUs to be migrated and the newly incoming ones). We show through simulations that the proposed scheme reduces average migration delay and increases the bandwidth utilization, especially when a large number of ONUs are involved in a registration process. In addition, we further investigate the length of the discovery cycle and find a shorter discovery cycle is needed to reduce migration delay and satisfy the requirement of the ONU SLA for a large number of involved ONUs. To realize a 99.999% ONU SLA, the length of the discovery cycle has to be shorter than 0.1 s for 128 involved ONUs and 0.15 s for 32 involved ONUs.