ONU Migration And Registration Mechanism In TWDM-PON

Time and Wavelength Division Multiplexed Passive Optical Network(TWDM-PON) is considered to be one promising candidate of next generation Passive Optical Networks stage2(NG-PON2),because it can combine the flexibility of Time Division Multiplexed Access Passive Optical Network(TDMA-PON) with the increased overall capacity of Wavelength Division Multiplexed(WDM) technology. Due to the uneven distribution of online ONUs at different time in a day, the wavelength utilization is often low in a TWDM-PON. An Optical Network Units(ONU) migration mechanism within TWDM-PON has been proposed,in which ONU(s) can be migrated to a smaller number of active wavelength pairs, and the rest ones are powered off to save energy. During the migration process, the migrating ONUs firstly de-register from current wavelength and register at the target wavelength, which needs undergoing a migration delay. Migration delay refers to the time from when a migration is triggered until the migrating ONU(s) has successfully joined the target wavelengths, which may affect the user service level agreement(SLA) and should be minimized. After an ONU migration process has been initiated, both the newly incoming ONUs and the migrating ones will register in the upcoming quiet windows. This makes the number of ONUs registering in a quiet window much more dynamic and results in unpredictable and longer registration delay, which will have a negative effect on the migration delay.In this paper, we first redesign registration protocols and message in ONU migration mechanism according to G984.3 standard. Moreover, we investigate the registration process and registration efficiency and find the relationship between the optimal quiet window size and the number of involved ONUs to maximize the registration efficiency. Finally, an adaptive registration scheme in TWDM-PON with ONU migrations is proposed, in which the quiet window size is adaptively adjusted with the number of involved ONUs. From simulation results,we conclude that the proposed scheme increases the bandwidth utilization and reduces average migration delay, especially when the number of involved ONUs in a quiet window is large. In addition, we further investigate the length of discovery cycle, and show through simulations that shorter discovery cycle can reduce migration delay. To meet 99.999% ONU SLA, the length of discovery cycle should be shorter than 100 ms for 128 involved ONUs and 150 ms for 32 involved ONUs.