Passive optical networks are dominating access networksaround the world due to its their economical aspect, bandwidth, and penetration. It is necessary to deal with specification of these networks. The article deals with a transmission convergence layer of a Gigabit passive optical network, especially the activation process for ONUs. When the blackout affects all ONUs in the network, all ONUs need to be resynchronized with OLT but the current algorithm affects that for higher value of ONUs synchronization after a couple of minutes. We proposed a novel algorithm for an ONU activation time with the same frame structure and state machine, which are defined in the main specification. We verified the proposed algorithm by simulation and compare results for the current and novel algorithms. Ourresults confirm that it is possible to achieve the better time up to nineteen times lower synchronization time in comparison with the current algorithm.