A network apparatus of a cellular network for synchronizing at least one user equipment (UE) for a sidelink, comprising a processor adapted to receive from a first UE which is connected to the cellular network a request to establish a sidelink with at least a second UE, receive from the first UE a connectivity state information, in particular on channel quality, connectivity and/or timing, of the first UE and/or of at least the second UE and instruct the first UE to establish or decline the sidelink after synchronizing according to an action selected by the network apparatus from a plurality of action based on at least one of: the connectivity state and at least one operational condition of the cellular network.