If a custodial sentence is to be served, the enforcement of the sentence shall be ordered by the sentencing court and the competent correctional institution shall be notified of the order.
If the convicted person is not already in custody and does not begin the sentence immediately, he shall be summoned in writing to begin the sentence within three months of the service of the summons. This summons shall also contain the threat that he will be brought before the court in the event of non-compliance.
If the convicted person is already in custody, he shall be transferred to the penitentiary, provided that he is in the competent institution for the execution of custodial sentences. If he is in another institution, he shall be transferred to the competent prison.