The VIS architecture makes use of centralised services, which are accessible from the different Member States. For resiliency purposes these centralised services are duplicated to two different locations namely Strasbourg, France, hosting the principal CS-VIS, central unit (CU) and St Johann im Pongau, Austria, hosting the backup CS-VIS, backup central unit (BCU) in accordance with Commission Decision 2006/752/EC of 3 November 2006 establishing the sites for the Visa Information System during the development phasenote.