Demanding applications like distributed multi-physics simulations benefit from the combined computational performance and data storage of multiple clusters. A reservation mechanism spanning these clusters ensures the availability of all selected resources. Complex workflows with chronological dependencies are supported. This approach addresses network resources the same way as computation and storage resources. A Meta Scheduling Service (MSS) does the orchestration of resources of different administrative domains, based on an advance reservation capability of local resource management systems. The combined reservation of computational, storage and network resources as done in the VIOLA project for UNICORE based Grid applications, allows a user or application driven selection and reservation of network connections with dedicated QoS based on evolving network technologies. The integrated network management system ARGON is a cornerstone of the next generation Grid enabled optical networks rendering the network to a first class Grid resource.