Grid computing systems are emerging as a computing infrastructure that will enable the use of wide-area network computing systems for a variety of challenging applications. One of these is the ever increasing demand for multimedia from users engaging in a wide range of activities such as scientific research, education, commerce, and entertainment. To provide an adequate level of service to multimedia applications, it is often necessary to simultaneously allocate resources including predetermined capacities from interconnecting networks to the applications. The simultaneous allocation of resources is often referred to as co-allocation in the Grid literature. In this paper, we formally define the co-allocation problem and propose a novel scheme called synchronous queuing (SQ) for implementing co-allocation with quality of service (QoS) assurances in Grids. Unlike existing approaches, SQ does not require advance reservation capabilities at the resources. This enables an SQ-based approach ...