A computational grid is a accumulation of geographically dispersed computing resources, providing a large virtual computing system to users. Prerequisite resources is one of the prominent Challenges. Federated Environment such as InterGrid, facilitate sharing, selection, and aggregation of resources across several Grids, which are connected through high bandwidth network connections. Due to the immense Virtual Machine’s availability , the protocol of lease abstraction came as emerging. Two segregated users are present 1. Local Users 2. External Users. Local users (local requests), refer to users who ask their local cluster resource manager (LRM) for resources. External users (external requests) are those users who send their requests to a gateway (IGG) to get access to a larger amount of shared resources. While giving priority to external request, local request tends to wait. Serving local users can be solved by preempting VMs from external users which impose overheads on the system. The challenge is reducing VM Preemption with more QOS. An analytical queuing model is proposed, based on the routing in parallel non-observable queues. Deterministic Dispatch Policy to prioritize user is also proposed. Simulation request implies that VM preemtion is decreased by 60%. Simple greedy scheduling scheme was proposed Preempting VMs imposes a notable overhead to the underlying system and degrades resource utilization. On concentrating from the external user perspective, preemption increases as the response time of the external requests.