Current Quality of Service models such as those embodied in the Differentiated Services proposal, rely on data path aggregation to achieve scalability. Data path aggregation bundles into a single aggregate multiple flows with the same quality requirements, hence decreasing the amount of state to be kept. A similar scalability concern exists on the control path, where the state required to account for individual reservations needs to be minimized. There have been several proposals aimed at control path aggregation, and the goal of this paper is to expand on these works in an attempt to gain a better understanding of the various parameters that influence the efficiency of different approaches. In particular, we focus on inter-domain control aggregation, and compare an Autonomous System (AS) sink-tree based approach with two examples of a shared AS segment based approach, in terms of the amount of state kept, both per AS and per edge router. Our main contributions are in providing a greater understanding into the design of efficient control path aggregation methods.