To support service guarantees in packet-switched networks, three approaches have been proposed. They are the Stateless Core (SCORE) approach, the Integrated Services (IntServ) approach, and the Differentiated Services (DiffServ) approach. The granularities of service guarantees provided by these approaches at each router are respectively packet level, flow level, and class level. In this paper, we propose a novel approach, called Link-Based Fair Aggregation (LBFA) approach to scalable support of service guarantees. While the granularity of service guarantees supported by LBFA is link level at each router, we show through analysis that the proposed LBFA approach can achieve as good as or even better per-flow service guarantees than the current three approaches.