Differentiated Service (DiffServ) in combination with Multi-Protocol Label Switching (MPLS) is a promising technology in converting the best-effort Internet into a QoS-capable network. This paper describes the design and implementation of key DiffServ components, including classifier, meter/shaper, queue manager, and scheduler, in an MPLS edge router architecture on a network-processor platform. We describe how the DiffServ functionalities were realized and also analyze the performance of the system under different traffic patterns. Various factors that cause performance degradation in the architecture are observed and analyzed. These include receiving processing architecture, transmitting processing architecture, micro-engine processing power, memory access latency, and complexity of each DiffServ component. Among them, we found that traffic classification demands more processing resource and hence is a major factor in limiting the system throughput.