An approach to traffic engineering that uses differentiated services (DS) and multi-protocol label switching (MPLS) to provide quantitative network quality of service (QoS) guarantees over an IP network was proposed. The traffic associated with assured forwarding (AF) Per-Hop behavior (PHB) in differentiated services enabled IP network was modeled. Furthermore, the effect of such traffic on network resources with the objective of developing efficient traffic engineering methodologies was analyzed and the optimization problem relating to traffic engineering in DS networks with an MPLS core was formulated. The service 收稿日期:by TCP and UDP flows when they share either a link or a MPLS traffic trunk was also compared and found that in order to benefit from traffic engineering, MPLS trunks should be implemented end-end (first router to last router). If some part of the network is MPLS trunk-unaware, the benefits are reduced or eliminated.