In this paper, we propose a framework to study how to effectively perform loadsharing in multipath communication networks. A generalized load sharing (GLS) model has been developed to conceptualize how traffic is split ideally on a set of active paths. A simple traffic splitting algorithm, called packet-by-packet weighted fair routing (PWFR), has been developed to approximate GLS with the given routing weight vector by transmitting each packet as a whole. We have developed some performance bounds for PWFR and found that PWFR is a deterministically fair traffic splitting algorithm. This attractive property is useful in the provision of service with guaranteed performance when multiple paths can be used simultaneously to transmit packets whic...