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Besides being very application specific the design and performance evaluation of wireless sensor networks (WSN) is also very dependent on another inherent feature of these networks - the mobility of the sensor nodes. A major challenge is to provide reliable and energy-efficient operation taking into consideration different mobility models. On the other hand, due to the multi-hop nature of many WSN local contention can lead to network-wide congestion and reduce both the efficiency and the lifetime of the network. In this paper we study the interdependence between end-to-end congestion and local contention taking into consideration different mobility scenarios. The work is based on the slotted CSMA/CA medium access control method adopted in IEEE 802.15.4 protocol specification for LR-WPAN and covers beacon-enabled mode. Random waypoint mobility model (RWP) and ad hoc on demand (AODV) routing protocol are used. Beacon-enabled mode is chosen because it includes regulating the activity period of each single node. The aim is to investigate the effects of changing local contention regulating parameters (activity periods, number of MAC layer retransmissions and transmission buffer size) on the overall network congestion in different mobility scenarios.