The IEEE 802.11s standard defines a path selection algorithm, named HWMP (Hybrid Wireless Mesh Protocol) which combines on-demand path selection mode with a proactive tree building mode. The proactive tree building mode in HWMP periodically maintains the routing table according to a constant value. Varying this value will affect directly the number of messages transmission, the accuracy of the routing table and delays for path recovery. Frequent messages transmission will cause high overhead but improves the accuracy of the routing table. On the other hand, big tree updates intervals may cause long delays for path recovery in case of a broken link. In this paper we propose a performance evaluation of the HWMP proactive tree mode. Indeed, we vary the periods of messages transmitted for two different topologies of Wireless Mesh Network (WMN) functioning as a backbone based on IEEE 802.11s standard and generating the same traffic. By consequent we expect improving QoS requirement.