Voice over Internet Protocol (VoIP) is a transmission technology that allows voice to be delivered over the Internet with support of Internet Protocol. Recently, the integration of VoIP and Wireless Local Area Network (WLAN) has become popular, driven by mobility requirements of the users. However, WLAN architecture was primarily designed to carry data and not for voice. Hence, there is a need to enhance the quality of voice transmission over the WLAN. Several metrics such as delay, jitter, and packet lost have impact on the quality of service (QoS) of the VoIP system. Minimizing total transmission delay, jitter and packet lost would mean improving the QoS of VoIP. In this paper, a cross-layer interaction approach is proposed to improve the quality of voice delivery, hence the QoS of VoIP. The approach in achieving this is by introducing a communication agent between Data Link layer and Transport layer, by which congestion misinterpretation by the Transport layer could now be eliminated. In particular, the IP protocol of Transport layer will be utilized to communicate with the agent to improve the QoS of the VoIP system. © 2010 IEEE.