The general size of ACK packets which are essential components for reliable communications is relatively small in comparison with that of data packets. However, transmissions of ACK packets and data packets require the same amount of communication resource in terms of MAC, and the increase in the number of ACK packets reduces opportunities for the transmissions of data packets. Therefore, delayed ACK was proposed to reduce the number of ACK packets, and the receiver can send fewer ACK packets to the sender by using delayed ACK. On the contrary, in terms of transport layer, ACK packets have an important role of not only the notification of data reception but also increasing the size of sender's congestion window. Thus, the decrease in the number of ACK packets may be a serious impediment to the fast increase in the sender's congestion window. Consequently, a comprehensive cross-layer approach is essential to analyze the effect of delayed ACK in IEEE 802.11. In this paper, we conduct the modeling and the analysis on delayed ACK using the cross-layer approach and verify the modeling and the analysis through simulations. Based on the result of them, we present the direction for decision of optimal delayed ACK maximum count to maximize the performance of communications and network.