Summary form only given. The current expansion of communication networks offer services for private individuals in terms of access to information, communication between individuals, interactive play, as well as for economic or technical purposes such as banking applications, air traffic control, telerobotics, remote maintenance, medicine, etc. Data sent are converted into segments subjected to network constraints, namely delays, erroneous arrivals of messages or even loss of messages. With taking these constraints into consideration, our contribution is focused on network modeling, study of network dynamic behavior and of congestion avoidance. It is possible with this network modeling to determine the influence of communication networks on the transmission of control signals, since there are delays and losses induced by networks. This paper presents the modeling of a communication line in Internet environment under TCP/IP protocol. The behavior of the communication line is modeled as a continuous system (message flows); it is a satisfactory approximation. The behavior of the TCP protocols is seen as a discrete event system model. In this case, the global model is hybrid. We have chosen hybrid PNs as a unique modeling tool, since it gives accurate models of the complex functions found in Internet connections.