Nonlinear dynamic behaviour of transmission control protocol (TCP) in universal mobile telecommunications system (UMTS) networks is proposed. The dynamic characteristics of TCP are explored using the fundamentals of chaos theory, and the occurrence of chaotic behaviour in relation to the feedback that is received (packet drops, packet delays) by TCP from the network is explained theoritically. To validate the concept proposed, a model of the UMTS network is built and simulated under various user traffic loads. Using standard chaos methodology, it was found that inside the UMTS the TCP exhibits aperiodicity and sensitivity to initial conditions that are inherent characteristics of chaos. In particular, simulation results illustrate that as the traffic load increases, the behaviour of the network ranges from periodically stable to chaotic, with a direct impact on the quality of service of the network.