Abstract
AX.25 protocol belongs to the HDLC protocols family and is used, among others, as a data link layer in an amateur Packet Radio network. The paper presents a simple analytical model developed on the basis of protocol frame exchange rules. Then, we compare analytical results to the experimental ones achieved using various different types of TNC controllers that act as network interfaces for Packet Radio network. In the experimental part we focus on both hardware and software properties of TNC that have influence on the effective throughput of the network.