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Basic node-to-node protocol of a packet-switched network based on the multiplexing of the link into logical channels is first described. The node structure is then described based on a set of queues, an input routine, a main-task routine, and an output routine. Three protocols which are based on different implementations of the transmission of the acknowledgment (ACK) block are then introduced. The first one is the 1972 version of the Advanced Research Projects Agency Network (ARPANET), the second places the ACK block in regular packets, and the third uses only control packets. The simulation program developed to compare these protocols is then described. It studies the behavior of a link between two nodes, which consists of a full-duplex line and of two sets of queues. The rest of the packet-switched network is simulated by a packet generator which feeds the two sides of the link. First, comparison of protocols is done using symmetrical and asymmetrical loading conditions. In this last case, interesting results are obtained in relation to momentary saturation of the logical channels. The influence of the limitation of buffers allocated to an output line is also discussed. Sensitivity of protocols to reverse traffic characteristics is then studied and, based on the results, choice of a protocol is discussed. Based on the dynamic behavior of the queue, some questions are raised in connection with adaptive-routing algorithms.