This Recommendation specifies the protocol to be used between a Data Terminal Equipment (DTE) and a Packet Switched Public Data Network (PSPDN), when the access is made by a dedicated circuit. In reference to the OSI model, three layers are described: the physical layer, the data link layer and the packet layer. The service offered is compliant with the OSI network service and permits the transmission of data without loss nor duplication. The access speeds and the throughputs may go up to 2 Mbit/s.