Link Access Protocol Balanced (LAPB) Extended for Half-Duplex Physical Level Facility - Terminal Equipment and Protocols for Telematic Services (Study Group VIII) 7 pp
Figure 1/T.71 shows the half-duplex transmission module (HDTM) for extending the use of LAPB for operation of Teletex terminals connected to the PSTN where use of half-duplex 2400 bit/s modems is planned.