Abstract: A synchronous data transmission system includes modems and data packet switches having interfaces in compliance with CCIT recommendation V24. However, verification of correct operation of the modems is preferably carried out by the system control center by transmission of control instructions which are asynchronous, such as Hayes instructions. To make this possible without requiring additional circuitry, the modems are of the bi-mode type, having a synchronous and an asynchronous mode, and during control of a modem the interface circuits at the relevant packet switch are set to the asynchronous mode. The modem detects that condition of the packet switch interface circuit, and sets its own interface circuits to correspond therewith. The interface circuits are then reset to the synchronous mode after completion of the control operation.

Abstract: An arrangement by which a sinusoidal wave is modulated in phase and amplitude in response to groups of bits includes an input (1) for receiving the groups of bits, a phase shifting circuit (5, 7) for producing two phase-shifted components of the wave and a modulating circuit for modulating the amplitude of the two components as a function of the groups. The modulating circuit includes a ROM (25), addressed by part of the n bits of the bit groups for producing an initial amplitude value, and a calculating unit (30) for obtaining final amplitude values by changing original values according to the remaining part of the bits of the bit groups.

Abstract: A voice signal coding method is provided for processing the residual base-band signal provided by a Voice Excited Predictive (VEPC) Coder. The residual signal is split over several sub-bands and the contents of each sub-band is dually coded by using a process including a simultaneous direct BCPCM and differential APC coding with dynamic assignment of the quantizing bits according to the relative sub-band contents, which simultaneous coding is followed by a dynamic choice of the sub-band coded output providing the lowest coding error.