Abstract: Fast scheduling mechanism of tasks to be performed in a communication system, like a modem, and the scheduler for implementing the mechanism.The communication system receives, synchronously to a rate determined by a high priority program, data to be processed by the tasks of a lower priority main program.Instead of scheduling the tasks immediately upon requests generated by an interrupt program, said tasks are scheduled with a controled delay relatively to their corresponding requests. Thus, free processing windows are created for execution of asynchronous tasks or synchronous transient overloads. Overall, more synchronous and asynchronous tasks can be performed without increasing processing power.

Abstract: The device for providing protection against echoes includes a level memory (33) for storing a value Gs and a comparator (34) for comparing the level Gx provided by an AGC device (31) upon receipt of a message with a value Gs stored in the level memory (33) and for supplying a resetting signal to the equalizer (35) for resetting the coefficients thereof to zero together with a signal for storing the level Gx as a new value Gs in the level memory (33) where Gx exceeds Gs by a predetermined value, or for supplying a signal for inhibiting the decoding of the data signals where Gx falls short of Gs by a predetermined value, thereby indicating that the received message is an echo.

Abstract: A method and device which, in a receiver forming part of a data transmission system using DSB-QC modulation and wherein the transmitter generates a first sequence of successive carrier phase changes of 180.degree. taking place at the signaling rate 1/T followed by a second sequence of pseudo-random carrier phase changes of 0.degree. and 180.degree., with the first of these being a 0.degree. phase change, permit detecting the beginning of said second sequence. The received signal is filtered to extract therefrom its components at frequencies f.sub.1 and f.sub.2 defined asf.sub.1 =f.sub.c -1/2T f.sub.2 =f.sub.c +1/2Twhere f.sub.c is the carrier frequency.The components at frequencies f.sub.1 and f.sub.2 are combined to generate a signal S of frequency 1/T. The beginning of said second sequence is determined by detecting the instant at which the energy of signal S drops below its average value.