be transmitted in the case of heavy traffic conditions of the network the reduction of the network load will prevent a severe loss of quality of the transmitted speech signal under such heavy traffic conditions the frame 28 according to fig2 comprises a header 30 for transmitting necessary properties of said frame it comprises the actual number of prediction coefficients transmitted in the portion 32 reserved for the representation of the prediction coefficients alternatively it can also state the number of bits used for each prediction coefficient the portions 34 36 in the frame represent the excitation signal because in a celp coder the frame of signal samples may be subdivided in m sub frames each with its own excitation signal m portions are present in the frame to represent the excitation signal for the complete frame in the receiver 8 the input signal is applied to an input of a decoder 40 optionally via a bitrate reducer 38 in the decoder 40 outputs of a bitstream deformatter 42 are connected to corresponding inputs of a parameter decoder 44 a first output of the parameter decoder 44 carrying an output signal c p representing p prediction parameters is connected to an input of an lpc coefficient interpolator 46 a second output.