12. An apparatus for use in suppressing acoustic echo from a reference speech signal in a target speech signal, the target speech signal and the reference speech signal each being transmitted through a packet-based communications network and each having been encoded with a speech coder which generates speech parameters, the target speech signal comprising a sequence of target packets and the reference signal comprising a sequence of reference packets, the apparatus comprising: an energy estimator which estimates one or more reference speech energy levels in one or more reference packets based on one or more of said speech parameters generated by said encoding of said reference signal, the speech parameters comprising one or more linear predictive coding (LPC) coefficient parameters; an energy estimator which estimates a target speech energy level in a target packet based on one or more of said speech parameters generated by said encoding of said target signal; a comparator which compares the target speech energy level to said one or more reference speech energy levels; a spectral difference calculator which computes a spectral difference between the target packet and one or more of the reference packets based on said LPC coefficient parameters; and an echo detector which detects an echo in said target speech signal based on said comparison of said target speech energy level to said one or more reference speech energy levels and said spectral difference.
12. An apparatus for use in suppressing acoustic echo from a reference speech signal in a target speech signal, the target speech signal and the reference speech signal each being transmitted through a packet-based communications network and each having been encoded with a speech coder which generates speech parameters, the target speech signal comprising a sequence of target packets and the reference signal comprising a sequence of reference packets, the apparatus comprising: an energy estimator which estimates one or more reference speech energy levels in one or more reference packets based on one or more of said speech parameters generated by said encoding of said reference signal, the speech parameters comprising one or more linear predictive coding (LPC) coefficient parameters; an energy estimator which estimates a target speech energy level in a target packet based on one or more of said speech parameters generated by said encoding of said target signal; a comparator which compares the target speech energy level to said one or more reference speech energy levels; a spectral difference calculator which computes a spectral difference between the target packet and one or more of the reference packets based on said LPC coefficient parameters; and an echo detector which detects an echo in said target speech signal based on said comparison of said target speech energy level to said one or more reference speech energy levels and said spectral difference. 13. The apparatus of claim 12 wherein the speech coder comprises a CodeExcited Linear Prediction (CELP) coder, wherein the speech parameters include one or more excitation gain parameters and one or more linear predictive coding (LPC) coefficient parameters, and wherein the energy estimator of the one or more reference speech energy levels and the energy estimator of the target speech energy level each estimate both an excitation energy level and a LPC synthesis filter energy level.