Telephony devices, such as telephones, analog fax machines, and data modems, have traditionally utilized circuit-switched networks to communicate. With the current state of technology, it is desirable for telephony devices to communicate over the Internet, or other packet-based networks. Heretofore, an integrated system for interfacing various telephony devices over packet-based networks has been difficult due to the different modulation schemes of the telephony devices. Accordingly, it would be advantageous to have an efficient and robust integrated system for the exchange of voice, fax data and modem data between telephony devices and packet-based networks.
An echo canceller is a device that removes the echo present in a communication signal, typically by employing a linear transversal filter. Due to non-linearities in hybrid and digital/analog loops and estimation uncertainties, linear cancellers cannot entirely remove the echo present. A non-linear device, commonly referred to as a non-linear processor (NLP), can be used to remove the remaining echo. This device may be a variable loss inserted into the system, a device that removes the entire signal and injects noise with the correct level, and possibly the correct spectrum, or a combination thereof.
Existing echo cancellers in packet voice communication devices endeavor to suppress echo in the ingress signal, that is, the signal that the device sends out over the network. This is typically an echo of the egress signal (the signal that the device receives from the network) that occurs at the device. However, many packet voice transceivers do not have echo cancellers. When a first packet voice transceiver is communicating with a second packet voice transceiver over a network and the second device does not employ echo cancellation on its ingress signal, the first device may receive an egress signal transmitted by the second device that contains echo. Thus it would be advantageous to be able to efficiently suppress echo that is present in such an egress signal. However, cancellation of echo present in the egress signal is problematic because the echo path includes a round-trip journey over the communication network, as well as all of the processing performed on the signal by the packet voice transceiver at the other end of the network.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art through comparison of such systems with the present invention as set forth in the remainder of the present application with reference to the drawings.