Data Race, Inc.

Edwin A Bertness

David C Oliver

A system and method for compensating for slight variances between a first rate at which a far end modem transmits a series of data frames to a near end modem and a second rate at which the near end modem requires reception of the series of data frames. The modems comprise a data pump which receives data frames from the other modem at the first rate on a telephone line. The data frames are received by a data pump which provides the frames a character at a time to a controller coupled to the data pump. The controller places the characters into a pair of frame buffers in a memory coupled to the controller. The controller receives data frames from a vocoder at the second rate to be transmitted to the other modem. The controller attempts to provide data frames to the vocoder at the second rate in order to avoid distortion in the data frame flow, in particular, distortion in the compressed speech. The method comprises determining according to the second rate if a next data frame in the series of data frames has been received and providing the next data frame to a decoder if the next data frame has been received, but providing a filler frame to the decoder if the next data frame has not been received. The modem repeatedly performs these steps for each of the data frames in the series of frames. Preferably the data frames are compressed speech frames and the decoder is a vocoder for decoding the compressed speech frames. Preferably, the filler frame comprises a quiet frame which has been produced by recording essentially silence, i.e., only white noise. Preferably, the modems comprise DSVD modems. The modem also determines if the next data frame is bad if the data frame has been received and provides a filler frame to the decoder if the next data frame is bad.

System and method for handling underrun of compressed speech frames due

A system and method for performing far end echo suppression of compressed speech frames in a telecommunications system. The system comprises a client modem and a server modem coupled together via a communications path. A controller in the server modem receives a first series of compressed speech frames from the client modem and provides the frames to a vocoder. Each of the frames includes voice encoded speech parameters. The controller maintains a history of a volume parameter value of the most recently provided frames to the vocoder. The vocoder decompresses the first frames to produce a first speech signal for transmission onto a telephone line. An echo of the speech signal may occur due to impedance mismatches between a hybrid in the server modem and the telephone line. The echo is received by the vocoder along with a second subscriber's speech signal from the telephone line. The echo and second speech signal are compressed by the vocoder into a second series of compressed speech frames which are provided to the controller. In particular, one of the parameters is a volume parameter whose value indicates the energy in the speech which was compressed. The controller compares the volume parameter value of each of the frames it receives from the vocoder to the volume parameter value of a frame in the history, i.e., a frame previously provided to the vocoder, to determine if the echo is present. If the echo is present, the controller substitutes a quiet frame for the echo-laden frame in order to suppress, or squelch, the echo prior to transmitting the second series of frames to the client. In one embodiment, comparing the volume parameters comprises calculating a ratio of the volume parameter of the frame received from the vocoder with the volume parameter value in the history and determining if the ratio is less than a predetermined value.

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San Antonio, TX, United States of America

Edwin A Bertness