B.S.T.J. Briefs: Use of Variable-Quality Coding and Time-Interval Modification in Packet Transmission of Speech

B.S.T.J. BRIEFS Use of Variable-Quality Coding and Time-Interval Modification in Packet Transmission of Speech By S. A. WEBBER, C. J. HARRIS, and J. L. FLANAGAN (Manuscript received December 14, 1976) Speech transmission by switched digital packets offers several opportunities for increasing the utilization of transmission capacity. We comment here upon a combination of variable-quality coding and time-interval modification that can efficiently load a transmission facility and accommodate fluctuating demands on it. Consider, typically, that a conventional voice switch detects speech energy bursts and demarks each as a packet. A time stamp is given to each packet, and the interburst silences are discarded. Each packet is digitally encoded with a quality that reflects service demands being made on the transmission facility at the moment. Coding bit rate and timestamp are written in the header data for each packet, along with necessary supervisory information, such as destination and source addresses. Successive packets are assembled in a transmit buffer and are transmitted when capacity is available. Figure 1 illustrates the process. At the receiver, arriving packets are accepted into a receive buffer. The receiver decodes each packet (in accordance with the header bit rate), reassembles the packets in temporal order (according to the time-stamp), and reinserts the silent intervals, not necessarily exactly as in the original, but with a variation that is perceptually acceptable.