packet loss concealment (PLC) definition

Packet loss concealment (PLC) is a technology designed to minimize the practical effect of lost packets in digital communications. In particular, PLC is used in Voice over Internet Protocol (VoIP).

PLC mitigates against the effects of packet loss, which is the failure of one or more transmitted packets to arrive at their destination. This event can cause noticeable effects in all types of digital communications. Packets delayed for a brief time can be dealt with at a given destination by means of a buffer that stores incoming packets for a certain interval and assembles them after that interval has elapsed. Although this method increases the latency, it is often an acceptable alternative to ignoring the delayed packets altogether.

A more serious problem occurs with long-delayed or dropped packets. One method of PLC that can be effective in such situations is artificial regeneration of the packet received prior to the lost one, followed by insertion of the duplicated packet into the gap. In another technique, the digital value of the dropped packet is estimated by interpolation and an artificially generated packet inserted on that basis.

Packet loss concealment becomes more difficult to implement effectively as the ratio of dropped packets to total packets increases. When multiple consecutive packets are dropped, PLC is less effective than in cases where a single packet is delayed or missing.

This was first published in May 2007

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