VoIP Voice and Fax Signal Processing

10.5 ADAPTIVE JITTER BUFFER

Adaptive jitter buffers can take several inputs and can arrive at the best possible packet delivery while maintaining least possible buffering delay. Several algorithms for AJB exist [Ramjee et al. (1994), Pinto and Christensen (1999), Tseng et al. (2004), Moon et al. (1998)]. In this section, some popular AJB concepts are given. Each algorithm has several microlevel details and extra proprietary operational steps. The appropriate algorithm for playout delay adjustment should be chosen based on the requirements of the deployment conditions, quality goals, and available parameters from RTCP, RTCP-XR, and QoS. In a wireless environment, the network and the end-terminal conditions change frequently, and hence, a faster adaptive algorithm based on per packet interval has to be chosen. The playout adjustment algorithms are of two types based on packet adjustments.

1. Talk-spurt based—adjusts adaptively during silence periods.
2. Non-talk-spurt based—adjusts on a per-packet basis or at regular time intervals.

10.5.1 Talk-Spurt-Based Adjustments

Talk-spurt is a significant speech zone. A talk-spurt is defined as a continuous section of speech at least 300 ms in duration, containing no silent period longer than 200 ms [ITU-T-P.862(2001)]. Talk-spurt is referred to as an utterance in voice quality measurement such as P.862. As shown in Fig. 10.4(a) with tile diagram markings, talk-spurts or utterances in solid boxes are separated by silence regions. In VAD/comfort ...