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VoIP Voice and Fax Signal Processing by Sivannarayana Nagireddi

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10.7 AJB ALGORITHMS OVERVIEW

In the literature [Ramjee et al. (1994), Pinto and Christensen (1999)], several algorithms are explained based on the assumption—both transmitter and receiver are tracking the absolute timing information. Hence, both transmitter and receiver are mapped on the same time-scale reference. One such representation in relation to reference [Ramjee et al. (1994)] is given in Fig. 10.7. In this figure, the same symbols of [Ramjee et al. (1994)] are retained.

In Fig. 10.7, it is assumed that the sending and receiving sides maintain the same absolute timing. For a packet sent at time reference of ti, it will arrive at ai, stay in the jitter buffer, and be played out at time pi. The packets will take a minimum fixed delay of Dprop. In normal situations, packets will arrive in the arrival limits of aimin to aimax. In theory, jitter buffer has to keep the span to the extent of aimaxaimin. In Fig. 10.7, playout pi is shown to coincide with aimax. When packets arrive at a delay of more than pi, initially packets may be dropped and then jitter buffer keeps adapting to grow the jitter buffer. When the arrival time for a significant group of packets jumps (bursty delay), this can result in spiky conditions.

Jitter buffer size increases for spiky conditions, and this will result in an increase of end-to-end delay. When end-to-end delays are growing, the trade-offs would be to reduce delay at the cost of accepted packet drop. In practice, the drop and delay trade-offs ...

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