VoIP Voice and Fax Signal Processing

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 t_i, it will arrive at a_i, stay in the jitter buffer, and be played out at time p_i. The packets will take a minimum fixed delay of D_prop. In normal situations, packets will arrive in the arrival limits of a_imin to a_imax. In theory, jitter buffer has to keep the span to the extent of a_imax–a_imin. In Fig. 10.7, playout p_i is shown to coincide with a_imax. When packets arrive at a delay of more than p_i, 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 ...