Techniques for Packet Voice Synchronization

Abstract

This paper discusses several aspects of the packet voice synchronization problem, and techniques that can be used to address it. These techniques estimate in some way the delay encountered by each packet and use the delay estimate to determine how speech is reconstructed. The delay estimates produced by these techniques can be used in managing the flow of information in the packet network to improve overall performance. Interactions of packet voice synchronization techniques with other network design issues are also discussed.

Performance Evaluation of an IP Voice Terminal

“…The former uses the same playout delay throughout a talkspurt (and, as a result, faithfully reconstructs the original periodic nature of the received audio data from the sender), but allows different playout delays from one talkspurt to another. While this may result in artificially elongated or compressed silence periods, this is not noticeable in played out speech if the change is reasonably small [5]. In the latter approach, the play out delay varies from packet to packet.…”

“…Some playout algorithms (5) In this section we present 4 different play out algorithms. Algorithms 1 and 2 are originally reported in [8] and algorithm 3 is suggested in [9].…”

“…This algorithm is based on stochastic gradient algorithms used in estimation and control theory [5], and operates by estimating two statistics characterizing the network delay incurred by audio packets: the delay itself, and a variational measure of the observed delays. Each of these estimates is recomputed each time a new packet arrives.…”

Dynamic priority protocols for packet voice

“…Although average delays and delay variability are reduced by the combination of simplified protocols, short packets, and fixed routing, delay variability could be significant in a long-haul network [25]. The variable delay component is primarily due to queueing delays which tend to increase with the traffic load.…”

“…Finally, the timestamp can indicate the delay that a packet has accumulated in transit so far [25]. In this case, the timestamp might be more appropriately called a delaystamp.…”