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Telephony (təˈlɛfəni ) is the field of technology involving the development, application, and deployment of telecommunication services for the purpose of electronic transmission of voice, fax, or data, between distant parties. The history of telephony is intimately linked to the invention and development of the telephone. Telephony is commonly referred to as the construction or operation of telephones and telephonic systems and as a system of telecommunications in which telephonic equipment is employed in the transmission of speech or other sound between points, with or without the use of wires. The term is also used frequently to refer to computer hardware, software, and computer network systems, that perform functions traditionally performed by telephone equipment. In this context the technology is specifically referred to as Internet telephony, or voice over Internet Protocol (VoIP). Overview The first telephones were connected directly in pairs. Each user had a separate

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Adaptive Delay Aware Error Control for Internet Telephony

Catherine Boutremans, Jean-Yves Le Boudec

Forward Error Correction copes with packet losses, but at the expense of an increase of the end-to-end delay. By failing to take this into account, existing error control schemes for audio often lead to end-to-end delays larger than 150 ms, which has an impact on the perceived audio quality. In this paper, we develop an adaptive error control scheme for audio which is delay aware, i.e. which incorporates the impact on the end-to-end delay in the choice of FEC. To this end, we model the perceived audio quality as a function of the end-to-end delay and of the encoding rate at destination. We develop a joint rate/error/delay control algorithm which optimizes this measure of quality and is TCP-Friendly. We show that our scheme increases utility in a single class best effort network. We evaluate the benefit for audio sources to use the Alternative Best Effort service, which offers applications the choice between lower end-to-end delay and more overall throughput.

2001

Adaptive joint playout buffer and FEC adjustement for Internet Telephony

Catherine Boutremans, Jean-Yves Le Boudec

We develop a joint playout buffer and Forward Error Correction (FEC) adjustment scheme for Internet Telephony that incorporates the impact of end-to-end delay on the perceived audio quality. We show that it provides a better quality than the adjustment schemes for playout buffer and FEC that were previously published. This is important because of a threshold effect when the end-to-end delay of interactive audio is around 150 ms. We represent the perceived audio quality as a function of both the end-to-end delay and the distortion of the voice signal. We develop a joint rate/error/playout delay control algorithm which optimizes this measure of quality and is TCP-Friendly. It uses a channel model for both loss and delay. We validate our approach by simulation and show that (1) our scheme allows a source to increase its utility by avoiding increasing the playout delay when it is not really necessary, (2) it performs better than direct combinations of existing algorithms in the cases where end-to-end delay is important and (3) adaptive delay aware FEC adjustment brings significant improvements only if it is coupled with an adaptive playout adjustment.

2002

Adaptive Joint Playout Buffer and FEC Adjustment for Internet Telephony

Catherine Boutremans, Jean-Yves Le Boudec

We develop a joint playout buffer and Forward Error Correction (FEC) adjustment scheme for Internet Telephony, which incorporates the impact of end-to-end delay on the perceived audio quality. We show that it provides better quality than the adjustment schemes for playout buffer and FEC that were previously published. This is important because of a threshold effect when the end-to-end delay of interactive audio is around 150 ms. We represent the perceived audio quality as a function of both the end-to-end delay and the distortion of the voice signal. We develop a joint rate/error/playout delay control algorithm that optimizes this measure of quality and is TCP-Friendly. It uses a channel model for both loss and delay. We validate our approach by simulation and show that (1) our scheme allows a source to increase its utility by avoiding an increase of the playout delay when it is not really necessary, (2) it performs better than direct combinations of existing algorithms in the cases where end-to-end delay is important and (3) adaptive delay aware FEC adjustment brings significant improvements only if it is coupled with an adaptive playout adjustment.

2003

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Voice over Internet Protocol (VoIP), also called IP telephony, is a method and group of technologies for voice calls, the delivery of voice communication sessions over Internet Protocol (IP) networks,

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