VoIP Protocols

1.1 The rebirth of VoIP In his famous topic Crossing the Chiasm, Geoffrey A. Moore [B1] explains why so many innovative companies fail to turn their early successes into solid market positions and recurrent revenues. In an immature market, early adopters are eager to test new products and services, and they are willing to accept […]

Why beyond VoIP protocols?

1.2 The new multimedia services will need to be much more than mere technology demonstrators. In order to build a demonstrator, engineers need only focus on the functional aspects: select a protocol, make sure it has the right service primitives, and combine these primitives into the desired functionality. The companion reference to this topic, IP […]

Scope of this topic (VoIP Protocols)

1.3 Beyond VoIP Protocols is a companion reference to IP Telephony: Deploying Voice-over-IP Protocols (for more details see the last page of this topic). Both topics have been written with the goal of supporting those involved in the design and deployment of multimedia VoIP projects, and provide invaluable references for most of the required technology. […]

Conclusion (VoIP Protocols)

1.5 As with every technical topic, despite careful proof-reading, there may be errors, typing mistakes, or you may find that some important new development are missing. We welcome your feedback, which can be sent by email to topicnetcentrex.net. As technology is constantly evolving, we welcome all your suggestions for inclusion of new topics in future […]

Intended audience (VoIP Protocols)

1.4 The intended audience for Beyond VoIP Protocols is: • Network planning teams, in charge of buying transport capacity, who need to guarantee acceptable end-to-end transmission delays. • RFI/RFP technical teams who want to evaluate IP access devices (e.g., DSLAMs or BASs). The proper support for per-stream quality of service becomes fundamental in such equipment. […]

Introduction to Speech-coding Techniques (VoIP Protocols)

2.1 A primer on digital signal processing 2.1.1 Introduction At the beginning of the 20th century, all devices performing some form of signal processing (recording, playback, voice or video transmission) were still using analogue technology (i.e., media information was represented as a continuously variable physical signal). It could be the depth of a groove on […]

The basic tools of digital signal processing (VoIP Protocols)

2.2 2.2.1 Why digital technology simplifies signal processing Common signal-processing operations Signal-processing circuits apply a number of operations to the input signal(s): • Sum. • Difference. • Multiplication (modulation of one signal by another). • Differentiation (derivative). • Integration. • Frequency analysis. • Frequency filtering. • Delay. It is obvious that the sum and […]

Overview of speech signals (VoIP Protocols)

2.3 2.3.1 Narrow-band and wide-band encoding of audio signals Audio engineers distinguish five categories of audio quality: • The telephony band from 300 Hz to 3,400 Hz. An audio signal restricted to this band remains very clear and understandable, but does alter the natural sound of the speaker voice. This bandwidth is not sufficient to […]

Advanced voice coder algorithms (VoIP Protocols)

2.4 2.4.1 Adaptive quantizers. NICAM and ADPCM coders We have already mentioned that if the probability density function (PDF) of the input is known one optimal quantizer can be computed for the signal. Linear or logarithmic quantizers are time-unvarying systems: their step sizes are fixed for the entire duration of the signal. Logarithmic quantizers (such […]

Waveform coders. ADPCM ITU-T G.726 (VoIP Protocols)

2.5 Waveforms coders are also called temporal speech coders; they rely on a time domain and sample-by-sample approach. Such coders use the correlation between continuous samples of speech and are based on adaptive quantizers and adaptive (generally backward) predictors. They are very efficient in the range 40-24 kbit/s, but quality degrades quickly (around 16 kbit/s). […]