Subscribers who use long-distance communication services expect from it the usual “telephone” quality. The quality of voice communication is a key success factor in this sphere.
While choosing the VoIP provider, one should take into account and ask the candidates about the QoS, the company provider should be competent in the development of technologies and protocols that improve the quality of voice in IP networks. The following sections of this document describe the functions and methods that determine the quality of voice transmission and play an important role in developing quality services.
What is the quality of speech?
The quality of speech is usually called the subjective quality of the voice during a call. However, usually when referring to speech quality, refer to the results of the listening test, which may not take into account the quantitative factors, for example, delay. Typical assessments of speech quality are the average score of speech intelligibility (mean opinion score, MOS), the measure of the quality of continuous speech (perpetual speech quality measure, PSQM), or perceptual evaluation of speech quality (PESQ), or R-factor.
Quality of speech in corporate and operator networks
Developers of the IP-protocol originally intended to use it for data exchange, and not for VoIP wholesale termination in real time. Therefore, packets of the same information flow are routed independently of each other and the processing time in the nodes has a wide spread. At peak load of communication channels, there is no guarantee that voice packets will not be idle in queues or will receive a higher priority in comparison with less sensitive to delays data. To resolve this problem, IP-based networks use mechanisms that guarantee the required quality of service (QoS). At the moment, there are three main approaches to providing the required level of service in real time. This is the reservation of resources, i.e., when resources reserved for the application work are reserved for the duration of the session; Prioritization of traffic, or its division into classes with the subsequent prioritization of the order of service; And re-routing, i.e., transfer of traffic to a backup route when the network is overloaded.
To implement these methods, Integrated Services (IntServ) and Differentiated Services (DiffServ) technologies are implemented using the Resource ReSerVation Protocol (RSVP). Each of them has its own features and scope. Here we will talk about this and other methods.