Voice Quality & Quality of Service (QoS)
QoS is a collective measure of the level of service delivered to a user. QoS can be considered as the level of assurance for a particular application that the network can meet its service requirements. From a technical perspective, QoS can be characterized by several performance criteria, such as uptime, throughput, connection setup time, percentage of successful transmissions, speed of fault detection and correction, etc. In an IP network, QoS can be measured in terms of bandwidth, packet loss, delay, and jitter. In order to provide a high QoS, the IP network needs to provide assurances that for a given session or set of sessions, the measurement of these characteristics will fall within certain bounds. High quality over IP networks requires the use of managed networks, QoS solutions, and service-level agreements between the providers. Given the stringent delay requirement voice imposes, one should look at the avenues to achieve quality, reliability and scalability of traditional telephone networks, if they want to make VoIP a fierce competitor to the traditional telephony.
For organizations that are interested in deploying VoIP technology on their corporation Intranets or on their other networks, the success of these technologies will depend on the performance of the network elements that carry and route the voice packets। The users of VoIP are concerned about the possible voice quality degradation when voice is carried over these packet networks, as the existing Internet protocols do not support real time traffic. Voice quality is the crucial factor in making VoIP acceptable to users, and it is important to understand the factors that affect the quality of the voice over the packet transmission networks, as well as to obtain the tools and optimize them. Although speech quality is often cited as one of the greatest challenges facing the development and market acceptance of voice over packet networks, people may in fact accept ‘sub-toll quality’ voice in exchange for some other benefits such as mobility, reduced cost and other advanced services VoIP can offer.
QoS is a collective measure of the level of service delivered to a user. QoS can be considered as the level of assurance for a particular application that the network can meet its service requirements. From a technical perspective, QoS can be characterized by several performance criteria, such as uptime, throughput, connection setup time, percentage of successful transmissions, speed of fault detection and correction, etc. In an IP network, QoS can be measured in terms of bandwidth, packet loss, delay, and jitter. In order to provide a high QoS, the IP network needs to provide assurances that for a given session or set of sessions, the measurement of these characteristics will fall within certain bounds. High quality over IP networks requires the use of managed networks, QoS solutions, and service-level agreements between the providers. Given the stringent delay requirement voice imposes, one should look at the avenues to achieve quality, reliability and scalability of traditional telephone networks, if they want to make VoIP a fierce competitor to the traditional telephony.
For organizations that are interested in deploying VoIP technology on their corporation Intranets or on their other networks, the success of these technologies will depend on the performance of the network elements that carry and route the voice packets। The users of VoIP are concerned about the possible voice quality degradation when voice is carried over these packet networks, as the existing Internet protocols do not support real time traffic. Voice quality is the crucial factor in making VoIP acceptable to users, and it is important to understand the factors that affect the quality of the voice over the packet transmission networks, as well as to obtain the tools and optimize them. Although speech quality is often cited as one of the greatest challenges facing the development and market acceptance of voice over packet networks, people may in fact accept ‘sub-toll quality’ voice in exchange for some other benefits such as mobility, reduced cost and other advanced services VoIP can offer.
Approach:
VIPER
To investigate the quality matters of Voice over IP a project named ‘Voice over Internet Protocol Environment for Research (VIPER)’ has been undertaken which could enable network-integrated, controllable, and statistically valid end-to-end measurements of VoIP quality. This system also enables specifications for vendors about ideal network configurations to obtain better voice quality over the Internet. Following sections discuss the specific motivations and architecture of the VIPER system. Results from VIPER testing are presented in subsequent chapters.
To investigate the quality matters of Voice over IP a project named ‘Voice over Internet Protocol Environment for Research (VIPER)’ has been undertaken which could enable network-integrated, controllable, and statistically valid end-to-end measurements of VoIP quality. This system also enables specifications for vendors about ideal network configurations to obtain better voice quality over the Internet. Following sections discuss the specific motivations and architecture of the VIPER system. Results from VIPER testing are presented in subsequent chapters.
Motivation
In performing this work, we would like to be able to determine the impact of design and environmental changes (e.g. network conditions, such as packet loss) on voice quality. The ability to quantify voice quality is important for a number of reasons. First, we would like to compare the quality of voice over packet networks to the PSTN, as the PSTN has become the de facto standard for what constitutes acceptable voice quality. We would also be able to test the effectiveness of various network protocols and policies that are known to support real time traffic. Lastly, from a business perspective, measurements of voice quality allow a vendor to offer better features than those of its competitors, as well as to provide the basis for voice quality service level agreements (SLA).
Voice quality could be measured using a procedure called Mean Opinion Scores (MOS). The MOS uses the Absolute Category Rating (ACR) procedure to determine the general acceptability or quality of voice communication systems or products. A MOS measurement is made by having a group of listeners rank a speech sample on a scale of 1-5, where 1 is very bad, 5 is excellent and 4 is normally considered ‘toll-quality’ (what one hears on the Public Switched Telecommunications Network (PSTN)). Obviously MOS is highly subjective and not highly reproducible. It is difficult to assemble a group of people, creation of ideal test facilities, selection of proper sound files, assembling audio devices and it is not suitable for long-term measurement
To address the shortcomings of this subjective testing a number of methods have been developed to create an objective and reproducible measurement of perceived voice quality. There are two clarity measurements currently used, the first one is PSQM (Perceptual Speech Quality Measurement) developed by KPN Research and the second one is PAMS (Perceptual Analysis/Measurement System) developed by British Telecom. Both these techniques use natural speech or speech-like samples as their inputs. The speech samples are played over the network that is setup for different configurations and the received speech sample is compared with the original speech sample using clarity algorithms.
In performing this work, we would like to be able to determine the impact of design and environmental changes (e.g. network conditions, such as packet loss) on voice quality. The ability to quantify voice quality is important for a number of reasons. First, we would like to compare the quality of voice over packet networks to the PSTN, as the PSTN has become the de facto standard for what constitutes acceptable voice quality. We would also be able to test the effectiveness of various network protocols and policies that are known to support real time traffic. Lastly, from a business perspective, measurements of voice quality allow a vendor to offer better features than those of its competitors, as well as to provide the basis for voice quality service level agreements (SLA).
Voice quality could be measured using a procedure called Mean Opinion Scores (MOS). The MOS uses the Absolute Category Rating (ACR) procedure to determine the general acceptability or quality of voice communication systems or products. A MOS measurement is made by having a group of listeners rank a speech sample on a scale of 1-5, where 1 is very bad, 5 is excellent and 4 is normally considered ‘toll-quality’ (what one hears on the Public Switched Telecommunications Network (PSTN)). Obviously MOS is highly subjective and not highly reproducible. It is difficult to assemble a group of people, creation of ideal test facilities, selection of proper sound files, assembling audio devices and it is not suitable for long-term measurement
To address the shortcomings of this subjective testing a number of methods have been developed to create an objective and reproducible measurement of perceived voice quality. There are two clarity measurements currently used, the first one is PSQM (Perceptual Speech Quality Measurement) developed by KPN Research and the second one is PAMS (Perceptual Analysis/Measurement System) developed by British Telecom. Both these techniques use natural speech or speech-like samples as their inputs. The speech samples are played over the network that is setup for different configurations and the received speech sample is compared with the original speech sample using clarity algorithms.
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