Abstract
Commonly understood as the next generation networks (NGN), a composite environment of proven telecommunications and Internet-oriented mechanisms has become generally recognized as the telecommunications environment of the future. However, the nature of the NGN environment presents several complex issues regarding quality assurance that have not existed in the legacy environments (e.g., multi-network, multi-vendor, and multi-operator IP-based telecommunications environment, distributed intelligence, third-party provisioning, fixed-wireless and mobile access, etc.). In this chapter, a serviceaware policy-based approach to NGN quality assurance is presented, taking into account both perceptual quality of experience and technology-dependant quality of service issues. The respective procedures, entities, mechanisms, and profiles are discussed. The purpose of the presented approach is in research, development, and discussion of pursuing the end-to-end controllability of the quality of the multimedia NGN-based communications in an environment that is best effort in its nature and promotes end user’s access agnosticism, service agility, and global mobility.
TopQuality Mechanisms
The measure of system performance represents one of the basic evaluation criteria of a successful network, solution or a service from nearly all viewpoints: deployment, operation, and customer satisfaction. In general referred to as the quality, there are basically two approaches to defining, measuring and assessing the success of meeting a specific set of requirements or an expected behaviour (DSL Forum, TR-126, 2006).
The measure of performance from the network perspective is known as the quality of service (QoS) and involves a range of QoS mechanisms that are implemented for the purpose of meeting the defined conditions in the network. Typically, QoS metrics include network operation parameters (i.e., bandwidth, packet loss, delay, and jitter). On the other hand, the measure of performance as perceived from the end user is known as the quality of experience (QoE) and addresses the overall satisfaction of the end user and the ability to meet their expectations.
While the QoS is rather objective approach to assessing the success of performing within a specified network subsection, the QoE is subjective, measured on an end-to-end basis, and involves human-related criteria, based on which certain descriptive indexes of performance are set. Some examples of QoE metrics are the mean opinion score (MOS), degraded seconds, errored seconds, unavailable seconds, etc.
In essence, there are three layers of a service environment that should be considered in terms of quality in any type of telecommunications environment:
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The service exposure layer, representing the final point of QoE measurements toward the end user.
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The application layer, realizing and shaping the service through various application layer service parameters (i.e., media resolution, codec types, bit rate, error correction mechanisms, etc.).
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Transport (network) layer, potentially inducing various impairments (i.e., losses, delay, jitter, and employing the respective QoS mechanisms).