The introduction of the concept of QoS has led to an extension of the traditional concepts of service and service specification. However, the design of QoS support is usually done without a systematic approach, leading to concepts of QoS support ranging from basic QoS monitoring capabilities to hard real-time guarantees. In more advanced QoS support, intermediate layers should be designed in a way that enables the masking or controlled handling of sporadic QoS violations. To implement this degradation path support across multiple layers, a negotiation of preferred and supportable failure semantics is a requirement. To realize these advanced QoS support features, not only new QoS control mechanisms within the layers have to be developed but the semantics of QoS negotiation protocols between layers must be better understood and subsequently extended. A framework formally based on set theory and relations is presented that allows the specification of QoS hierarchies including a well-defined failure type model. The framework supports the development of QoS negotiation protocols and can be used as a formal base for a structured system analysis.
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