From best effort to enhanced QoS

The new communication environment has brought new requirements on the qualities of service for which the present "best effort" semantics is inadequate. The response to this evolution goes through the definition of a new model of QoS for the lower layers. In the “best effort” model, when a service provider accepts a transmission with a given QoS, it does not commit itself to any duty about the way it will take account of this QoS. The "guaranteed" QoS requires resources reservation mechanisms which are not always available. We present in this paper new negotiation rules and a new semantics for the QoS. It allows a service user to express more accurately its requirements and implies for the service provider an obligation of behaviour. 1 THE QoS MODEL The goal of this paper is to study the quality of the service offered by a transport service provider to transport service users, in a peer-to-peer connection mode service. The figure 1 represents the model that will be used in this study. The only observable events are the occurrences of transport service primitives at the two transport service access points (T-SAP). The term Quality of Service (QoS) is the collective name given to certain characteristics associated with the invocations of the service facilities as observed at the SAP. The QoS is specified in terms of a set of parameters. The ____________ * This work has been done in the framework of the RACE project 2060, CIO. 1 Research Assistant of the University of Liège performance QoS parameters, in particular, are those QoS parameters whose definition is based on a performance criterion to be assessed.