QoS in the field of convergence (digital broadcast, radiocom and multimedia) is highly critical and a set of parameters and related measurements methods are standardized. Nevertheless, their interpretation and exploitation are considered sensitive in the sense that they require a high level of expertise. This is mainly due to existing relationships among the long list of parameters, which have not been yet clearly identified. Our work emphasizes relationships among standardized parameters aiming at synthesising QoS into 3 relevant parameters. These relationships were established by two different approaches based on: - A statistical exploitation of a database representing the behaviour of digital TV networks, measurement equipment and supervision systems when facing difficult but realistic work conditions; - A formal modelling of parameters using the B event-based method and resulting of an incremental proof-based development based on the refinement technique and integrating a mechanical support for carrying proofs.