This paper describes the implementation and validation in field trials of an ATM based HFC access network providing Quality of Service for native ATM applications and legacy IP applications. Native ATM applications are supported by Switched Virtual Connections allocating dedicated resources in the HFC network. IP applications are enriched with QoS in the HFC network by adopting the differentiated services strategy defined by IETF. The developed and in hardware implemented MAC controller supports several service classes and is capable to distribute not pre-allocated upstream bandwidth in a fair way to the bandwidth requesting cable modems by simultaneous respecting the priorities of the service classes.