Switching systems based on the ATM principle have outgrown the experimental stage, and are already used today in private and corporate networks, as well as in public wide area networks to provide regular service. ATM has the inherent ability to provide a common basis for transmission and switching functionality in both local and wide area networks. With the potential to support all services available today as well as those envisaged for the future, ATM holds a strong promise for network operators and end customers. To fully exploit this potential, ATM switch architectures are required which provide versatility and modularity in supporting services and protocols, independent scalability of data throughput and control performance over a wide range, and also reliability features adaptable to the respective application scenario. This paper describes in some detail how the MainStreetXpress core services node, which has evolved from the prototype described by Fischer et. al. (1991) to a mature central office ATM switch, addresses these issues and provides a future-proof architecture incorporating all of the features required in the B-ISDN era.