- Circuit-based Access Services
The Circuit-based Access Services provide the delivery or exchange of raw user data, via fractional access to digital lines (circuits), e.g. ISDN BRI, fractional E1, etc. These services are provided directly to the end-user appliance (e.g. an ISDN phone) through terminal adapters, channel service units / data service units (CSU/DSU), multiplexers, etc., which in turn interface to Transport Services (after aggregation with other Access Services), or directly to Transmission Services (e.g. ISDN port of an Inmarsat satcom terminal).