This Recommendation defines the different categories of access for data terminal equipment to the different data transmission services provided by public data networks (PDNs) as defined in Recommendation X.2 and by ISDNs (including through Terminal Adaptors) as defined in Recommendations X.30 (I.461) X.31 (I.462) and the I.230 series@ namely: i) circuit switched data transmission services; ii) packet switched data transmission services; iii) leased circuit data transmission services. The categories of access described in this Recommendation take into account direct connections (see Note) to public data networks and ISDNs and the various access cases where interworking with other public networks is involved. Access to the packet switched data transmission service via the PAD function as defined in Recommendation X.3 is also covered in this Recommendation. Note ?C Direct connections may be provided by means of leased circuits or by dedicated access circuits.