An ISDN is intended to support a wide range of new and existing terminals (TE1, TE2 + TA, NT2) of variouscapabilities and designed for different access interfaces.This is necessary to permit a full application of the ISDNservice potential.The purpose of this Recommendation is to provide direction to the potential functional requirements which may be called upon for any specific terminal. The terminal functions used are more specific examples of the generalfunctions described in Recommendation I.310.In this issue of the Recommendation, it is primarily directed at the TE1and TA devices operating at the basic rate.