5.	Recommendations I.440, I.441, I.450, I.451 and I.452

5.1	Recommendation I.440 - ISDN user-network interface data link layer - general aspects (see Recommendation Q.920, Volume VI, Fascicle of the Blue Book)

5.2	Recommendation I.441 - ISDN user-network interface, data link layer specification (see Recommendation G.921, Volume VI, Fascicle of the Blue Book)

5.3	Recommendation I.450 - ISDN user-network interface layer 3 - general aspects (see Recommendation Q.930, Volume VI, Fascicle of the Blue Book)

5.4	Recommendation I.451 - ISDN user-network interface layer 3 specification for basic call control (see Recommendation Q.931, Volume VI, Fascicle of the Blue Book)

5.5	Recommendation I.452 - ISDN user-network interface layer 3 specification - generic procedures for the control of the ISDN supplementary services (see Recommendation Q.932, Volume VI Fascicle of the Blue Book).