ENV 41901:1987

Information systems interconnection - X.29-mode procedures between a packet mode DTE or a PAD and a PAD via a public or private X.25 packet switched network or ISO 8208 packet level entity and ISO 7776 link level entity - X.3 character-mode access via a public or private PAD attached to an X.25 packet switched network or ISO 8208 packet level entity and ISO 7776 link level entity - X.28 character-mode access via a telephonic circuit or data circuit to a PAD