European digital cellular telecommunications system (Phase 2) - Mobile Station - Base Station System (MS-BSS) interface - Data Link (DL) layer specification; English version ETS 300555:1994
Edition 1995-01

Integrated Services Digital Network (ISDN) - Digital Subscriber Signalling System No. one (DSS1) protocol - Data link layer - Part 2: General protocol specification [ITU-T Q.921 (1993), modified]; English version ETS 300402-2:1995
Edition 1996-06

Integrated Services Digital Network (ISDN); user-network interface data link layer specification; application of CCITT recommendations Q.920/I.440 and Q.921/I.441; english version ETS 300125:1991
Edition 1992-05

Integrated Services Digital Network (ISDN) - Digital Subscriber Signalling System No. one (DSS1) protocol - Data link layer - Part 6: Test Suite Structure and Test Purposes (TSS&TP) specification for the general protocol; English version ETS 300402-6:1997
Edition 1997-11

Integrated Services Digital Network (ISDN) - Digital Subscriber Signalling System No. one (DSS1) protocol - Data link layer - Part 1: General aspects [ITU-T Q.920 (1993), modified]; English version ETS 300402-1:1995
Edition 1996-06