AS/NZS 3621:1994

Specifies the procedures, formats and facilities at the packet layer for data terminal equipment (DTE) operating in conformance with CCITT Recommendation X.25 (1988). Virtual call and permanent virtual circuit modes of operation are covered, as are the additional packet layer procedures necessary for two DTEs to communicate directly over a dedicated path, a switched-circuit connection or a local area network. This Standard contains the necessary provisions for compatibility with 1984 and 1990 versions of X.25. This Standard is identical with, and has been reproduced from ISO/IEC 8208:1990; technical Corrigendum 1:1992; amendment 1:1990, Alternative Logical Channel Identifier assignment; amendment 3:1991, Conformance requirements; and Technical Corrigendum 1:1993 of Amendment 3:1991.

This International Standard specifies the procedures, formats and facilities at the Packet Layer for Data Terminal Equipment (DTE) operating in conformance with CCITT Recommendation X.25. Both Virtual Call and Permanent Virtual Circuit modes of operation are covered.The Packet Layer protocol specified herein can be used in both Open Systems Interconnection (OSI) and non-OSI environments. When used within the context of OSI, the Packet Layer protocol is encompassed in the Network Layer of the OSI Reference Model, ISO 7498.This International Standard covers DTE operation at the Packet Layer when accessing a public or private packet-switched network conforming to CCITT Recommendation X.25 by means of a dedicated path or a circuit-switched connection. It also covers the additional Packet Layer procedures necessary for two DTEs conforming to this International Standard to communicate directly (i.e., without an intervening packet-switched network) over a dedicated path, a circuit-switched connection, or a local area network (LAN).This International Standard also covers private networks that use CCITT Recommendation X.25 to connect to packet-switched public data networks and they may also offer an X.25 interface to a DTE (see annex A).The first edition of this International Standard was based on the 1984 CCITT Red Book text of Recommendation X.25. It also contained the necessary provisions for compatibility with the earlier 1980 CCITT Yellow Book text of Recommendation X.25. This second edition is based on the 1988 CCITT Blue Book text of Recommendation X.25. Retained within this second edition are the necessary provisions for compatibility with the 1984 and 1980 versions of X.25. The differences between the first and second editions of this International Standard are summarized in annex B.It should be noted that this International Standard and CCITT Recommendation X.25 as it applies to DTEs are different in scope. This International Standard contains the specifications that Recommendation X.25 places on DTEs. In addition, this International Standard contains added specifications to facilitate interworking between DTEs and to cover direct DTE-to-DTE operation. This broader scope has to be recognized in the application of this International Standard.

First published in Australia as AS 3621-1989.
First published in New Zealand as NZS/ISO 8208:1987.
AS 3621-1989 and NZS/ISO 8208:1987 jointly revised, amalgamated and designated as Joint Standard AS/NZS 3621:1994.