ISO 10021 — X.400(88): A tutorial for those familiar with X.400(84)

Abstract

Abstract Joint work by ISO and CCITT has produced a revised version of the CCITT X.400(84) series of Recommendations. This is currently undergoing its DIS ballot in ISO, and is expected to become both an International Standard and a CCITT Recommendation in October/November 1988. The structure and current status of these documents is outlined. This tutorial reviews the significant changes from the 1984 CCITT X.400 series. The new modelling technique using the Abstract Service Definition Conventions will be the most obvious change, but this is intended to add precision to the definition of the services and not to change the underlying protocols. The addition of new functional components—the Message Store, and Access Units to Telematic and Physical Delivery Services—and the (ISO) private domain interconnectability are described. An extension mechanism has been introduced defining the treatment of extensions and thus enabling MTAs to treat unknown extensions in a consistent manner. This mechanism has been used for P1 extensions adding Distribution Lists; allowing use of ISO 9495/X.500 Directory Names; providing Redirection capabilities; adding Secure Messaging services; and providing for delivery to physical (i.e. paper) recipients. In P2 there is a heading extension mechanism, but the most important enhancement is the ability to define new body part types. Finally, the current differences between the ISO Standard and corresponding CCITT Recommendations are viewed.