The Abstract Transport Specification provides models and mechanism for plug and play interoperability.
This document describes a set of minimal requirements that a messaging infrastructure specification must meet to be considered for inclusion in the standard. It also lists features which are optional but of interest to the HL7 community. Functional characteristics include: mechanisms for reliable messaging; Destination delivery assurances, support for HL7 version 2 composite messages, message encryption and end-point authentication.
See http://www.hl7.org/implement/standards/product_brief.cfm?product_id=385 for more information.