Overview
ISO/IEC 9066-2:1989 - "Information processing systems - Text communication - Reliable Transfer - Part 2: Protocol specification" - defines the protocol (abstract syntax) and procedural behaviour for the Reliable Transfer Service Element (RTSE). Part 2 specifies how RTSE protocol machines (RTPMs) interact with peer RTPMs using the Association Control Service Element (ACSE) and the presentation service, how RTPMs interact with their service‑users, and the conformance requirements for implementations. The standard is aligned with CCITT Recommendation X.228 and uses ASN.1 abstract syntax and encoding conventions.
Key topics and technical requirements
- Scope and purpose: Formal protocol definition for reliable transfer of application-protocol-data-units (APDUs) between open systems, independent of application semantics.
- Protocol elements: Defines APDUs such as RT-OPEN-REQUEST (RTORQ), RT-OPEN-ACCEPT (RTOAC), RT-OPEN-REJECT (RTORJ), RT-TRANSFER, RT-TOKEN-PLEASE, RT-TURN-PLEASE, RT-P-ABORT/RT-U-ABORT, and others used for association establishment, transfer, turn-taking and abort/error handling.
- Service mapping: Specifies how RTSE service primitives map onto ACSE services (A-ASSOCIATE, A-RELEASE, A-ABORT) and onto the presentation-service primitives (P-DATA, P-ACTIVITY-START/END, token/control services).
- ASN.1 abstract syntax & encoding: APDUs are specified in ASN.1. Depending on presentation encoding mode, APDU values are encoded as ASN.1 ANY (X.410-1984 mode) or EXTERNAL (full encoding). Basic Encoding Rules (BER) considerations are referenced.
- Procedures and state: Covers association‑establishment, release, transfer procedures, turn management, error reporting (user/provider exceptions), and recovery (transfer-resume, retry, association-recovery). Annexes include RTPM state tables and object identifier assignments.
- Conformance: Defines requirements for systems implementing the protocol to claim conformance with ISO/IEC 9066-2.
Practical applications and users
- Who uses it: Protocol implementers, middleware developers, systems integrators, vendors of messaging/text communication stacks, and standards engineers building OSI‑compliant application-layer services.
- Where applied: Implementing reliable, application‑independent text/ messaging transfer between open systems; integrating with ACSE and presentation layers in OSI stacks; legacy systems requiring compliance with established RTSE behaviour and ASN.1‑based APDU encoding.
- Value: Enables robust recovery from communication and end‑system failures while minimizing retransmission, providing well-defined semantics for association lifecycle and transfer error handling.
Related standards
Keywords: ISO/IEC 9066-2:1989, Reliable Transfer, RTSE, APDU, ACSE, presentation service, ASN.1, OSI, RT-OPEN, protocol specification, conformance.