DECnet-Plus

This manual, "DECnet-Plus DECnet-Plus OSAK Programming" (November 1996), serves as a programming guide for using the OSAK (OSI Applications Kernel) interface to develop OSI (Open Systems Interconnection) applications.

Key aspects covered include:

1. OSAK Programming Interfaces: It details how to use three distinct programming interfaces:

   • Application Programming Interface (API): For accessing services of the Session, Presentation, and ACSE (Application Control Service Element) layers.
   • Remote Operations Service Element (ROSE) API: For developing interactive distributed applications based on the ROSE protocol, handling encoding and decoding of ROSE Protocol Control Information (PCI).
   • Session Programming Interface (SPI): For direct access to services of the OSI Session layer, supporting different session versions and data limits.

2. OSI Networking Concepts: Provides foundational knowledge of the OSI seven-layer model, with a focus on the upper layers (Application, Presentation, Session) that OSAK implements. It covers concepts like application entities, presentation contexts (abstract and transfer syntax, ASN.1), connections and associations, data types (user, capability, expedited, typed), and information exchange mechanisms (activities, functional units, synchronization points, tokens, data segmentation, exception reports).

3. Application Development Guidance:

   • Planning: Offers a checklist for designing applications, including memory management (static/dynamic allocation, user buffers, workspace), addressing needs (presentation addresses, transport templates, NSAPs, multihoming), choosing between single or multiple associations, and considerations for portability across operating systems.
   • Core Tasks: Explains the steps for writing an OSAK application, such as preparing parameter blocks and user buffers, setting up and releasing associations/connections, and sending data.
   • Event Handling: Describes methods for receiving inbound events, including polling, blocking, and asynchronous event notification (OpenVMS only).
   • Association Redirection: Discusses using the redirect service to distribute incoming associations among local processes.
   • Linking: Provides specific instructions for linking OSAK applications on Digital UNIX, ULTRIX, and OpenVMS systems.

4. OSAKtrace Utility: Introduces OSAKtrace, a tool for capturing and analyzing OSI information exchange to verify application conformity with standards and identify problems. It describes its components (trace emitter, trace analyzer), methods for enabling tracing, running the analyzer, and interpreting its output at various OSI stack levels (Transport, Session, Presentation, ACSE, User).

The manual is intended for OSI application programmers who understand the upper-layer OSI standards implemented by Digital's OSAK product. It supports OpenVMS VAX 7.1, OpenVMS Alpha 7.1, and Digital UNIX 4.0 operating systems, and DECnet-Plus and OSAK Version 3.0 software.