ISO 8648:1988

Overview

ISO 8648:1988 defines an architectural model for the OSI Network Layer that serves as a formal framework for Network Layer standardization and protocol design. It maps abstract Network Layer elements (end systems, intermediate systems, subnetworks, interworking units) to “real world” components (networks, switches, transmission media), clarifies terminology, and describes how Network Layer functionality (relaying, routing, service provision) can be organized and combined. The standard is intended to support the design and application of Network Layer protocols - especially where multiple heterogeneous real networks must be interconnected to deliver a unified OSI Network Service.

Key topics

• Network Layer architecture: definitions and the internal organization of Network Layer entities, including roles and responsibilities of end systems and intermediate systems.
• Real subnetwork vs. subnetwork abstraction: distinction between physical collections of equipment and their abstract representation used by Network Layer protocols.
• Interworking units and relay systems: how equipment that performs network‑relay functions is modeled and represented.
• Service concepts: definitions for data transmission service, network-service-access-points (NSAPs), connection-mode (CO-NS) and connectionless-mode (CL-NS) services, and the relationship between Network Service and underlying real subnetworks.
• Protocol roles and classifications: roles such as subnetwork access protocols (SNAcP), subnetwork independent convergence protocols (SNICP), and subnetwork dependent convergence protocols (SNDCP); how different protocol components may cooperate or be combined.
• Interconnection scenarios: approaches for interconnecting subnetworks, single data-link or complex internetwork configurations, and considerations for hop-by-hop harmonization and internetworking approaches.
• Terminology & conventions: common terms and abbreviations for consistent use across Network Layer standards.

Note: ISO 8648 does not specify Network Layer management procedures or operational performance requirements for relay functions.

Applications

• Designing and specifying Network Layer protocols and protocol components for OSI-compliant systems.
• Mapping protocol layers to physical networks and planning internetworking between heterogeneous real subnetworks (public carriers, private networks, LANs).
• Classifying existing Network Layer protocols and clarifying overlapping functions to avoid proliferation of incompatible protocol designs.
• Guiding interoperability testing and system integration where multiple subnetworks must be interconnected to provide an OSI Network Service.

Who should use this standard

• Network architects and protocol designers
• Standards developers and technical committees
• System integrators and vendors implementing OSI Network Layer functionality
• Test labs and interoperability teams working with heterogeneous networks

Related standards

• ISO 7498 (OSI Basic Reference Model)
• ISO/TR 8509 (Service conventions)
• ISO 8348 (Network service definition) and ISO 8348/Add.1
• ISO 8208 (X.25 packet level protocol)
• ISO 8802 (LAN standards, various parts)
• CCITT/ITU-T Recommendations X.200, X.210, X.21, X.25

Keywords: ISO 8648, OSI Network Layer, Network Layer architecture, subnetwork, intermediate system, interworking unit, routing, relaying, subnetwork access protocol, internetworking.