Overview
ISO/IEC 10588:1993 specifies how the X.25 Packet Layer Protocol (PLP, ISO/IEC 8208) is used together with X.21 / X.21 bis interfaces to provide the OSI Connection‑mode Network Service (CONS). The standard applies where X.21/X.21 bis is used (including ISDN terminal adaptors per X.30) or where circuit‑switched public or private data networks (CSDNs) appear in the path. It defines the mapping of CONS primitives and parameters to and from the protocol elements of X.25 PLP and X.21, and provides additional provisions needed when circuit‑switched connections are introduced between DTEs or between a DTE and a PSDN.
Key topics and requirements
- Scope and configurations
- Covers DTE‑to‑DTE (direct or via concatenated CSDNs or ISDN + TA) and DTE‑to‑PSDN scenarios.
- Supports both DTE/DTE and DTE/DCE modes of ISO/IEC 8208.
- Mapping of CONS to X.25/X.21
- Specifies how OSI CONS primitives and parameters map to X.25 PLP elements (as required by CCITT Rec. X.223 / ISO 8878).
- Includes mappings for error/clearing conditions - e.g., X.21 call progress signals mapped to CONS N‑DISCONNECT reason codes.
- Control of underlying connections
- Distinguishes leased (permanent) circuits and circuit‑switched (call‑oriented) connections.
- Requires use of X.21 / X.21 bis procedures to establish circuit‑switched links before invoking X.25 procedures when a circuit is not already present.
- Defines behavior on disconnection/failure (how layer‑1 failures map to N‑DISCONNECT indications).
- Layer constraints
- Data link layer constrained by ISO 7776 (LAPB) procedures.
- Network layer constrained by ISO/IEC 8208 (X.25 PLP) procedures.
- Identification and interworking
- Notes requirements for identification exchange (billing/security) and refers to X.32 methods when applicable.
- Compatibility
- Identical text published as CCITT Recommendation X.613; intended to work together with X.223 / ISO 8878 and related CCITT/ITU‑T recommendations.
Applications and who uses it
- Network engineers and architects designing or maintaining legacy packet/circuit interworking (X.25 over circuit‑switched links).
- Vendors of ISDN terminal adaptors (X.30 TAs), DTE/DCE equipment, and equipment supporting X.21/X.21 bis interfaces.
- Service providers and integrators ensuring interoperability between CSDNs, ISDNs and PSDNs when providing OSI CONS.
- Test and certification labs verifying correct mapping of CONS primitives, handling of connection setup/teardown, and failure semantics.
Related standards
- ISO/IEC 8208 - X.25 Packet Layer Protocol (PLP)
- ISO 7776 - X.25 LAPB data link procedures
- CCITT Rec. X.223 / ISO 8878 - Use of X.25 to provide OSI CONS
- CCITT Rec. X.21, X.21 bis, X.30, X.31, X.32 - interfaces and ISDN terminal adaptor support
Keywords: ISO/IEC 10588, X.25 PLP, X.21, X.21 bis, OSI Connection‑mode Network Service, CONS, CSDN, ISDN, X.30, ISO/IEC 8208, LAPB, network interworking, packet over circuit.