Overview
ISO/IEC 8480:1995 specifies procedures for DTE/DCE interface back-up control operation using ITU‑T Recommendation V.24 interchange circuits. It applies when data transmission on a leased line is supported through a single physical interface that controls both the leased and back‑up facilities (e.g., GSTN, SDN or private switched lines). The standard defines how a Data Terminal Equipment (DTE) and Data Circuit‑terminating Equipment (DCE) exchange interface control and status signals to switch automatically or by authorization between primary leased lines and a single back‑up facility.
Key Topics
- Scope and intent: Protocol requirements for a single back‑up facility alternative to a leased line; guidance for other multi‑facility arrangements.
- DTE/DCE roles: Clear delineation of actions when switching is initiated by the DTE (direct mode) or by the DCE under DTE authorization (authorized mode).
- Interchange circuits: Use of ITU‑T V.24 signaling circuits (examples in the document include circuits 107, 108, 116, 117, 125) to indicate request, status and control during switching.
- Contact assignments: Mapping of interchange circuits onto connector pins - interchange circuit 116 = contact number 14; interchange circuit 117 = contact number 16 - applicable for the 25‑pole (ISO 2110) and 26‑pole (ISO/IEC 11569) connectors.
- Operational procedures: State diagrams and procedures for initiating, validating and terminating back‑up connections; handling automatic calling and validation to avoid erroneous switching.
- Modes of back‑up: Describes direct mode (DTE‑initiated switching) and authorized mode (DCE switches when authorized), and notes on automatic call establishment (reference to V.25bis).
Applications
ISO/IEC 8480:1995 is practical for:
- Telecom equipment manufacturers designing modems, terminal adaptors, and DCE units that must support leased‑line redundancy.
- Network engineers and system integrators implementing resilient leased‑line services with automatic failover.
- Service providers and enterprise IT teams planning backup connectivity strategies for critical data links.
The standard ensures consistent signaling behavior across equipment using ITU‑T V.24 interfaces, reducing mis‑switching risk and simplifying interoperability.
Related Standards
- ITU‑T V.24 - interchange circuits between DTE and DCE
- ITU‑T V.25bis - automatic calling procedures (referenced)
- ISO 2110 - 25‑pole DTE/DCE connector pin assignments
- ISO/IEC 11569 - 26‑pole interface connector dimensions and contact numbers
- ITU‑T V.110 / V.120 - terminal adaptor functions (referenced for ISDN/SDN back‑up)
Keywords: ISO/IEC 8480:1995, DTE/DCE interface, back‑up control, ITU‑T V.24, leased line backup, ISO 2110, ISO/IEC 11569.