Overview
ISO/IEC 15507:1997 defines the signalling protocol (SYNC‑SIG) used to support clock synchronization between Private Integrated Services Network Exchanges (PINXs) that form a Private Integrated Services Network (PISN). The standard specifies how adjacent PINXs exchange Application Protocol Data Units (APDUs) over a call‑independent signalling connection to coordinate clock sources and maintain a common timing reference across the PISN. The synchronization method follows the approach described in annex F of ISO/IEC 11573.
Key topics and requirements
- Scope and applicability: Applies to PINXs interconnected to form a PISN and to the Synchronization Entity within each PINX responsible for timing.
- Signalling transport: SYNC‑SIG messages are carried in the FACILITY information element using the call‑independent (connection‑oriented) transport defined in ISO/IEC 11582.
- Operations and coding: The protocol defines ASN.1 operations (e.g., synchronizationRequest, synchronizationInfo) and associated argument/result structures. Information is encoded as Facility IE per ISO/IEC 11582.
- States and procedures: Logical states include SYNC‑Idle, SYNC‑Active, and SYNC‑Wait. Procedures specify actions for Requesting (originating) and Destination (terminating) PINXs during normal and exceptional conditions.
- Actions supported: Typical synchronization actions include enslavement, holdon, free‑running, and idle states as conveyed in the synchronization messages.
- Timers and protection: A protection timer T1 runs at the Requesting PINX in SYNC‑Wait to guard against missing responses; T1 is specified to be not less than 15 s.
- Conformance: Implementations must complete the Protocol Implementation Conformance Statement (PICS) proforma (Annex A) to declare supported capabilities.
Applications and who uses this standard
- Telecommunications equipment vendors and PBX/PINX manufacturers implement SYNC‑SIG to ensure interoperable clock synchronization across private networks.
- Network architects and operators deploy the protocol to prevent loss or misalignment of timed information between exchanges in a PISN.
- Test labs and conformance testers use the PICS proforma and message sequence examples (Annex B) and SDL procedural representations (Annex C) for validation.
- Developers integrating ISDN-like services in private networks use ISO/IEC 15507 to align synchronization behavior with ISO/IEC 11573 methods.
Related standards
- ISO/IEC 11573 - Synchronization methods and technical requirements for PISNs (methodology referenced by 15507)
- ISO/IEC 11582 - Generic functional protocol; transport and FACILITY message usage
- ISO/IEC 11579‑1 - Reference configuration for PISN Exchanges (PINX)
- ITU‑T recommendations (e.g., I.112, Z.100/SDL) referenced for terminology and SDL representations
ISO/IEC 15507 is essential when consistent timing across private exchanges matters - for reliable voice/data transfer, service integrity, and interoperable PISN deployments.