ISO/IEC 15056:1997 PDF

Overview

ISO/IEC 15056:1997 defines the inter-exchange signalling protocol for the Transit Counter additional network feature (ANF-TC) at the Q reference point between Private Integrated Services Network Exchanges (PINXs) within a Private Integrated Services Network (PISN). ANF-TC limits how many transit PINXs a call setup may pass through to prevent indefinite routing loops. This International Standard is the stage‑3 signalling specification and operates together with basic circuit‑switched call control and connection‑oriented signalling protocols.

Key topics and technical requirements

• Scope & conformance
  • Stage‑3 protocol specification that satisfies stage‑1 and stage‑2 requirements in ISO/IEC 15055.
  • Conformance is demonstrated using the PICS (Protocol Implementation Conformance Statement) proforma (Annex A).
• Signalling behavior
  • ANF‑TC can be used with basic call SETUP or call‑independent (connection‑oriented) SETUP requests.
  • The feature is a network option; activation criteria and maximum allowed transits are network‑dependent.
• Transit counter information element
  • Encoded as a discrete information element in codeset 4 (ISO codeset).
  • Variable length, category‑1 format; carried in the SETUP message.
  • Transit count is a binary value in octet 3 (range 0–31). The network‑defined acceptable limit shall not exceed 31.
• Procedural roles
  • Originating PINX: may include Transit counter with value 0.
  • Transit PINX: increments and forwards the Transit counter when below the acceptable limit; may insert a Transit counter if missing.
  • Terminating PINX: ignores Transit counter on receipt.
  • Incoming/Outgoing Gateway PINXs: may initialize or use the Transit counter for interworking.
• Interactions
  • Specifies protocol interactions with many supplementary services and ANFs (examples: SS‑CNIP, SS‑CONP, SS‑CCBS, SS‑CT, SS‑CFU, ANF‑PR, ANF‑CINT, SS‑AOC).
  • Interaction handling follows the stage‑3 rules of the relevant supplementary‑service standards.

Applications and users

• Who uses this standard
  • Telecom equipment vendors implementing PINX inter‑exchange signalling.
  • Network architects and operators designing PISN routing and loop‑protection policies.
  • Protocol implementers, interoperability/test labs, and standards compliance teams.
• Practical benefits
  • Prevents signalling loops and indefinite routing in private telephony networks.
  • Enables consistent inter‑PINX behaviour for transit‑limitation across vendor equipment and gateways.
  • Supports safe interworking with other supplementary services and external networks.

Related standards

• ISO/IEC 15055 (ANF‑TC stage 1 & 2)
• ISO/IEC 11572 (circuit mode inter‑exchange signalling)
• ISO/IEC 11582 (generic protocol for supplementary services)
• ISO/IEC 11579‑1 (PISN reference configuration)
• Other referenced stage‑3 standards (ISO/IEC 13869, 13870, 13873, 13874, 15054)