ISO/IEC 13872:2003

Overview

ISO/IEC 13872:2003 defines the Call Diversion supplementary services for Private Integrated Services Networks (PISN). It specifies four services: Call Forwarding Unconditional (SS‑CFU), Call Forwarding Busy (SS‑CFB), Call Forwarding No Reply (SS‑CFNR) and Call Deflection (SS‑CD). The standard contains stage 1 (user-facing service descriptions) and stage 2 (functional model and information flows) specifications, describing how diversions are invoked, the functional entities involved, and the signalling/information sequences needed to support these services in a PISN environment.

Key Topics and Requirements

• Services covered
  • SS‑CFU: unconditional forwarding of incoming calls.
  • SS‑CFB: forwarding when the destination is busy.
  • SS‑CFNR: forwarding when there is no reply.
  • SS‑CD: user‑initiated deflection or redirection of an incoming call.
• Stage 1 (user view): behavior, provisioning/withdrawal procedures, normal and exceptional call‑handling cases, and interactions with other supplementary services (e.g., CLIP, COLP, CLIR, call transfer, completion of calls).
• Stage 2 (functional model): identification and description of functional entities (FEs), allocation of functions to equipment, detailed information flows and example flow sequences. Stage 2 also provides functional entity actions and behaviour for diversion processing.
• Conformance: To claim conformance, a stage 3 standard (protocol level) must implement the aspects of stage 1 and stage 2 relevant to its interfaces/equipment.
• Interworking and deployment: includes interworking considerations for PISN exchanges and interactions with basic services defined in ISO/IEC 11574.

Practical Applications and Users

• Telecommunications equipment vendors designing PBX/PISN exchanges and features like call forwarding and deflection.
• Protocol engineers and system integrators developing stage‑3 signalling protocols that must interoperate with PISN call diversion services.
• Network architects and service providers implementing enterprise telephony solutions who require standardized behavior for call diversion across nodes.
• Test labs and conformance bodies validating that equipment follows the stage 1/2 functional and information‑flow requirements.

Benefits

• Ensures consistent user experience for call forwarding and deflection features across vendors.
• Provides a clear functional model for implementing diversion logic and tracing information flows.
• Facilitates interoperability between PISN components and simplifies stage‑3 signalling design.

Related Standards

• ISO/IEC 11574 (basic call services and capabilities)
• ISO/IEC 11571 (addressing)
• ISO/IEC 11579‑1 (PISN exchange reference configuration)
• ETS 300 387 (method for specification of services)
• ITU‑T recommendations referenced for terminology and SDL (e.g., I.112, I.210, Z.100)

Keywords: ISO/IEC 13872:2003, Call Forwarding, Call Deflection, SS‑CFU, SS‑CFB, SS‑CFNR, SS‑CD, PISN, stage 1, stage 2, functional model, information flows.