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Technical Overview of ISO/IEC 13242-01: Private Integrated Services Network Inter-exchange Signalling Protocol – Call Diversion Supplementary Services
Guidance for Implementation and Compliance in PISN Environments Based on the Canadian Adoption CAN/CSA-ISO/IEC 13242-01
Introduction and Scope
The standard ISO/IEC 13242-01, formally adopted in Canada as CAN/CSA-ISO/IEC 13242-01, defines the inter-exchange signalling protocol for Call Diversion Supplementary Services in a Private Integrated Services Network (PISN). It is part of the ISO/IEC 12382 series (commonly referred to as QSIG) and governs how signalling information is exchanged between PISN nodes to activate, deactivate, and invocate call diversion (e.g., call forwarding unconditional, on busy, on no reply) across a corporate telecommunication network.
The standard applies to interfaces at the Q reference point between Private Integrated Services Network Exchanges (PINXs). It specifies the protocol for the control of supplementary services using the QSIG protocol stack as defined in ISO/IEC 11572 and ISO/IEC 11574. The primary audience includes network designers, PBX manufacturers, system integrators, and telecommunications engineers responsible for deploying multi-vendor PISN solutions.
Tip: The CAN/CSA version is identical in technical content to the international ISO/IEC standard and is referenced in many Canadian public sector telecommunication procurement requirements. Ensure you are using the latest amendment (typically the -01 edition reflects the main part; check for additional parts and corrigenda).
Technical Requirements and Protocol Specification
Signalling Protocol Structure
ISO/IEC 13242-01 specifies the use of the QSIG signalling layer (Layer 3) for call diversion supplementary services. The protocol information elements are carried within QSIG FACILITY and REGISTER messages as per the generic functional protocol defined in ISO/IEC 11582. The key elements include:
- Diversion Type: Forwarding unconditional, on busy, on no reply, or deflection.
- Diversion Number: The destination address to which the call is diverted.
- Originating User Information: The original calling party number.
- Activation/Deactivation/Interrogation: Procedures for remote management of diversion settings.
Message Types and Procedures
| Message Type | Operation Code (hex) | Use Case |
|---|---|---|
| DIVERSION REQUEST | 0x1C | Request to activate or deactivate a diversion service |
| DIVERSION RESPONSE | 0x1D | Acknowledge success or failure of the request |
| DIVERSION INVOKE | 0x1E | Remote PINX invokes diversion for a call (call forwarding scenario) |
| DIVERSION ERROR | 0x1F | Error indication (e.g., invalid destination, incompatible service) |
Call Diversion Scenarios
The standard defines three principal diversion scenarios:
- Call Forwarding Unconditional (CFU): All incoming calls are immediately diverted to the specified number.
- Call Forwarding on Busy (CFB): Diversion occurs only when the called party is busy.
- Call Forwarding on No Reply (CFNR): Diversion occurs when the called party does not answer within a network-defined time.
Each scenario requires precise interaction between the served PINX and the diverting PINX, as well as backward compatibility with basic call handling according to ISO/IEC 11571.
Warning: The protocol uses operation codes and information elements that must be supported identically by both ends of a QSIG link. Vendors must implement the full set of mandatory procedures as defined in clause 7 of the standard; otherwise, interworking issues will occur (e.g., call diverted to incorrect number or service not recognized).
Implementation Highlights for Network Operators
Implementing ISO/IEC 13242-01 in a multi-vendor PISN environment requires careful planning and testing. Key considerations include:
- Feature Interaction: Call diversion interacts with other supplementary services (e.g., call waiting, call transfer). The standard defines precedence rules; for example, diversion on busy takes priority over call waiting when the former is active.
- Inter-exchange Timing: Time-out values for the diversion procedures must be set according to Annex A of ISO/IEC 13242-01. Recommended defaults: T-DIV (3 s) for awaiting response, T-DIV-INV (6 s) for invoke procedure.
- Addressing: Diversion numbers are encoded using the numbering plan identified in ISO/IEC 11571. Private numbering plans must be consistent across all nodes.
- Call Detail Recording: While the standard does not mandate CDR, network operators should log diversion events for billing and troubleshooting.
Success: When correctly implemented, ISO/IEC 13242-01 enables seamless call diversion across a PISN composed of PINXs from different manufacturers, provided they pass the compliance tests defined in ISO/IEC 13242-1 (which is the conformance test specification for this standard).
Compliance and Testing Considerations
Conformance testing for ISO/IEC 13242-01 is based on the framework described in ISO/IEC 9646 (OSI conformance testing methodology) and the protocol-specific test suite deposited at regional test laboratories (e.g., ETSI in Europe, CSA in Canada).
Manufacturers seeking compliance certification for the Canadian market should follow the procedures outlined in CAN/CSA-ISO/IEC 13242-01. The certification process typically includes:
- Static conformance review – verification of the protocol implementation conformance statement (PICS).
- Dynamic behaviour tests – using automated test equipment to simulate normal and error conditions.
- Interoperability testing – pairing the implementation with at least two other certified implementations.
Common non-compliance issues observed in the field include incorrect handling of the “diverting cause” (reason for diversion) and failure to forward the original calling party number when required.
Danger: Using an implementation that does not comply with ISO/IEC 13242-01 can cause cascading call failures, especially in a large PISN with multiple call forwardings. Always verify that your PINX firmware version includes the mandatory procedures for the diversion service in question.
Frequently Asked Questions
Q: Is ISO/IEC 13242-01 applicable only to corporate PBXs?
A: The standard applies to any Private Integrated Services Network Exchange (PINX) that implements the QSIG signalling protocol. This includes traditional PBXs, IP-PBXs, and hybrid systems, as long as they support the Q reference point as defined in ISO/IEC 11571.
A: The standard applies to any Private Integrated Services Network Exchange (PINX) that implements the QSIG signalling protocol. This includes traditional PBXs, IP-PBXs, and hybrid systems, as long as they support the Q reference point as defined in ISO/IEC 11571.
Q: Can I use this standard with Voice over IP (VoIP) networks?
A: Yes. The QSIG protocol is transport-independent. When carried over IP networks (e.g., using RTP for media and Q.931/Q.921 encapsulation), the same service semantics apply. However, gateways or trunking gateways must map the diversion information elements correctly between the IP and TDM domains.
A: Yes. The QSIG protocol is transport-independent. When carried over IP networks (e.g., using RTP for media and Q.931/Q.921 encapsulation), the same service semantics apply. However, gateways or trunking gateways must map the diversion information elements correctly between the IP and TDM domains.
Q: What is the relationship between this standard and the European Telecommunications Standards Institute (ETSI) supplement for call diversion?
A: The ETSI TS 101 235 series is harmonized with the ISO/IEC 13242 series. In fact, many tests used in Europe are based on the same conformance analysis. The difference lies mainly in regional numbering plan details and specific regulatory requirements.
A: The ETSI TS 101 235 series is harmonized with the ISO/IEC 13242 series. In fact, many tests used in Europe are based on the same conformance analysis. The difference lies mainly in regional numbering plan details and specific regulatory requirements.
Last updated: 2026. This article is for informational purposes. Refer to the official CAN/CSA-ISO/IEC 13242-01 document for the complete normative text.