Call Completion Signalling in Private Networks: An Overview of CAN/CSA-ISO/IEC 13868-04

Scope and Application

CAN/CSA-ISO/IEC 13868-04 (the Canadian adoption of ISO/IEC 13868:2004) defines the inter-exchange signalling protocol for call completion supplementary services within a Private Integrated Services Network (PISN). The standard specifies how Call Completion to Busy Subscriber (CCBS) and Call Completion on No Reply (CCNR) are executed between Private Integrated services Network eXchanges (PINX) using the QSIG signalling protocol.

The scope of this standard covers the stage 3 specification—i.e., the signalling procedures, messages, information elements, and state transitions necessary to realize the call completion features across network boundaries. It is applicable to any PINX that supports the QSIG call completion supplementary services and ensures interoperability between different vendors’ equipment.

CAN/CSA-ISO/IEC 13868-04 addresses three principal aspects:

• Service description — The logical behaviour of CCBS and CCNR from the user’s perspective;
• Signalling protocol — The precise messages, information elements, and state machines exchanged between PINX nodes;
• Conformance requirements — The mandatory and optional capabilities a system must declare to claim compliance.

This standard is part of the broader family of PISN signalling standards (ISO/IEC 11574 series) and is closely related to ISO/IEC 11582 (generic functional protocol for the support of supplementary services). It is intended for telecom engineers, network architects, and compliance testers.

Technical Requirements

QSIG Signalling for Call Completion

The inter-exchange signalling defined by CAN/CSA-ISO/IEC 13868-04 is based on the QSIG protocol stack. Call completion involves the following high-level steps:

1. Service Request — The calling user (A) requests CCBS or CCNR when the called user (B) is busy or does not answer.
2. Monitoring — The network monitors the state of user B until the appropriate condition (idle for CCBS, no reply timeout for CCNR) is satisfied.
3. Recall — When the condition is met, the network initiates a new call attempt from A to B automatically (or with a limited ring).
4. Completion — The call is established normally, or the service is cancelled after a defined number of recall attempts.

The standard specifies a set of QSIG messages extended with specific call completion and call independent information elements. Key messages include:

Comparison of CCBS and CCNR

The following table summarises the distinct conditions and network behaviour for each service:

Implementation Highlights

Implementing CAN/CSA-ISO/IEC 13868-04 requires careful handling of several complex aspects within a PINX:

• Resource Reservation — To guarantee that a recall can be completed, the originating PINX may optionally reserve network resources (e.g., a trunk) while monitoring the called user. This is signalled using the Call Resource Information element.
• Timer Management — The standard defines mandatory timers (e.g., T_CC_Monitor, T_CC_Recall) to prevent indefinite monitoring. Their values must be configurable per service provider policy.
• Interworking with Other Services — CCBS/CCNR must interact gracefully with call forwarding (diverting), call transfer, and call waiting. For instance, when call forwarding is active, the network may either disable call completion or forward the request to the forward‑to user. CAN/CSA-ISO/IEC 13868-04 provides a precedence order.
• QSIG Protocol Stack — The standard relies on the underlying QSIG layer (ISO/IEC 11572) and the generic functional procedures of ISO/IEC 11582. The application protocol data units are encapsulated in FACILITY messages.

Example Message Sequence

A simplified QSIG message flow for CCBS (using call‑independent signalling) is shown below (user A initiates a call, finds user B busy, activates CCBS, then later the recall succeeds):

1. SETUP (A→B) – Initial call attempt.
2. RELEASE COMPLETE (B→A) – User B busy; includes cause “busy”.
3. FACILITY (A→B) – CCBS activation request (Facility IE with CC‑Setup).
4. FACILITY (B→A) – CCBS activation acknowledgment (CC‑Setup Ack).
5. Monitoring period – User B clears previous call.
6. FACILITY (B→A) – Indication that B is idle (CC‑Recall).
7. SETUP (A→B) – New call attempt triggered automatically.
8. CONNECT (B→A) – B answers; call completed.

Compliance and Testing

Conformance to CAN/CSA-ISO/IEC 13868-04 is typically verified using the following methods:

• Static Conformance Review — Compare the supplier’s PICS with the standard’s mandatory and conditional requirements. All static capabilities (e.g., supported scenarios, message support) must be declared.
• Dynamic Conformance Testing — Execute a set of test cases covering normal call completion, service cancellation, recall timeout, error handling, and interaction with other supplementary services.
• Network Simulation — Use a QSIG protocol tester that can emulate both originating and terminating PINX behaviour.

The Canadian Standards Association (CSA) requires that any product claiming compliance to CAN/CSA-ISO/IEC 13868-04 must undergo testing by an accredited laboratory. In most cases, a certificate of compliance to ISO/IEC 13868 issued by a recognized body (e.g., ETSI, SIP-SCF) is accepted as equivalent.

For ongoing compliance, network operators should regularly verify that all PINX nodes in a PISN run the same version of the protocol to avoid race conditions during monitoring. The standard does not mandate backward compatibility with earlier proprietary call completion schemes; a phased migration plan is recommended.

Article prepared for technical documentation purposes. Standard reference: CAN/CSA‑ISO/IEC 13868‑04 (equivalent to ISO/IEC 13868:2004). All rights reserved. Year: 2026.