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CAN/CSA-ISO/IEC 13869-04: Private Integrated Services Network – Call Waiting Supplementary Service Protocol
Technical Overview of the Inter-exchange Signalling Protocol for Call Waiting in Private Telecommunication Networks
The standard CAN/CSA-ISO/IEC 13869-04 is the official Canadian adoption of the international joint standard ISO/IEC 13869:2004. It defines the inter-exchange signalling protocol for the Call Waiting supplementary service within a Private Integrated Services Network (PISN). As part of the QSIG family of protocols, this standard ensures consistent call-waiting behavior across multi-vendor private telecommunication environments. This article provides a detailed technical breakdown of its scope, core requirements, practical implementation guidelines, and compliance considerations.
Scope of CAN/CSA-ISO/IEC 13869-04
CAN/CSA-ISO/IEC 13869-04 specifies the generic functional protocol for the Call Waiting supplementary service at the Q reference point between Private Integrated Services eXchanges (PINX) within a PISN. The standard covers:
- Protocol procedures for activating, deactivating, and invocation of call waiting.
- Signalling message definitions, including call waiting indications and notifications.
- State transitions for the served user, calling user, and call-waiting user.
- Interworking with other supplementary services (e.g., call transfer, call hold).
- Compatibility requirements for transparent transport across tandem PINXs.
The standard applies to both basic call waiting (one waiting call) and multiple-waiting-call scenarios. It does not cover user interface or terminal equipment aspects, focusing exclusively on the network layer signalling protocol.
Technical Requirements
Protocol Architecture
The protocol is based on the OSI model, specifically the Network Layer (Layer 3) of the DSS1 signalling protocol. It uses the QSIG-CW protocol entity, which operates over the existing call control procedures defined in ISO/IEC 11572. The standard requires:
- Use of the CALL PROCEEDING and ALERTING messages to convey call-waiting information.
- An explicit Call Waiting Indicator (CWI) information element embedded in signalling messages.
- Support for three operational states: Idle, Waiting Call, and Call Waiting Answered.
Message Elements
The standard defines a set of mandatory and optional information elements for call-waiting signalling. The key elements are summarised in the table below.
| Information Element | Codepoint (hex) | Mandatory (M) / Optional (O) | Description |
|---|---|---|---|
| Call Waiting Indicator | 0x18 | M | Indicates a call is waiting for the served user. Contains subfields for queue length and priority. |
| Notification Indicator | 0x27 | M | Confirms that the waiting call has been presented (or rejected) by the served user. |
| Calling Party Number | 0x6C | O | Transfers the calling line identity to the user being notified of a waiting call. |
| Called Party Number | 0x70 | O | Identifies the served user’s extension for multiple-address scenarios. |
| Progress Indicator | 0x1E | O | Signals interworking situations, e.g., when connecting to a non-PISN network. |
State Machine
The call-waiting process follows a deterministic state machine with transitions driven by user actions and timer expiries. The standard specifies three main states with up to 26 allowed transitions. Timers T301–T305 guard waiting and answer intervals; typical defaults are 30–120 seconds.
Implementation Highlights
When deploying CAN/CSA-ISO/IEC 13869-04 in a real-world PISN, developers and network engineers should consider the following:
Tip: Use the standard’s component-based approach to integrate call waiting with Call Transfer (ISO/IEC 13868) or Call Hold (ISO/IEC 13870). Most QSIG implementations bundle these services; ensure inter-locking of call states to avoid conflict when the served user tries to transfer a waiting call before answering it.
Warning: The protocol expects that each waiting call is tracked via a unique call reference at the network layer. If a PINX fails to properly correlate these references, waiting calls may be presented to the wrong user or lost entirely. Always implement robust call reference pairing in the service logic.
Other important implementation points include:
- Backward compatibility: The standard is fully upward compatible with the base call control of ISO/IEC 11572. No changes are required to existing call handling if call waiting is not activated with the served user.
- Priority queuing: The Call Waiting Indicator subfield “queue position” allows up to 15 waiting calls. Systems should honour FIFO unless a higher-priority call is explicitly signalled.
- Overload management: In high-usage scenarios, a PINX may refuse incoming waiting calls by sending a CALL WAITING REJECT notification. The standard permits this as an exception, but the network must remain stable.
Compliance and Certification Notes
Conformance to CAN/CSA-ISO/IEC 13869-04 is typically verified through a combination of static and dynamic testing. Organisations seeking certification should be aware of the following:
Success factor: Products that successfully pass the conformance test suite defined in the standard’s companion PICS (Protocol Implementation Conformance Statement) listing achieve full interoperability with any other conformant system, eliminating vendor lock-in and reducing integration costs.
Non-compliance risk: A PINX that does not correctly encode the Call Waiting Indicator (e.g., using a wrong length or missing a mandatory subfield) will cause the waiting call to be rejected by the remote end. This can lead to dropped calls and user dissatisfaction. Ensure comprehensive protocol conformance testing before deployment.
Key compliance aspects include:
- PICS documentation: The standard requires manufacturers to submit a PICS that states which optional features are implemented (e.g., multiple waiting calls, priority indication). Reviewers use this to validate conformance.
- Interworking testing: Because private networks often connect to public ISDN/IP networks, the standard defines interworking profiles (Annex C) for SIP and ISDN interworking. Compliance requires successful testing of the specified mapping functions.
- Version control: CAN/CSA-ISO/IEC 13869-04 is based on the 2004 edition of ISO/IEC 13869. Any later amendments (e.g., corr. 1:2006) are not adopted unless explicitly cited. Always verify the adoption date (2004) in your purchase documentation.
Frequently Asked Questions
Q: Does CAN/CSA-ISO/IEC 13869-04 cover call waiting in VoIP environments?
A: The standard was written for circuit-switched PISN (QSIG). However, its service definition and state machine have been used as a basis for call waiting in some VoIP gateways that emulate QSIG signalling. Pure SIP-based call waiting is defined by IETF RFC 5359, but interworking with QSIG may require transcoding as per the profiles in Annex C of the standard.
A: The standard was written for circuit-switched PISN (QSIG). However, its service definition and state machine have been used as a basis for call waiting in some VoIP gateways that emulate QSIG signalling. Pure SIP-based call waiting is defined by IETF RFC 5359, but interworking with QSIG may require transcoding as per the profiles in Annex C of the standard.
Q: What is the Q reference point mentioned in the scope?
A: The Q reference point is the logical interface between two Private Integrated Services Exchanges (PINXs) within a PISN. It is described in ISO/IEC 11579-1. CAN/CSA-ISO/IEC 13869-04 specifies the signalling exchanged at this point to support call waiting across the network.
A: The Q reference point is the logical interface between two Private Integrated Services Exchanges (PINXs) within a PISN. It is described in ISO/IEC 11579-1. CAN/CSA-ISO/IEC 13869-04 specifies the signalling exchanged at this point to support call waiting across the network.
Q: How does call waiting interact with the Call Completion to Busy Subscriber (CCBS) service?
A: If both services are active, a busied user receiving a new incoming call can either let it wait (call waiting) or reject it to trigger CCBS. The standard defines a precedence in Annex B: call waiting is attempted first; if the user does not answer within a timert, the call is either released or sent to voice mail, and CCBS may then be offered. Inter-service arbitration must comply with the priority rules in the PICS.
A: If both services are active, a busied user receiving a new incoming call can either let it wait (call waiting) or reject it to trigger CCBS. The standard defines a precedence in Annex B: call waiting is attempted first; if the user does not answer within a timert, the call is either released or sent to voice mail, and CCBS may then be offered. Inter-service arbitration must comply with the priority rules in the PICS.
The year 2026 is used for copyright and reference purposes in this article. Always refer to the latest CSA or ISO/IEC catalogue for the current version of the standard.