Overview - ISO/IEC 14841:1996 (Call Offer SS-CO)
ISO/IEC 14841:1996 defines the Call Offer supplementary service (SS-CO) for Private Integrated Services Networks (PISN). The standard specifies stage 1 (service description as seen by users) and stage 2 (functional model and information flows) for offering a call to a busy called user and waiting for that user to accept when resources free up. SS-CO applies to the basic services defined in ISO/IEC 11574 and fits into PISN/PINX architectures.
Key topics and technical requirements
- Service purpose: enable a calling user to request that a call be offered to a busy called user and to wait until the called user can accept the call (an “offered call”).
- Stage 1 vs Stage 2:
- Stage 1 (clause 6): user-visible behaviour, invocation methods, normal and exceptional procedures.
- Stage 2 (clause 7): functional entities (FE), functional model, information flows, FE actions and behaviour, and allocation to physical equipment.
- Invocation methods (a PISN must offer one or more):
- Network invocation (immediate) - network automatically invokes SS-CO when calling a busy user (per calling user profile).
- Consultation - caller may request SS-CO after being informed the destination is busy (within a consultation timer).
- Immediate invocation - caller requests SS-CO as part of initial call setup.
- Network invocation (delayed) - network automatically invokes SS-CO after informing caller the destination is busy unless caller clears within an automatic call offer invocation timer.
- Timers and timeouts: consultation timer and automatic call offer invocation timer govern user opportunities and automatic invocation; offered calls may time out.
- Interaction rules: SS-CO interacts with other supplementary services and additional network features (e.g., CLIP, COLP, CLIR, CNIP, CONP, CNIR, CCBS, CCNR, Call Transfer, Call Forwarding variants, Do Not Disturb, Call Intrusion, Path Replacement). Stage 2 defines inter-FE relationships and information flow sequences.
- Conformance: to claim conformance, a stage 3 specification (protocols and equipment behaviour) must adequately support the relevant aspects of stage 1 and 2.
Applications and who uses it
- Target users: telecom standards engineers, PBX/PINX vendors, enterprise telephony architects, telecom equipment manufacturers, and protocol developers.
- Practical uses:
- Corporate PBX/PISN feature sets - allowing callers to wait until busy employees free resources.
- Call center and enterprise telephony - queuing and offering calls to busy agents when resources are freed.
- Interoperability design - mapping SS-CO to signalling protocols in Stage 3 implementations.
- Benefits: improves call handling flexibility, reduces repeated call attempts, and integrates with identification and call completion features.
Related standards
- ISO/IEC 11574 (basic call services and functional capabilities)
- ISO/IEC 11579-1 (PINX reference configuration)
- Related PISN SS documents: name identification, call transfer, call completion, call diversion, DND/DNDO, identification supplementary services
- CCITT/ITU-T recommendations referenced for terminology and service description
Keywords: ISO/IEC 14841, Call Offer, SS-CO, PISN, Private Integrated Services Network, stage 1, stage 2, functional model, information flows, PBX, PINX, consultation timer.
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