To Be Determined

Description

In the context of 3GPP standardization, 'To Be Determined' (TBD) is a formal placeholder notation used within technical specifications (TS) and technical reports (TR). It signifies that a specific technical aspect—such as a parameter value, an algorithm detail, a message field, or even an entire functional procedure—has not been agreed upon or fully specified at the time of publication of that particular document version. The use of TBD is a critical project management tool within the standards development process, allowing working groups to advance the overall architecture and framework of a feature without being blocked by unresolved technical debates or dependencies on other work items.

The notation is systematically applied across various specification series. For instance, in protocol specifications (e.g., the 24-series, 25-series, 36-series, 38-series), a TBD might appear in an information element table, indicating a code point or a length is pending. In service requirements (22-series) or architecture descriptions (23-series), it might denote that a specific service capability or network function behavior is under study. The resolution of a TBD is a key deliverable for subsequent releases or specification updates, often documented in change requests (CRs) that replace the TBD text with the finalized technical content.

The lifecycle of a TBD entry is governed by the 3GPP specification numbering and versioning rules. A specification containing TBDs is published with the understanding that these open items will be closed, typically before the specification reaches a stable, implementable state (e.g., at the end of a Release). The resolution process involves technical discussions, simulations, and consensus-building within the relevant Technical Specification Group (TSG) or Working Group (WG). Once resolved, the specification is updated, and the TBD marker is removed, providing clarity to equipment manufacturers and network operators for implementation.

Purpose & Motivation

The primary purpose of the TBD placeholder is to facilitate the parallel and incremental development of complex telecommunications standards. 3GPP standards encompass thousands of pages across hundreds of specifications, developed by hundreds of companies. It is impractical to finalize every minute detail simultaneously. The TBD mechanism allows different parts of the system to be specified independently and at different paces. For example, the radio access network (RAN) working groups can define a new physical layer channel structure while marking certain higher-layer control parameters as TBD, which can later be filled in by the core network (CT) or service and system aspects (SA) groups based on overall system requirements.

Historically, without such a mechanism, standardization would risk significant delays or the publication of inconsistent specifications. TBD provides a structured way to manage uncertainty and dependencies. It explicitly signals to readers of the specification—engineers, researchers, and implementers—which parts are stable and which are subject to change, preventing premature implementation based on assumptions. This is especially important for forward-looking features studied in early releases (e.g., in a Study Item phase), where the feasibility is explored before normative work begins, and many aspects are intentionally left as TBD until the feasibility is confirmed.