Manual Commencement Mode

Description

Manual commencement mode is a call setup behavior defined for Mission Critical Push To Talk (MCPTT) services within 3GPP. In this mode, when an MCPTT user initiates a private call to another user, the call does not connect automatically. Instead, the receiving MCPTT user is alerted and must perform an explicit action—such as pressing a button or selecting an on-screen option—to accept or reject the incoming call. This contrasts with automatic commencement mode, where the call is established without callee intervention. The mode is specified in 3GPP TS 23.179 and TS 23.379, which define the functional architecture, procedures, and information flows for MCPTT.

The need for manual commencement arises from the operational requirements of mission-critical communications. In many public safety scenarios, users must have control over which calls they accept, especially when they are engaged in other activities or when the call may interrupt critical tasks. Manual commencement provides a mechanism for the callee to screen calls, ensuring that only authorized or desired communications are established. It also supports privacy and prioritization, as users can reject calls from unknown or lower-priority sources.

From an architectural perspective, manual commencement mode involves several MCPTT entities. The originating MCPTT client sends a call setup request to the MCPTT server. The server, upon determining that the target user is configured for manual commencement, forwards the call invitation to the terminating MCPTT client. The terminating client then alerts the user and waits for a response. If the user accepts, the client sends an acceptance message back to the server, which then completes the call setup and grants the floor to the originator. If the user rejects, the server notifies the originator of the rejection and the call attempt is terminated. This process is governed by the MCPTT service configuration, which may define timers for user response and fallback behaviors.

Manual commencement mode is particularly relevant in off-network and isolated E-UTRAN scenarios, where direct communication between UEs may be used. In such cases, the mode ensures that the callee is not forced into a call without consent. The mode can be configured per user or per group, and it may be overridden by emergency or imminent peril calls, which typically use automatic commencement to ensure immediate communication.

The feature has been part of MCPTT since its introduction in Release 13 and has remained stable across subsequent releases. Its definition has not undergone substantive changes, reflecting its fundamental role in mission-critical call control. As MCPTT evolves towards MCX (Mission Critical Services) encompassing video and data, manual commencement remains a key building block for user-centric call handling.

Purpose & Motivation

Manual commencement mode exists to give MCPTT users control over incoming private calls, ensuring that they can accept or reject call setups based on their current situation. This is critical in public safety and mission-critical environments where interruptions can have serious consequences. The mode addresses the need for callee consent, privacy, and prioritization, which are not adequately handled by automatic call setup mechanisms.

Before the introduction of MCPTT, mission-critical push-to-talk systems often used automatic call setup, which could lead to unwanted interruptions. Manual commencement provides a standardized way to implement call screening and user-controlled acceptance, aligning with the operational needs of first responders. It also supports regulatory and privacy requirements by allowing users to decline calls. The feature was introduced in Release 13 as part of the initial MCPTT specifications and has been maintained without significant changes, demonstrating its enduring relevance.